U.S. patent application number 15/021828 was filed with the patent office on 2016-08-11 for a rock removal body.
This patent application is currently assigned to ELEMENT SIX ABRASIVES S.A.. The applicant listed for this patent is ELEMENT SIX ABRASIVES S.A.. Invention is credited to MOOSA ADIA, GEOFFREY DAVIES, RUFUS NEETHLING.
Application Number | 20160230473 15/021828 |
Document ID | / |
Family ID | 49552728 |
Filed Date | 2016-08-11 |
United States Patent
Application |
20160230473 |
Kind Code |
A1 |
DAVIES; GEOFFREY ; et
al. |
August 11, 2016 |
A ROCK REMOVAL BODY
Abstract
A rock removal body comprises a PCD material (601) bonded to a
substrate (602) along an interface. The body is of right circular
cylindrical shape and the PCD material has a thickness (607) from
the circumferential edge axially along the surface of the barrel
portion of around 3 mm or greater, and a functional working volume
(606) having a maximum extent such that the final wear surface does
not intersect the interface of the PCD material volume and the
substrate. The PCD material volume comprises a diamond network and
a metallic component forming a metallic network, the substrate
comprises a cementing metal, the metallic component and the
cementing metal being independent of one another, independently
derived, have not interacted during the high pressure high
temperature manufacturing process, are measurably distinguishable
and are preselected to be different with respect to their alloy
composition. The PCD material encompasses the functional working
609 volume and is homogeneous.
Inventors: |
DAVIES; GEOFFREY; (SPRINGS,
ZA) ; ADIA; MOOSA; (SPRINGS, ZA) ; NEETHLING;
RUFUS; (SPRINGS, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELEMENT SIX ABRASIVES S.A. |
Luxembourg |
|
LU |
|
|
Assignee: |
ELEMENT SIX ABRASIVES S.A.
LUXEMBOURG
LU
|
Family ID: |
49552728 |
Appl. No.: |
15/021828 |
Filed: |
September 15, 2014 |
PCT Filed: |
September 15, 2014 |
PCT NO: |
PCT/EP2014/069587 |
371 Date: |
March 14, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 29/08 20130101;
C22C 26/00 20130101; E21B 10/5735 20130101; E21B 10/50 20130101;
B22F 7/064 20130101; E21B 10/58 20130101; E21B 10/54 20130101; E21B
10/567 20130101; B22F 2005/001 20130101 |
International
Class: |
E21B 10/58 20060101
E21B010/58; E21B 10/54 20060101 E21B010/54; E21B 10/50 20060101
E21B010/50; E21B 10/567 20060101 E21B010/567 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2013 |
GB |
1316456.1 |
Claims
1. A rock removal body for a drag bit rock drilling application
comprising a polycrystalline diamond (PCD) material volume bonded
to a cemented hard metal substrate along an interface; wherein: a.
the body has an overall body volume, and is of a right circular
cylindrical shape having a circumferential edge, and a barrel
portion, the PCD material volume being axially asymmetrically
disposed at one end of the body; b. the PCD material volume has a
thickness from the circumferential edge axially along the surface
of the barrel portion of around 3 mm or greater and a functional
working volume, the functional working volume being the volume of
PCD material progressively worn away in use during useful life of
the rock removal body to a form a final wear surface, the
functional working volume having a maximum extent such that the
final wear surface does not intersect the interface of the PCD
material volume and the substrate; c. the interface bonding the
polycrystalline diamond material volume to the cemented hard metal
substrate comprising a layer of a third material derived from a
refractory material, the third material being a metal diffusion
blocking barrier material to molten bonding material of the
substrate and molten catalyst solvent sintering aid of the PCD
material volume during formation of the rock removal body; d. the
PCD material volume comprising a plurality of inter-bonded diamond
grains having an average diamond grain size forming a diamond
network and a metallic component forming a metallic network, and
the substrate comprising a cementing metal, the metallic component
and the cementing metal being independent of one another,
independently derived, have not interacted during the high pressure
high temperature manufacturing process, are measurably
distinguishable and are pre-selected to be different with respect
to their alloy composition; e. the PCD material at least
encompasses the functional working volume and is homogeneous in
that the PCD material is spatially constant and invariant with
respect to diamond network to metallic network volume ratio,
wherein the homogeneity is measured at a scale greater than ten
times the average diamond grain size, the maximum diamond grain
size in the diamond network being less than three times the average
diamond grain size.
2. The rock removal body of claim 1, wherein the PCD material
volume has a thickness and the substrate has a length along the
barrel portion, wherein the ratio of the PCD thickness to the
substrate length measured along the barrel portion of the cylinder,
is always less than 1.0 and the volume of PCD material in the rock
removing body is less than about 50 percent of the overall body
volume.
3. The rock removal body of claim 2, wherein the body has a base
formed by a free face of the substrate, and wherein the PCD
material volume is a cylindrical layer having a thickness of about
3 mm or greater, the thin layer of third material forming the
interface between the PCD material volume and the substrate having
a thickness, wherein the combined thickness of the thin layer
forming the interface and the length of the substrate is about 8 mm
or greater, the thin layer forming the interface being
substantially flat, substantially planar and substantially parallel
to the base of the body.
4. The rock removal body of claim 3, wherein the body has a
diameter in the range of about 12 mm to about 20 mm, and the body
has an overall length measured along the barrel portion in the
range of about 11 mm to about 20 mm.
5. The rock removal body of claim 1, wherein the PCD material which
at least encompasses the functional working volume has an average
grain size of less than about 10 microns and a metal content in the
range of about 5 to about 9 volume percent.
6. A rock removal body for a roller cone bit rock drilling
application comprising a polycrystalline diamond (PCD) material
volume bonded to a cemented hard metal substrate along an
interface; wherein: a. the body comprises a right circular cylinder
portion having an associated radius, one end of the cylinder
portion forming a generally convex curved surface or surfaces with
an apex, or one end forming a general chisel shape where two or
more flat surfaces meet to form an apex, the PCD material volume
being axially asymmetrically disposed extending from and abutting
the apex, the cemented hard metal substrate being disposed at the
opposite end of the cylinder; b. the PCD material volume has a
thickness from the apex in the axial direction of the cylinder
portion of the body to the interface with the substrate equal to or
greater than the radius of the cylinder portion of the body, the
PCD material volume further comprising a functional working volume,
the functional working volume being the volume of PCD material
progressively worn away in use during useful life of the rock
removal body to a form a final wear surface, the functional working
volume having a maximum extent such that the maximum extent of the
functional working volume is less than the thickness of the PCD
material volume thickness; the functional working volume extending
from the apex in the axial direction; c. the interface bonding the
PCD material volume to the substrate comprising a thin layer of a
third material derived from a refractory material, the third
material being a metal diffusion blocking barrier material to
molten bonding material of the substrate and molten catalyst
solvent sintering aid of the PCD material volume during formation
of the rock removal body; d. the PCD material volume comprising a
plurality of inter-bonded diamond grains having an average diamond
grain size forming a diamond network and a metallic component
forming a metallic network, and the substrate comprising a
cementing metal, the metallic component and the cementing metal
being independent of one another, independently derived, have not
interacted during the high pressure high temperature manufacturing
process, are measurably distinguishable and are pre-selected to be
different with respect to their alloy composition; e. the PCD
material at least encompasses the functional working volume and is
homogeneous in that the PCD material is spatially constant and
invariant with respect to diamond network to metallic network
volume ratio, wherein the homogeneity is measured at a scale
greater than ten times the average diamond grain size, the maximum
diamond grain size in the diamond network being less than three
times the average diamond grain size.
7. The rock removal body of claim 6, wherein the generally convex
curved surface or surfaces comprising the apex is any one of
hemi-spheroidal, prolate hemi-spheroidal, oblate hemi-spheroidal,
or hemispherical; wherein the body comprises a shoulder formed by
the line of departure of the barrel portion extending into the
generally convex curved surface; and wherein the thin layer of the
third material forming the interface between the PCD material
volume and the substrate intersects the barrel portion below the
shoulder.
8. The rock removal body of claim 7, wherein the generally convex
curved surface is hemispherical, the radius of the cylinder portion
of the body being around 8 mm.
9. The rock removal body of claim 6, wherein the generally convex
curved surface is a cone having a rounded apex, wherein the rounded
apex has an associated radius, the radius of the rounded apex being
between around a quarter to around a half of the radius of the
cylinder portion of the body, wherein the body comprises a shoulder
formed by the line of departure of the barrel portion extending
into the generally convex curved surface; and wherein the thin
layer of the third material forming the interface between the PCD
material volume and the substrate intersects the barrel portion
below the shoulder.
10. The rock removal body of claim 9, wherein one end of the body
forms a chisel shape comprising a conical surface with a rounded
apex modified by two symmetrical inclined flat surfaces which meet
at the rounded apex, wherein the body comprises a shoulder formed
by the line of departure of the barrel portion extending into the
generally convex curved surface; and wherein the thin layer of the
third material forming the interface between the PCD material
volume and the substrate intersects the barrel portion below the
shoulder.
11. The rock removal body of claim 6, wherein the volume of the PCD
material volume is greater than the volume of the substrate.
12. The rock removal body of claim 11 wherein the substrate has an
associated radius and a thickness measured as the length of the
barrel portion which the substrate forms, the length of the
substrate being greater than the radius of the substrate.
13. (canceled)
14. (canceled)
15. The rock removal body of claim 1, wherein the thin layer of the
third material forming the interface between the PCD material
volume and the substrate comprises a partially carburised
refractory metal layer having a thickness of between around 20
microns and around 100 microns, the partially carburised refractory
metal layer comprising any one or more of tantalum, vanadium,
molybdenum, zirconium, tungsten and alloys thereof.
16. The rock removal body of claim 15, wherein the thin layer of
the third material forming the interface between the PCD material
volume and the substrate comprises a partially carburised layer of
tantalum.
17. The rock removal body of claim 1, wherein the thin layer of the
third material forming the interface between the PCD material
volume and the substrate comprises a PVD or a CVD deposited
continuous ceramic layer having a thickness of greater than around
3 microns, the thin layer of the third material comprising any one
or more of nitrides of the elements of groups IVa, Va and/or VIa of
the periodic table.
18. The rock removal body of claim 17, wherein the thin layer of
the third material comprises titanium nitride.
19. (canceled)
20. (canceled)
21. The rock removal body of claim 1, wherein the metal forming the
metallic network of the PCD material volume is invariant as regards
the metal type or alloy across the dimensions of the PCD material
volume; and wherein the metallic content of the PCD material
increases in the general direction away from a point which is part
of the functional working volume which initially bears upon the
rock in use, towards the thin layer of the third material forming
the interface between the PCD material volume and the
substrate.
22. The rock removal body of claim 21, wherein the PCD material
volume comprises two or more layers of differing PCD material, the
first layer of lowest linear coefficient of thermal expansion and
metal content extends from the free surface of the PCD material
volume and encompasses the functional working volume, the second or
subsequent layers of higher linear coefficient of thermal expansion
and metal content separating the first layer from the thin layer
forming the interface between the PCD material volume and the
substrate.
23. The rock removal body of claim 1, wherein the body has a base
portion formed by the free surface of the substrate; wherein the
substrate has an associated linear coefficient of thermal expansion
which decreases away from the central point of the base of the body
towards the thin layer forming the interface between the PCD
material volume and the substrate.
24. The rock removal body of claim 23, wherein the substrate
comprises a cementing metal material and a hard compound, the
cementing metal material and the hard compound being invariant as
regards metal type and molecular composition, the amount of
cementing metal decreasing in a direction away from the central
point of the base of the body towards the thin layer of the third
material forming the interface between the PCD material volume and
the substrate.
25. The rock removal body of claim 24, wherein the substrate
comprises two or more layers of differing hard metal material, the
first layer of highest linear coefficient of thermal expansion and
metal content extending from the free surface of the substrate
forming the base of the body, the second and/or subsequent layers
being of lower linear coefficient of thermal expansion and metal
content separating the first layer from the thin layer forming the
interface between the PCD material volume and the substrate.
26. The rock removal body of claim 1, wherein the PCD material
volume is graded in composition and structure such that the linear
coefficient of thermal expansion of the PCD material increases in a
direction away from a point which is part of the functional working
volume towards the interface, the linear coefficient of thermal
expansion of the substrate decreasing in a direction away from the
central point of the base of the body towards the interface.
27. (canceled)
28. (canceled)
29. (canceled)
30. (canceled)
Description
FIELD
[0001] This disclosure relates to a rock removal body for a drag
bit rock drilling application and a rock removal body for a roller
cone bit rock drilling application
[0002] Background
[0003] Polycrystalline diamond materials (PCD) typically comprise
an intergrown network of diamond grains with an interpenetrating
metallic network. The network of diamond grains is formed by
sintering of diamond powders facilitated by molten metal
catalyst/solvent for carbon at elevated pressures and temperatures.
The diamond powders may have a monomodal size distribution whereby
there is a single maximum in the particle number or mass size
distribution, which leads to a monomodal grain size distribution in
the diamond network. Alternatively, the diamond powders may have a
multimodal size distribution where there are two or more maxima in
the particle number or mass size distribution, which leads to a
multimodal grain size distribution in the diamond network. Typical
pressures used in this process are in the range of around 4 to 7
GPa but higher pressures up to 10 GPa or more are also practically
accessible and may be used. The temperatures employed are above the
melting point at such pressures of the metals. The metallic network
is the result of the molten metal freezing on return to normal room
conditions and will inevitably be a high carbon content alloy. In
principle, any molten metal solvent for carbon which can enable
diamond crystallization at such conditions may be employed. The
transition metals of the periodic table and their alloys may be
included in such metals.
[0004] Conventionally, the predominant custom and practice is to
use the binder metal of hard metal substrates caused to infiltrate
into a mass of diamond powder, after melting of such binders at the
elevated temperature and pressure. This is infiltration of molten
metal at the macroscopic scale of the conventional PCD
construction, i.e., infiltrating at the scale of millimetres. By
far the commonest conventional situation is the use of tungsten
carbide, with cobalt metal binders, as the sintered hard metal
substrate. This inevitably results in the sintered hard metal
substrate being bonded in-situ to the resultant PCD. Successful
commercial exploitation of PCD materials to date has been very
heavily dominated by such custom and practice.
[0005] For the purposes of this disclosure, PCD constructs which
use sintered hard metal substrates as a source of the molten metal
sintering agent via directional infiltration and the bonding
in-situ to that substrate, are referred to as "conventional PCD"
constructions or bodies.
[0006] Historically, conventional PCD structures comprising PCD
material bonded and attached to carbide hard metal substrates are
used for material removal elements attached and arranged in housing
bodies. General applications where the material to be removed is
rock include drill bits for oil well and mining purposes and the
like. PCD structures may also find application in, for example, as
road planing and building construction where the material to be
removed may be considered as synthetic or re-constituted rock-like
materials such as asphalt, rock chipping containing asphalt,
concrete, brick and the like, including combinations of such.
Henceforth, as used herein the term "rock" will be considered to
refer to both natural geological rocks and synthetic or
re-constituted rock-like materials.
[0007] Very important applications such as oil well drilling use
two main streams of drilling technology, either in competition with
or complementing each other. These are drag bit and roller cone
technologies. Both of these technologies exploit conventional PCD
structures..sup.1
[0008] FIG. 1 is a schematic diagram of a typical conventional drag
bit, 101, and housing body, 102. The diagram shows conventional PCD
rock removal elements 103, 104, and 105 in different radial
positions in the housing body, consisting of right circular
cylinders comprising relatively thin layers of PCD material bonded
and attached to much larger carbide hard metal cylindrical
substrates. On rotation of the drill bit, such elements are caused
to continuously bear on the rock and operate by a predominantly
shearing action, where the rock is progressively fractured and
fragmented. FIG. 2 schematically shows one edge of a conventional
PCD rock cutting element, 201, continuously shearing rock, 202.
[0009] Such drag drill bit designs have been extensively optimized
over many years such that the dominant and convenient custom and
practice is to exploit right cylindrical rock removal elements
which are brazed into cylindrical recessed pockets such that, on
rotation of the drill bit, overlapping of the sweep of the cutters
or rock removal elements provides for rock removal across the full
face of the drill bit. These highly established and optimized drill
bit designs with the attendant brazing technologies for attachment
of the cylindrical cutting elements are not lightly or conveniently
altered. Thus, desired and improved rock removal elements or
cutters are still conveniently restricted to overall right
cylindrical shapes and geometries. Moreover, the establishment of
the barrel of rock removal elements or cutters being made of hard
and wear resistant hard metals, providing appropriate mechanical
wear and brazability properties is a generally desired and not a
lightly changed aspect of the present drilling paradigm.
[0010] FIG. 3 is a schematic diagram of a typical roller cone drill
bit, 301, consisting of a housing body, 302, and three roller cone
structures, 303, which are able to freely rotate on bearings. Each
roller cone, 303, rotates around the surface of the rock as the
overall drill bit housing body, 302, is rotated. The rock removal
elements or bodies, 304, are inserted and attached to the surface
of each of the three cone structures. As the cone structures turn,
they bring the rock removing elements sequentially to bear on the
rock surface. The roller cone structures are attached to the
housing body via shaft and bearing structures which are in turn
protected by gage pad surfaces, 305, with abrasion resistant gage
elements, 306. Water cooling and crushed rock removal is
facilitated by nozzles, 307. In this case the rock removing
elements, 304, have typically rounded ends such as general chisel
shapes, or domed and/or conical surfaces which bear upon the rock
surface. These rock removal elements typically have a relatively
thin PCD material layer bonded with the shaped hard metal
substrate, and remove rock by a predominantly crushing action. This
is illustrated in FIG. 4 which schematically shows a cross-section
of a dome shaped conventional PCD rock crushing element, 401,
consisting of a thin layer of PCD material, 402, forming a shell
bonded to a dome shaped hard metal body, 403, bearing and crushing
rock, 404.
[0011] Similarly to drag bit designs, roller cone designs are
highly optimized and established. These too, therefore, are not
lightly and conveniently altered. Thus, it would be advantageous
for improved rock removal or rock crushing elements intended for
roller cone bits to have shapes and geometries with a right
cylindrical barrel made from easily brazable hard metal materials,
whereby one end of the generally cylindrical shape forms a convex
surface such as a dome, a rounded cone or a chisel shape involving
edges.
[0012] Conventional PCD rock removal elements, be they intended for
drag bit or roller cone bits, have been restricted to relatively
thin layers of PCD material (typically from 1 to about 2.5 mm and
rarely up to about 4 mm) formed attached to typically one side of
large, substantially cylindrical hard metal substrates in the same
high pressure high temperature processes. The required metal for
the partial re-crystallisation and sintering of the diamond
particles leading to the inter-grown polycrystalline diamond grains
is predominantly derived from and infiltrated from the hard metal
substrates. The long range infiltration of the required metal
necessary for PCD layers between 2.5 and 4 mm progressively
contributes to difficulties of producing well sintered diamond
grains.
[0013] The dominant life limiting mechanism for conventional PCD
rock removal elements or bodies involves crack propagation in the
PCD body which extends to the free surfaces of the PCD material
resulting in extremely damaging chipping and spelling behaviour. It
is believed that a governing aspect for such crack propagation is
the residual stress distribution in the PCD rock removal element or
body which results from the differential thermal contraction of the
PCD layer compared to the hard metal substrate material during the
return-to-room pressure and temperature of the manufacturing
process. Due to the conventional rock removal element or body
designs involving the PCD layers being attached to one side of the
hard metal substrates, the return-to-room pressure and temperature
in the manufacturing process causes bending distortion to occur in
the PCD layers, necessarily resulting in the residual stress
distribution spanning the PCD layers involving substantial and
significant tensile stress components. These tensile stress
components govern the direction of crack propagation. Their
particular magnitude, gradients and directional residual stress
distributions for specific designs and arrangements for PCD layers
and substrates distinguishes the poorest and the best designs.
[0014] Conventional PCD bodies comprising a thin layer of PCD
material attached during manufacturing processes to substantial
hard metal substrates also are restricted in both PCD layer
thickness and composition of the PCD material itself. PCD layer
thicknesses made conventionally are typically less than 2.5 mm,
though exceptionally up to 4 mm. These thicker PCD layers are very
difficult to make and progressively suffer from inferior structure
and properties arising from poor diamond-to-diamond bonding as a
consequence of impurity segregation and general difficulties of
long range infiltration of the catalyst/solvent metals for
sintering of the diamond particles. The compositional restrictions
of the conventional PCD layers concern a dependence of the overall
metal content of the PCD material to the diamond grain size
distribution. This is illustrated in FIG. 5 where the cobalt
content of conventional PCD material is plotted against the average
grain size of well-established conventional PCD materials. It can
be seen from this graph that the cobalt content is limited to a
band, 501, of approximate thickness 4 volume percent, where for
fine grain PCD material, e.g. of average grain size 1 micro meter,
the metal content is about 12 volume percent, decreasing for coarse
PCD material, e.g., of average grain size 20 micro meters to about
6 volume percent. Metal contents outside this band are not typical
and are very difficult to make. Moreover, the metallurgy of
conventional PCD materials is restricted to the metallurgies which
are suitable for diamond particle recrystallization and sintering,
and of viable hard metal materials, if such materials are exploited
as substrate materials. Typically and commercially, the dominant
metal in this regard is cobalt with, to a far lesser extent,
certain nickel and/or iron alloy variations of cobalt.
[0015] Thus there is a need for improved rock removal or rock
crushing elements which ameliorate or substantially overcome one or
more of the abovementioned problems or disadvantages.
SUMMARY
[0016] Viewed from a first aspect there is provided a rock removal
body for a drag bit rock drilling application comprising a
polycrystalline diamond (PCD) material volume bonded to a cemented
hard metal substrate along an interface; wherein: [0017] a. the
body has an overall body volume, and is of a right circular
cylindrical shape having a circumferential edge, and a barrel
portion, the PCD material volume being axially asymmetrically
disposed at one end of the body; [0018] b. the PCD material volume
has a thickness from the circumferential edge axially along the
surface of the barrel portion of around 3 mm or greater and a
functional working volume, the functional working volume being the
volume of PCD material progressively worn away in use during useful
life of the rock removal body to a form a final wear surface, the
functional working volume having a maximum extent such that the
final wear surface does not intersect the interface of the PCD
material volume and the substrate; [0019] c. the interface bonding
the polycrystalline diamond material volume to the cemented hard
metal substrate comprising a layer of a third material derived from
a refractory material, the third material being a metal diffusion
blocking barrier material to molten bonding material of the
substrate and molten catalyst solvent sintering aid of the PCD
material volume during formation of the rock removal body; [0020]
d. the PCD material volume comprising a plurality of inter-bonded
diamond grains having an average diamond grain size forming a
diamond network and a metallic component forming a metallic
network, and the substrate comprising a cementing metal, the
metallic component and the cementing metal being independent of one
another, independently derived, have not interacted during the high
pressure high temperature manufacturing process, are measurably
distinguishable and are pre-selected to be different with respect
to their alloy composition; [0021] e. the PCD material at least
encompasses the functional working volume and is homogeneous in
that the PCD material is spatially constant and invariant with
respect to diamond network to metallic network volume ratio,
wherein the homogeneity is measured at a scale greater than ten
times the average diamond grain size, the maximum diamond grain
size in the diamond network being less than three times the average
diamond grain size.
[0022] Viewed from a second aspect there is provided a rock removal
body for a roller cone bit rock drilling application comprising a
polycrystalline diamond (PCD) material volume bonded to a cemented
hard metal substrate along an interface; wherein: [0023] a. the
body comprises a right circular cylinder portion having an
associated radius, one end of the cylinder portion forming a
generally convex curved surface or surfaces with an apex, or one
end forming a general chisel shape where two or more flat surfaces
meet to form an apex, the PCD material volume being axially
asymmetrically disposed extending from and abutting the apex, the
cemented hard metal substrate being disposed at the opposite end of
the cylinder; [0024] b. the PCD material volume has a thickness
from the apex in the axial direction of the cylinder portion of the
body to the interface with the substrate equal to or greater than
the radius of the cylinder portion of the body, the PCD material
volume further comprising a functional working volume, the
functional working volume being the volume of PCD material
progressively worn away in use during useful life of the rock
removal body to a form a final wear surface, the functional working
volume having a maximum extent such that the maximum extent of the
functional working volume is less than the thickness of the PCD
material volume thickness; the functional working volume extending
from the apex in the axial direction; [0025] c. the interface
bonding the PCD material volume to the substrate comprising a thin
layer of a third material derived from a refractory material, the
third material being a metal diffusion blocking barrier material to
molten bonding material of the substrate and molten catalyst
solvent sintering aid of the PCD material volume during formation
of the rock removal body; [0026] d. the PCD material volume
comprising a plurality of inter-bonded diamond grains having an
average diamond grain size forming a diamond network and a metallic
component forming a metallic network, and the substrate comprising
a cementing metal, the metallic component and the cementing metal
being independent of one another, independently derived, have not
interacted during the high pressure high temperature manufacturing
process, are measurably distinguishable and are pre-selected to be
different with respect to their alloy composition; [0027] e. the
PCD material at least encompasses the functional working volume and
is homogeneous in that the PCD material is spatially constant and
invariant with respect to diamond network to metallic network
volume ratio, wherein the homogeneity is measured at a scale
greater than ten times the average diamond grain size, the maximum
diamond grain size in the diamond network being less than three
times the average diamond grain size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Examples will now be described with reference to the
accompanying drawings in which:
[0029] FIG. 1 is a schematic diagram of a conventional drag bit and
housing body;
[0030] FIG. 2 is a schematic side view of one edge of a
conventional PCD rock cutting element continuously shearing
rock;
[0031] FIG. 3 is a schematic diagram of a typical roller cone drill
bit consisting of a housing body and three roller cone
structures;
[0032] FIG. 4 is a cross-section of a dome shaped conventional PCD
rock crushing element consisting of a thin layer of PCD material
bearing on and crushing rock;
[0033] FIG. 5 is a graph of the cobalt content of conventional PCD
material plotted against the average grain size of well-established
conventional PCD materials;
[0034] FIG. 6 is a schematic cross-section of a right cylindrical
rock removal body intended for use in drag bit rock drilling
wherein the dotted line indicates the final position of a wear scar
formed during rock drilling application at end of life of the rock
removal element or body;
[0035] FIGS. 7a, 7b and 7c are half cross-sectional schematic
diagrams of examples giving the main characteristics of the
residual stress distribution in a PCD material volume thickness of
2, 5 and 8 mm, respectively;
[0036] FIGS. 8a, 8b and 8c are schematic cross-sectional diagrams
which illustrate a generally convex curved surface or surfaces
which can take a hemispheroidal form, either a prolate
hemispheroidal, oblate hemispheroidal or a hemispherical form,
respectively;
[0037] FIG. 9a is a schematic cross-sectional diagram of an example
curved surface which takes the form of a cone with a rounded apex,
and FIG. 9b shows an example of a general chisel shape which forms
an apex;
[0038] FIGS. 10a, 10b, 10c and 10d are axial cross-sections of an
example rock removal body for use in a conventional roller cone bit
design, showing the zones of principal residual stress
distinguished by grey shading where the thickness of the PCD
material layer are 2, 8, 10 and 16 mm, respectively;
[0039] FIGS. 11a and 11b indicate the positions of the dominant
principal tensile residual stress maxima in the PCD material volume
and the cemented hard metal substrate where FIG. 11a represents
examples for drag bit applications and FIG. 11b represents the
examples for roller cone bit applications;
[0040] FIG. 12 shows an example of a PCD rock removal body intended
for drag bit applications, where the PCD material volume comprises
two or more layers of differing PCD material and a half
cross-section of the body is shown where the principal residual
stress distribution is presented by a series of grey shaded volumes
which are delineated by contour lines of equal stress;
[0041] FIG. 13 is a set of examples comprising one homogeneous PCD
material and the cemented hard metal substrate comprising two
layers of differing material and illustrates the residual stress
benefits of employing discrete layers of differing cemented hard
metal carbide materials; and
[0042] FIG. 14 shows the residual stress benefits when the two
layered arrangement of differing PCD materials of FIG. 12 are
combined with the two layer arrangement of differing tungsten
carbide cobalt hard metal of FIG. 13.
DETAILED DESCRIPTION
[0043] As shown in FIG. 6, the rock removal bodies of examples
described herein may comprise a right circular cylindrical overall
shape with a PCD material volume 601 axially asymmetrically
disposed at one end of the cylindrical body, with a right
cylindrical cemented hard metal carbide substrate 602 disposed at
the opposite end. The cemented hard metal substrate 602 ensures
that the standard custom and practice of braze technologies
developed for drag bit manufacture may be applied in substantively
unaltered form. Moreover, there should be sufficient cemented hard
metal substrate free surface area to provide adequate bond strength
to the braze layer or engagement, this consideration implies a
chosen minimum size of substrate for each design of the examples
described herein.
[0044] FIG. 6 is a schematic cross section of a right cylindrical
rock removal body intended for use in drag bit rock drilling. A
layer of PCD material 601 is separated from a cemented hard metal
substrate, 602, by a thin layer of material, 603, which is extant
from the use of a barrier layer material used to separate the PCD
material volume and the cemented hard metal substrate during
manufacture. The dotted line 604 indicates the final position of a
wear scar formed during rock drilling application at end of life of
the rock removal element or body. A part of the circumferential
edge, 605, indicates the part of the composite rock removal body
which first is made to bear on the rock strata. The volume of
material 606 between the circumferential edge 605 and the dotted
line 604 is the volume of PCD material which is progressively worn
away during use and will subsequently be referred to as the
functional working volume. The remainder of the volume of the
composite body outside 606 will subsequently be referred to as the
functional support volume. The functional support volume is extant
at end of life of the body and comprises the part of PCD material
volume 601 left after end of life together with the barrier layer
603 and hard metal substrate 602. The thicknesses of the PCD
material layer, 601, and the barrier layer material, 603, and the
length of hard metal substrate, 602, are designated by 607, 608 and
609, respectively. The interfacial thin layer of material 603
separating and bonding the PCD material volume 601 and the
substrate 602 may form a planar interface or a non-planar curved
surface. Planar in this context means that the interface between
the PCD bonding boundary layer and the cemented hard metal
substrate is substantially flat and substantially parallel to the
base of the cylindrical rock removal body, that being the cemented
hard metal substrate. The interfacial layer 603 alternatively may
not be flat but may be made up of a curved surface or surfaces
usually arcuate in regard to the flat end of the cylindrical body.
This will be referred to as non-planar interfaces. In some
examples, the outer free surface of the cemented hard metal
substrate 602 is in the form of a right circular cylinder. The
layer of PCD material 601 will be a cylindrical layer when the
interfacial thin layer of material 601 is planar.
[0045] The presence of a cemented hard metal substrate 602 bonded
in an axially asymmetric manner to the PCD material volume 601
during the high pressure high temperature manufacture of the PCD
material volume causes residual stress distributions in both the
PCD and cemented hard metal material volumes. The residual stress
distributions are due to bending effects caused by differential
expansion and contraction of the PCD and cemented hard metal
material volumes during the return-to-room temperature and pressure
at the end of the high pressure high temperature manufacturing
process. These differential dilations are a result of the elastic
modulus and thermal expansion properties of the PCD and cemented
hard metal carbides being significantly different. In the
experience of the inventors of the current application, the
residual stress distribution in PCD, hard metal composite rock
removal elements, in particular the tensile residual components in
the PCD material volume, are the dominant aspects which may
determine the useful life of such rock removal bodies. This is
understood to be due to the fact that, typically, crack related
failures such as chipping and spelling are the dominant life
limiting considerations.
[0046] In conventional PCD cutters where the required metal for the
liquid phase sintering of the PCD particulate network of the PCD
material volumes is derived from long range infiltration of molten
cementing metals of the carbide substrate, the residual stress
distribution in the PCD material volume is of particular highly
significance in this regard. The long range infiltration of the
required metal into the PCD volume results in the restriction of
the general thickness of the PCD material volume to typically less
than 3 mm.
[0047] Some examples described herein provide for means whereby
there is no such molten metal infiltration related limitation on
PCD material volume dimensions and thicknesses. In order to provide
a relatively unrestricted scale to the PCD material volume
dimensions, the metal required for the PCD material may be
independently derived and isolated from the cementing metal of the
hard metal substrate. PCD material volumes of any general simple
shape, up to dimensions limited by the high pressure high
temperature apparatus available, may be made by providing the
necessary metal for the PCD material from a starting mass of
particulate diamond intimately and homogeneously combined with
metallic particles. Thus, the metallic component of the PCD
material volume and the cementing metal of the hard metal substrate
are independent of one another, independently derived and have not
interacted during the high pressure high temperature process.
Moreover, in the rock removal elements of the examples described
herein, the metal components of the PCD material volume and the
hard metal substrate are measurably different and pre-selected to
be different in their elemental composition.
[0048] The molten binder metal of the hard metal substrate may be
precluded from infiltrating into the polycrystalline diamond volume
of the composite and an example of a means of achieving this
separation and isolation of the metallurgy of the PCD volume and
the hard metal substrate volume is to provide a barrier layer 603
between the said volumes which is capable of preventing significant
cross contamination of the molten metals of the substrate and PCD
material volumes. Barrier layers which may operate in this way may
comprise materials which have significantly higher melting points
than the catalyst/solvent metals for the PCD material and also the
binder metal of the hard metal substrate. In addition, such metals
may alloy and react slowly with the molten catalyst/solvent metals
for the PCD materials and the molten binder metal for the hard
metal substrate. This latter point may assist in providing for
sufficient barrier behaviour and also bonding behaviour with both
the PCD material and the substrate material. Examples of metals
which may satisfy these behaviours may comprise the refractory
metals including tantalum, vanadium, niobium, molybdenum, zirconium
and their alloys.
[0049] Certain ceramic materials such as nitrides, borides and
carbides may also fulfil the required criteria. Some examples of
such ceramics are tantalum nitride, titanium nitride, aluminium
nitride, silicon nitride and mixed nitrides. In some examples, a 50
to 500 micro meter thick continuous zirconium metal barrier layer
or bonding layer may be used. In some examples, the barrier layer
may comprise a 50 micro meter thick tantalum metal or zirconium
metal layer. Also, in some embodiments, a thin layer of
nitrides/borides and/or carbides of the elements of groups IVa, Va
and/or VIa of the periodic table and B, Si and Al, including, for
example, TaN, TiB.sub.2, ZrB.sub.2, AIN, Si.sub.3N.sub.4, AIB.sub.2
and ZrN, refractory metals, solids solutions, e.g., (Ti, Al)N and
mixtures of these, may be used and may be applied using physical
vapour deposition (PVD) or chemical vapour deposition (CVD)
techniques. In some examples, the barrier layer between the PCD
volume and hard metal substrate may comprise a continuous titanium
nitride (TiN) layer, greater than around 3 micro meters in
thickness. These thin barrier layers may have particular utility
when the interface geometry between the PCD layer and substrate has
a non-planar geometry.
[0050] Thus, examples may comprise an interface bonding the
polycrystalline material volume to the cemented hard metal
substrate, which is comprised of a thin layer of a third material
derived from a refractory material which acts as a metal diffusion
blocking barrier material to the molten cementing material of the
hard metal substrate and the molten catalyst sintering aid of the
polycrystalline diamond material during the high pressure high
temperature process.
[0051] The metallic component of the PCD material volume and the
cementing metal of the hard metal substrate are independent of one
another as a result of being prevented from interacting with one
another during the high pressure high temperature process due to
the presence of the barrier material layer.
[0052] This independence of the metallurgy of the PCD material
volume and the cementing metal of the hard metal substrate may
assist in allowing each of these metallic components to be
independently pre-selected in regard to particular desired
composition and properties for each of the PCD material volume and
hard metal substrate. This is in contrast to much of the
conventional prior art PCD where the metal of the PCD material
volume is wholly or in part derived from the cementing metal of the
hard metal substrate. For example, it may be desired to exploit a
corrosion resistant grade of tungsten carbide hard metal based upon
the cementing metal. This corrosion resistance is often and
typically achieved by alloying the cobalt cementing metal with
elements such as nickel and chromium, or completely replacing it
with a more corrosion resistant alloy. These alloying agents may
well not be ideal or desired components of the metal of the PCD
material volume. In this regard, elements such as chromium and
other stable carbide forming metals will always and necessarily
form precipitated carbides in metal network of the PCD material
volume. Such precipitated carbides may well undesirably alter the
properties of the PCD material volume.
[0053] By contrast, some examples described herein may allow for
the exploitation of a greatly expanded range of substrate materials
without suffering from such potentially undesired metallurgies of
the PCD material volume. A further example may well be the use of
titanium carbide cemented with nickel hard metal material for the
substrates while exploiting well established simple cobalt PCD
material volume metallurgy. Thus, greatly expanded material design
capabilities may be achievable in comparison with the conventional
prior art where the metallurgies of the PCD material volume and the
cemented hard metal substrate are co-dependent.
[0054] Thus, in some examples, the metallic component of the PCD
material volume and the cementing metal of the hard metal substrate
are independent of one another, are independently derived, have not
interacted during the high pressure high temperature process, are
measurably distinguishable and are pre-selected to be different
with respect to the alloy composition. Since a role of the metal of
the PCD material volume is to act as a molten catalyst/solvent for
diamond recrystallization from solution, the metallic component of
the PCD material volume may be a high carbon content alloy of
transition metals which may be able to act as catalyst/solvent for
diamond recrystallization from solution. These include, for
example, transition metals such as cobalt, nickel, iron, manganese
and their alloys. High carbon content cobalt may be a
catalyst/solvent for the formation of the PCD network. In contrast,
the cementing metal of the hard metal substrate will have acted as
a liquid phase for the sintering of the carbide hard material. Such
cementing metals will therefore tend to be alloys containing the
hard metal carbide and the metallic element or elements of the
carbide in solid solution. Typical of such cementing metals is, for
example, cobalt with tungsten in solid solution for tungsten
carbide cobalt based hard metal or nickel with titanium in solid
solution for titanium carbide nickel based hard metal. Even if both
the metal component of the PCD material volume and the cementing
metal of the hard metal substrate are dominated and substantially
the same metallic element, such as cobalt, they will be measurably
distinguishable in such examples. The former will be a high carbon
cobalt alloy as compared to a cobalt tungsten alloy for the latter.
The metallic component of the PCD material volume and the cementing
metal of the hard metal substrate of some examples may be
preselected to be different with respect to their alloy
composition. The metal component of the PCD material volume may be
shown to be different in alloy composition using standard
analytical techniques known in the art. These techniques include
Energy Dispersive Analysis (EDS) on a Scanning Electron Microscope,
X-Ray Diffraction and Wet Chemical Analysis.
[0055] It has been observed in general drag bit subterranean rock
drilling that when the life of cylindrical rock removing elements
such as those schematically depicted in FIG. 6 is not determined by
premature chipping and spelling, the typical size of the functional
working volume at end of life is such that the remaining wear scar
extends down the barrel of the cylindrical surface by about 3 mm.
This is indicated in FIG. 6 by the intersection of the dotted line
604 with the barrel of the cylindrical body. In such circumstances,
the life of the rock removal body has been determined by normal
wear behaviour and not by macroscopic fracture. This is a desirable
situation as macroscopic fracture such as in chipping and spalling
is a variable uncontrolled premature failure. However, it must be
emphasized that in the inventors' experience, the conventional
prior art rock removal element designs have their lives primarily
determined by chipping and spalling macroscopic crack related
phenomena. Examples described herein may assist in providing a
means by which the desirable normal wear dominated behaviour may be
approached. In this regard, the residual stress distribution of any
given example will be of primary consideration. More specifically,
some examples are created which are characterised by lowering
tensile stress maxima, displacing these maxima from the environs of
the functional working volume and the reduction of tensile stress
gradients in and close to the functional working volume. In this
way the probability of macroscopic crack propagation in use may be
reduced.
[0056] The commonest conventional rock removal elements, commonly
known as cutters, are all generally right circular cylinders with
the PCD material volume dimension at the barrel being typically
around 2.5 mm and rarely and exceptionally around 3 to 4 mm. The
diameter and length are usually selected according to the
specifications given in the Table 1 below.
TABLE-US-00001 TABLE 1 Configuration Diameter (mm) Length (mm) 1308
13 8 1313 13 13 1612 16 12 1616 16 16 1912 19 12 1916 19 16
[0057] The examples described may be directed at any of the
standard configurations. The 1616 configuration will be used to
exemplify various features, which may be applied to all of the
configurations in Table 1.
[0058] The PCD material volume may be made to any predetermined
dimensions. In the context of the 1616 example, where also a flat
planar interfacial boundary is specified, the PCD material volume
therefore may be chosen to be of any thickness within the
constraints of the overall length. FIGS. 7a, 7b and 7c are half
cross-sectional schematic diagrams giving the main characteristics
of the residual stress distribution for a 1616 configuration and
comparing a PCD material volume thickness of 2, 5 and 8 mm,
respectively. The stress distribution provided gives information of
the principle residual stress and thus no information is provided
at any given position of the direction of the stress. The residual
stress distribution information was generated using an ABACUS
Finite Element Analysis (FEA) computer package well known in the
art and general engineering practice. The properties of the PCD
material and the cemented hard metal material used for the analysis
were as follows. The elastic modulus of the PCD material and the
cemented hard metal material used in the analysis were 1020 GPa and
550 GPa, respectively. The linear coefficients of thermal expansion
of the PCD material and the cemented carbide material used in the
analysis were 4.01 ppm .degree. K.sup.-1 and 5.5 ppm .degree.
K.sup.-1, respectively. The line 701 represents the planar
interfacial boundary thin layer of third material derived from the
refractory barrier material. For the purposes of this analysis no
detail is included with regard to this thin boundary bonding layer,
as the general semi-quantitative and qualitative character of the
residual stress distribution in both the PCD material and the
cemented hard metal substrate is not significantly altered by such
detailed information. This thin boundary bonding layer may however
operate to locally graduate the stresses across the boundary. The
dotted line 702 represents the position of the final wear scar
surface, i.e., the final extent of the functional working volume at
end of life. Thus, the material progressively worn away during use
extends from the line 702 to a position on the circumferential edge
of the PCD material volume, 703, which indicates the point of first
contact of the rock removal element or cutter at commencement of
use.
[0059] As already stated, in the experience of the inventors, the
dimension of the functional working volume at end of life is chosen
to be around 3 mm vertically down the barrel of the cylindrical
surface.
[0060] The angle 704 the final wear scar 702 makes with respect to
the vertical of the cylindrical barrel is dependent upon the chosen
rake angle in relation to the rock surface. This angle is chosen to
be 20.degree. for the purpose of this analysis and is typical of
what is used in practice. This means that the extent of the
functional working volume at end of life radially from 703, along
the top flat surface, will be about 1.1 mm.
[0061] The lines labelled 705 represent principle tensile
iso-stress contour lines in the cemented carbide substrate. Between
this line and the base and barrel free surfaces of the substrate,
the volume is occupied by a principle tensile stress field of very
low magnitude. Between 705 and the line representing the barrier
layer 701, in the direction of the barrier 701, there is a
principal tensile stress field increasing in magnitude with an
increase in stress gradient becoming more and more intense as the
barrier layer is approached. The line 706 represents an
intermediate principal iso-stress contour line.
[0062] The dotted line 707 indicates the position of the maximum
principal tensile stress in the substrate material immediately
below the barrier layer 701. Note that at all positions in the
cemented hard metal carbide the principal stresses are tensile. The
line 708 in the PCD material volume represents the zero stress
contour line which separates the hatched volume of PCD material
which is in compression from a general tensile field occupying the
remainder of the PCD material volume. Two positions of principal
tensile stress maxima are indicated by 709 and 710, respectively.
The principal stress tensile maximum 709 occupies a position at the
circumferential barrel surface of the PCD material volume slightly
above the barrier layer 701. This principal stress tensile maximum
709 is dominated by an axial tensile stress. The principal stress
tensile maximum 710 occupies a position on the flat top free
surface of the PCD material volume. This principal stress tensile
maximum, 710, is dominated by a radial tensile stress.
[0063] In FIG. 7a where the PCD material volume is 2 mm thick, it
should be noted that the line dotted line 702, representing the
final wear scar at end of life intersects the boundary layer 701
and extends into a highly tensile region of the cemented hard metal
substrate. Moreover, the volume of material between the dotted
lines 702 and 703, namely the functional working volume,
encompasses the tensile maximum stress 709. So, during the
progressive wearing away of the functional working volume during
application, the wear scar moving parallel towards line 702 will
interact with the axial tensile maximum 709, and followed by
interacting with the highly tensile location below the barrier
layer 701 in the cemented hard metal substrate, 707.
[0064] It has been observed by the inventors that, when a wear scar
interacts with such tensile stress maxima and high tensile stress
gradients, macroscopic cracks propagate behind the wear scar in the
PCD material volume guided by the general residual stress fields
and gradients. Such cracks may lead to chipping and spalling and
premature end to the useful life of such rock removing elements or
cutters. The PCD construction depicted in FIG. 7a may therefore be
undesirable in some applications because of the final wear scar
position 702 crossing the boundary 701 and extending into the
cemented hard metal substrate.
[0065] In comparison, FIG. 7b illustrates an example where the PCD
material volume thickness is 5 mm. Note that the functional working
volume is invariant with respect to position and scale. In this
example, the final wear scar position 702 does not cross the
boundary 701 and thus does not extend into the cemented hard metal
substrate. Moreover, the functional working volume in example of
FIG. 7b does not encompass the tensile stress maximum 710 and
occupies a volume therefore of greatly reduced residual stresses
and gradients. Such examples may be more favourable in that the
probability of macroscopic crack propagation to free surfaces
leading to chipping and spalling may now be significantly
reduced.
[0066] A distinguishing factor between the example of FIG. 7b and
the PCD construction of FIG. 7a is the crossing and interaction of
the final wear scar 702 with the barrier boundary layer 701. In
general, examples where the final wear scar position 702 does not
cross and interact with the boundary layer 701 may be favoured. The
functional working volume is considered to be invariant in the use
of these drag bit examples, such that the extension of the final
wear scar 702 down the circumferential barrel surface of the
cylindrical cutter is about 3mm, so examples where the thickness of
the PCD material volume from its circumferential edge axially along
the curved barrel of the cylinder is 3 mm or greater are a feature
of some of the examples described herein.
[0067] The example depicted in FIG. 7c where the PCD material
volume thickness is 8 mm and the cemented hard metal substrate is
also 8 mm indicates a further improvement over the embodiment of
FIG. 7b, when considering the residual stress distribution
character in the PCD material volume, in that both the tensile
maxima 709 and 710 are further displaced from the position of the
functional working volume. Moreover, the tensile stress gradients
in the functional working volume are progressively reduced as the
thickness of the PCD material volume is increased. This may be
further illustrated by considering the arrows 711 and 712 which
represent the direction of the tensile stress gradients in the
axial and radial directions, respectively, in the functional
working volume.
[0068] Table 2 gives the estimated values of the average principal
tensile stress gradients, 711 and 712. It may be seen that these
estimates indicate that, as the PCD material volume thickness
increases from 2 to 8 mm, the tensile stress gradient 711 is
progressively reduced by an order of magnitude and that the tensile
stress gradient 712 is progressively reduced by about a factor of
4. This analysis, therefore, indicates that a less damaging tensile
residual stress distribution in the functional working volume may
progressively develop as the PCD material volume thickness
increases from around 3 mm.
TABLE-US-00002 TABLE 2 PCD material Stress Stress Construction
volume thickness gradient, 711 gradient, 712 of FIG. No. (mm)
(MPa/mm) (MPa/mm) 7a 2 250 60 7b 5 60 30 7c 8 10 15
[0069] The trend of beneficial displacement of the tensile stress
maxima, 709 and 710, at the free surface of the PCD material
volumes, progressively becoming more and more remote from the
functional working volume may continue as the PCD material volume
thickness becomes larger and larger. However, as the PCD material
volume thickness becomes larger, the principal tensile stresses in
the cemented hard metal substrate may increase in magnitude and
extent. This may be seen by comparing the maximum principal tensile
stress 707 for FIGS. 7a, 7b and 7c as the PCD material volume
thickness changes from 2 to 5 to 8 mm, respectively. Note that the
extent of this maximum principal tensile stress progressively
expands and spreads along the boundary layer 701. This maximum
principal tensile stress, 707, is dominated by primarily tensile
stress in the hoop direction, i.e., along the circumferential
direction. Cracks that form and extend into this region will then
tend to split the hard metal substrate diametrically. This was
indeed observed for situations where the PCD material layer was
large in comparison with the cemented hard metal substrate.
[0070] Moreover, it may also be seen from the comparison of FIGS.
7a, 7b and 7c that, as the thickness or length of the hard metal
substrate becomes reduced, the principal tensile stress gradient,
extending from the base of the substrate towards the interfacial
boundary 701, significantly increases. This is a progressively
unsatisfactory situation which further contributes to the
probability of crack propagation in the cemented hard metal
substrate leading to failure of the rock removal element.
[0071] Experientially, the inventors have found that the occurrence
of diametrical splitting of the hard metal substrate may be greatly
reduced when the volume of the PCD material is less than 50 percent
of the overall rock removal body volume, i.e., when the ratio of
the PCD material volume thickness to the cemented hard metal
substrate length or thickness measured from the circumferential
edge of the body along the curved barrel surface of the cylinder is
less than 1.0.
[0072] For a 16 mm diameter and 16 mm long right circular cylinder
as illustrated FIGS. 7a 7b and 7c, this may be expressed such that
the PCD material volume is a cylindrical layer with thickness 3 mm
or greater and the combined thickness of the boundary layer and the
cemented hard metal substrate is 8 mm or greater, the interfaces
between the PCD material volume boundary and cemented hard metal
substrate being flat, planar and parallel to the base of the PCD
rock removal body. This means that the thickness of the PCD
material volume layer is between 3 mm and 8 mm for these
constructions.
[0073] More generally, for the configurations listed in Table 1,
encompassed by the diameter of the cylindrical body being in the
range 12 to 20 mm and the overall length of the body 11 to 20 mm,
the PCD material volume is a cylindrical layer with thickness 3 mm
or greater and the combined thickness of the bonding boundary layer
and the cemented hard metal substrate is 8 mm or greater, the
bonding interface between the PCD material volume and the cemented
hard metal substrate being flat, planar and parallel to the base of
the cylindrical rock removal body.
[0074] One of the advantages and benefits of the PCD of some of the
examples, is that the resulting PCD material exhibits a very high
degree of homogeneity in that the diamond network to metallic
network volume ratio is spatially constant and invariant at and
above a scale directly related to the diamond grain size. This may
be achieved by generating a starting particulate mass of diamond
particles homogeneously mixed with an accurately determined amount
of metal particles such that the metal is always smaller than the
diamond particle sizes. The methods may involve suspending the
diamond particles in a liquid and nucleating and growing precursor
compound(s) for the required metals on the surfaces of the diamond
particles. The precursor compound(s) are then conveniently
converted to pure metals attached to the diamond surfaces by heat
treatment in reducing furnace environment. Specifically, the
homogeneity obtainable in the resulting PCD material by such
methods may be demonstrated and measured at a scale greater than
ten times the average diamond grain size. A further constraint on
the diamond grain size distribution in the context of such
homogeneous materials is that the maximum grain size be less than
three times the average diamond grain size. Such homogeneous PCD
materials may have best utility if they at least encompass the
functional working volume. Homogeneity in this regard may allow the
avoidance of local stress inducing inhomogeneity-based defect
structures to occur. In turn this may allow the full exploitation
of the residual stress minimizing aspects.
[0075] Thus, the PCD material in some of the examples that at least
encompasses the functional working volume is homogeneous in that it
is spatially constant and invariant with respect to diamond network
and metallic network volume ratio, wherein the homogeneity is
measured at a scale greater than ten times the average grain size,
the maximum diamond grain size being less than three times the
average diamond grain size.
[0076] The residual stress related criteria applied to the examples
may allow the probability of macroscopic crack related behaviour,
such as chipping and spelling, to be so reduced that they become of
secondary consideration. The primary consideration for the
performance of such examples intended for drag bit applications may
now be considered to be normal wear behaviour during the rock
removal application. PCD material compositions and structures which
exhibit improved wear resistance may then be favourably
exploited.
[0077] It is generally known in the art that high wear resistance
is associated with finer diamond grain sizes, and also with high
diamond concentration, i.e., low metal content. In the conventional
prior art where the required metal for the sintering of the PCD
material is derived from long range infiltration from a cemented
hard metal substrate, finer diamond grain sizes are invariably
associated with high metal content. The diamond grain size and
metal content are not independently pre-selectable. For example, in
the conventional prior art, when the average grain size is chosen
in the range ten to one micro meters, the typical metal contents
progressively increase from about nine volume percent to about
twelve volume percent. Experientially, in such conventional prior
art, metal contents as low as five volume percent are not
obtainable for PCD materials with average diamond grain sizes less
than ten microns.
[0078] By contrast, in some examples, the diamond grain size
distribution and the metal content are independently pre-selected.
Fine grained PCD material less than ten micro meters average grain
size with a metal content between five and nine volume percent may
be utilized to assist in exploiting high wear resistant behaviour
of the PCD material in the functional working volume.
[0079] To enable the examples to be used in largely unaltered
roller cone bit designs and custom and practice, the rock removal
bodies of the examples intended for roller cone bit applications
may comprise a body comprising a right circular cylinder body with
one end extending to an apex, with the PCD material volume being
axially asymmetrically disposed extending from or abutting the
apex, the cemented hard metal substrate being disposed at the
opposite cylindrical end. The apex may be formed by a generally
convex curved surface or surfaces. Alternatively, the apex may be
formed by a general chisel shape where two or more flat surfaces
meet to form the apex.
[0080] The generally convex curved surface or surfaces may take a
hemispheroidal form, for example, either a prolate hemispheroidal,
oblate hemispheroidal or a hemispherical form, respectively. FIGS.
8a, 8b, 8c are schematic cross-sectional diagrams which illustrate
such examples, respectively. The PCD material volumes, cemented
hard metal substrates with a thin layer of bonding material are
labelled 801, 802 and 803, respectively. The PCD material volume
801 extends from and abuts the apex 804. Note that in these
examples, the interfacial bonding material layer 803 separating the
PCD material 801 and the cemented hard metal substrate intersects
the free surface of the body in the cylindrical barrel surface
below the shoulder 805, this being defined as the line of departure
of the barrel cylindrical surface extending into the generally
convex curved surface. The generally curved surface or surfaces may
take the form of a cone with a rounded apex where the radius of the
rounded apex is about a quarter to a half of the radius of the
cylindrical part of the body. This is illustrated in the schematic
cross-sectional diagram FIG. 9a where the PCD material volume,
cemented hard metal substrate with a thin layer of bonding material
are labelled 901, 902 and 903, respectively. The PCD material
volume, 901, extends from the rounded apex 904.
[0081] Yet another example is illustrated in FIG. 9b, which shows
an example having a general chisel shape which forms an apex. The
PCD material volume and cemented hard metal substrate with a thin
layer of bonding material are labelled 901, 902 and 903,
respectively. The illustrated chisel shape comprises a conical
surface, 905, with a rounded apex, 904, modified by two symmetrical
flat inclined surfaces, 906, which meet at an apex, 904. The
interfacial bonding material layer, 903, separating the PCD
material volume, 901, and the cemented hard metal substrate, 902,
intersects the free surface of the body in the barrel below the
shoulder, 907, this being defined as the line of departure of the
barrel cylindrical surface extending into the conical curved
surface.
[0082] In FIGS. 8a to c and 9a and 9b, the interfacial bonding
material layer, 803 and 903, is a thin layer of material which is
extant from the use of a barrier layer material used to separate
the PCD material volume, 801 and 901, and the cemented hard metal
substrate, 802 and 902, during manufacture. The barrier layer
material assists in isolating the molten cementing metal of the
hard metal substrate from the molten catalyst/solvent metal of the
PCD material volume during the high pressure high temperature
manufacturing process.
[0083] The cemented hard metal substrate assists in enabling the
standard custom and practice of braze technologies developed for
roller cone bit manufacture to be applied in substantively
unaltered form. Moreover, a chosen minimum size of substrate for
each design of the examples may assist in enabling there to be
sufficient cemented hard metal substrate free surface area to
provide adequate bond strength to the braze layer for
engagement.
[0084] Prior art rock removal elements utilizing PCD for roller
cone bit applications conventionally exploit a thin layer of PCD
material, typically 1.0 to 2.0 mm thick, forming a shell at a
convexly curved surface or surfaces. This is illustrated in FIG. 4.
By contrast, the examples described herein are not restricted to
thin layers of PCD material and may exploit PCD material volumes
which may occupy large volumes adjacent to and abutting the apices
of convexly curved surface or surfaces, conical surfaces or general
chisel surfaces.
[0085] In FIGS. 8a to 9b, the dotted lines 806 and 908 indicate the
final position of a wear scar formed during rock drilling
application at end of life of the rock removal element or body. The
apices, 804 and 904, of the PCD material volumes, 801 and 901,
indicate the part of the rock removal body which is first made to
bear on the rock strata. The volumes of PCD material 807 and 909
between 804 and 904 and the dotted lines 806 and 908, respectively,
are the volumes of PCD material which are progressively worn away
during use in the rock removal application. These volumes, 807 and
909, will subsequently be referred to as the functional working
volumes. The remainder of the volume of the composite bodies
outside the volumes 807 and 909, respectively, will subsequently be
referred to as the functional support volumes. The functional
support volumes are extant at end of life of the body and comprise
the part of PCD material volumes, 801 and 901, left after end of
life together with the interfacial layers, 803 and 903, and the
cemented hard metal substrates, 802 and 902.
[0086] For each of the examples illustrated in FIGS. 8a to 9b, the
thicknesses of the PCD material volumes, 801 and 901, is defined as
the distance from the apices 804 and 904 in the axial direction
along the axis of the body to the interfacial bonding barrier
layer, 803 and 903, respectively.
[0087] The thin interfacial bonding layers, 803 and 903, may be
flat and parallel to the circular cylindrical end of the substrates
as illustrated. Alternatively, the thin interfacial layers 803 and
903 may be generally arcuately curved in regard to the flat end
free surface of the substrate. The arcuate nature may be convex in
regard to this free surface of the substrate.
[0088] Thus some examples may comprise an interface bonding the PCD
material volume to the cemented hard metal substrate comprising a
layer of third material, for example a thin layer, derived from a
refractory material which acts as a metal diffusion blocking
barrier material to the molten bonding material of the hard metal
substrate and the molten catalyst solvent sintering aid of the PCD
material during the high pressure high temperature manufacturing
process.
[0089] Rock removal elements in roller cone bit applications
operate by predominantly a crushing action by indentation on the
rock surface. In such applications, therefore, it is necessary that
the rock removal elements bearing on the rock have high compressive
strength. Typical roller cone bit designs employ conical rollers
with protruding rock removal elements inserted into the surface of
the rollers. During drilling, the conical rollers roll around the
surface of the rock so that the apices of the rock removing
elements are cyclically brought to the bear on the rock surface.
This cyclical rotary action, therefore, always involves a degree of
impact loading to which the rock removal elements are exposed close
to and at the apices of these bodies. Cemented hard metal rock
removal elements have been traditionally used in this application
in that they have adequate strength and impact resistance
properties for such crushing actions particularly for soft rock
formations. Cemented hard metal rock removal elements however are
somewhat inadequate in respect to their wear resistance properties
in such applications and suffer from often unfortunate excessive
wear which can limit their usefulness. The systems of the prior art
conventionally comprise a relatively thin PCD layer at the apices
of cemented hard metal rock removal elements in an attempt to
mitigate such wear resistance inadequacies by providing greatly
improved wear resistance at the apices. However, these limited
thicknesses of PCD material (up to about 1 mm) do not provide
significant improvements in strength of the rock removal elements
and may suffer from easy chipping and spelling due to the
inevitable high tensile residual stresses in the PCD layers. The
present applicants have appreciated that such stresses are a
consequence of bending effects resulting from the differential
shrinkage of PCD layers or volumes bonded to cemented hard metal
substrates during manufacture.
[0090] The thin PCD layers of the conventional structures usually
involve functional grading to deal with local high interfacial
stresses. This conventional prior art may thus be viewed as using
PCD to provide an enhanced wear resistance to the roller cone
bullet which would still be dominated by the compressive properties
of the carbide. In contrast, some examples described herein exploit
the superior compressive strength of PCD over carbide by using
large PCD material volumes and therefore may assist in enhancing
the wear resistance of the PCD.
[0091] In some examples, the substantial volumes of PCD material
may occupy at least the functional working volume. Thus the PCD
material volume may provide the required strength and impact
resistance for the crushing action of the rock removal element. The
general bulk mechanical properties of homogeneous, well-sintered
PCD materials may be far superior to general cemented hard metal
materials for these purposes. Specifically, the hardness of PCD
materials may be, in some examples, be two to five times greater
than typical cobalt cemented tungsten carbide hard metals typically
used in roller cone bit drilling applications. This means that the
mechanical wear resistance of the PCD of some of the examples, may
be greatly superior to such cemented hard metals, and the measured
compressive strength of PCD material grades (greater than 6700 MPa)
may be greater than those obtained for most cobalt cemented
tungsten carbide hard metals (eg in the range 3500 to 5500 MPa).
The fracture toughness of the PCD materials of some of the examples
may be in the range 9 to 10.5 MPa.m.sup.-0.5, which is high for
such a hard material. Thus, where the examples exploit large bulk
volumes of PCD material, they may exhibit, due to this combination
of properties, very good behaviour in this application which may be
far better than typical cemented hard metals.
[0092] To assist in enabling the bulk properties of PCD materials
to be exploited, the PCD material volume in some examples must be
sufficiently large, and avoid thin layers such as those exploited
in the typical prior art PCD. Moreover, large pieces of PCD
material which have an increase of cross-sectional area at right
angles to the direction of the applied forces during the crushing
action may benefit from the concept of massive support as taught by
P W Bridgman.sup.2 . Some of the examples described herein for
roller cone drilling applications have this geometry as the PCD
material volumes extend from an apex and have a general convex
nature. These examples, may therefore enjoy the benefits of the
high rigidity of PCD materials providing massive support to their
apices when they are bearing upon and crushing the rock. The very
high rigidity of such PCD materials may be superior to those
exhibited by general cemented hard metals in these
applications.
[0093] For roller cone drilling general applications, in some of
the examples, the thickness of the PCD material volume from the
apex in the axial direction of the cylindrical part of the body to
the interface with the cemented hard metal substrate is equal to or
greater than the radius of the right circular cylindrical body. The
maximum extent of the functional working volume extending from the
apex in the axial direction may be less than the PCD material
volume thickness. This assists in achieving a minimum thickness of
PCD material volume, and for a minimum volume of PCD material
relative to the overall rock removal body volume.
[0094] The examples described may comprise a cemented hard metal
substrate. To assist in enabling relatively large bulk pieces of
PCD material to be made bonded to cemented hard metal substrates
during manufacture, it may be advantageous for the molten cementing
metal of the hard metal substrate to be prevented from interacting
with the molten catalyst/solvent metal/s necessary for the
sintering of the PCD material volume. As previously explained in
the context of examples for drag bit applications, refractory metal
layers or certain ceramic layers may be used as metal diffusion
blocking barriers during the manufacture of PCD material bonded to
cemented hard metal substrates.
[0095] For roller cone bit applications, the interface bonding the
PCD volume to the cemented hard metal substrate may comprise, for
example, a thin layer of a third material derived from the
refractory material which acted as a metal diffusion blocking
barrier material to the molten bonding material of the hard metal
substrate and the molten catalyst sintering aid of the PCD material
during the high pressure high temperature manufacturing process.
Thus, the metallic component of the PCD material volume and the
cementing metal of the hard metal substrate may be independent of
one another, may be independently derived, have not interacted
during the high pressure high temperature process, may be
measurably distinguishable and may be pre-selected to be different
with respect to the alloy composition.
[0096] As discussed above, one of the potential advantages/benefits
of the PCD of the examples, may be that the resulting PCD material
exhibits a very high degree of homogeneity in that the diamond
network to metallic network volume ratio is spatially constant and
invariant at and above a scale directly related to the diamond
grain size. To assist in achieving this, a starting particulate
mass of diamond particles is generated which is homogeneously mixed
with an accurately determined amount of metal particles such that
the metal is always smaller than the diamond particle sizes. The
methods may involve suspending the diamond particles in a liquid
and nucleating and growing precursor compound(s) for the required
metals on the surfaces of the diamond particles. The precursor
compound(s) is/are then conveniently converted to pure metals
attached to the diamond surfaces by heat treatment in reducing
furnace environment. Details of this method are set out in the
examples below. The homogeneity obtainable in the resulting PCD
material by such methods may be demonstrated and measured at a
scale greater than ten times the average diamond grain size. A
further constraint on the diamond grain size distribution in the
context of such homogeneous materials is that the maximum grain
size is preferably less than around three times the average diamond
grain size. Such homogeneous PCD materials may have improved
utility if they at least encompass the functional working volume.
Homogeneity in this regard may allow the avoidance of local stress
inducing inhomogeneity-based defect structures to occur. In turn
this may allow for the full exploitation of the residual stress
minimizing aspects as described above. Thus, for roller cone bit
applications, the PCD material of some examples material at least
encompass the functional working volume, and is homogeneous in that
it is spatially constant and invariant with respect to diamond
network and metallic network volume ratio, wherein the homogeneity
is measured at a scale greater than ten times the average grain
size, the maximum diamond grain size being less than around three
times the average diamond grain size.
[0097] In general roller cone bit applications for subterranean
rock drilling, the rock removal elements operate primarily by
crushing rock as indicated in FIG. 4. FIG. 4 shows a generally
example of a rock removal element utilizing a conventional prior
art thin layer (about 1 mm) of PCD material extending from an apex.
Although in such prior art constructions a benefit can accrue from
the very high wear resistance of PCD materials over cemented hard
metals, serious potentially life limiting delamination, and
chipping and spalling, of the PCD layer often occurs. The source of
such macroscopic crack phenomena may be primarily associated with
high magnitude tensile residual stress distributions in the PCD
material thin layers and in the cemented hard metal substrate
closely associated with the bonding interface between the PCD
material and the cemented hard metal. In the language of the
present disclosure, the residual stress distribution in the
functional working volume extending from the apex of the rock
removal element is of primary consideration and must be managed to
mitigate macroscopic crack behaviour such as chipping and spalling.
The methods of forming one or more examples which allow large
volumes of PCD material to be made bonded to hard metal substrates
may be of great benefit in this regard.
[0098] The example shown in FIG. 8c is an illustration of this,
whereby the generally convex curved surface of the PCD material
volume is hemispherical.
[0099] FIGS. 10a to d are a series of examples based upon FIG. 8c
where the residual stress distribution in the PCD material volumes,
and the cemented hard metal substrates are presented, resulting
from of a Finite Element Analysis (FEA). Such FEA techniques are
well established in the art and provide semi-quantitative and
qualitative information indicating compressive and tensile stress
fields, the positions of stress maxima and meaningful comparisons
of stress gradients in the stress fields. The examples of FIGS. 10a
to d are for bodies with cylindrical diameter of 16 mm and overall
length from the apices along the axis to the base of 27 mm. These
dimensions were chosen as examples for use in conventional roller
cone bit designs and custom and practice. The conclusions drawn
from the FEA analysis for the examples of FIGS. 10a-d are believed
to be applicable, for example, to the variations of dimensions and
shape of the examples indicated in FIGS. 8a-c and 9a&b.
[0100] In particular, FIGS. 10a, 10b, 10c and 10d are axial
cross-sections of rock removal body examples showing the zones of
principal residual stress magnitude, distinguished by grey shading.
The boundaries between the different shaded zones may be
interpreted as equi-stress contour lines. The thickness of the PCD
material layer expressed as the distance from the apices 1001 along
the axes to the interface of the PCD material to the boundary layer
on the axes 1002, are 2, 8, 10 and 16 mm for FIGS. 10a, 10b, 10c
and 10d, respectively. The line 1003 represents the thin
interfacial bonding barrier material separating the PCD material
volume above the line from the cemented hard metal substrate below
the line. This interfacial bonding barrier material is represented
by a single line, 1003, in these diagrams due to being very thin;
the boundary layer material does not significantly alter the
residual stress information presented. The zones or volumes of
overall compression are indicated by cross-hatching. Outside these
indicated compressive zones various levels of principal tensile
stress are indicated by different shades of grey. In the cemented
hard metal substrate in the direction along the axis towards the
interfacial bonding barrier layer 1003, the tensile stress
magnitude increases with the tensile stress maximum being just
below the interfacial line 1003 and indicated by the position 1004.
The functional working volumes in these embodiments are considered
to be invariant, of constant thickness, extending from the apices
1001 to the dotted line 1005.
[0101] In FIG. 10a, the interfacial bonding barrier line 1003 and
the boundary of the functional working volume, 1005, coincide. In
this case, the functional working volume and the PCD material
volume are one and the same. For the purposes of this example, the
thickness of the functional working volume, from 1001 along the
axis to the dotted line 1005, has been chosen to be 2 mm. In the
experience of the inventors, the most critical tensile residual
stress aspects are the high tensile maxima at or close to the free
surface of rock removal bodies. In the examples represented by
FIGS. 10a-d, these are indicated by 1004 and 1006, respectively.
1006 represents a tensile maximum in the PCD material volume above
the boundary line 1003 at or close to the free surface of the PCD
material volume. The tensile stress maximum 1006 in the PCD
material volume is dominated by an axial tensile stress. In the
case of FIG. 10a, the maximum stress 1006 has an axial and a radial
component. The tensile stress maximum 1004 immediately below the
interfacial boundary 1003 in the cemented hard metal substrate is
dominated by a combination of hoop radial tensile stresses.
[0102] In FIGS. 10a, 10b, 10c and 10d, the position where the
convex curved surface of the rock removal body joins with the
cylindrical barrel surface is indicated by 1007, which may be
described as the shoulder of the body. The shoulder may be further
described and defined as being the line of departure of the barrel
cylindrical surface extending into the generally convex curved
surface.
[0103] In FIG. 10b, the shoulder position 1007 coincides with the
intersection of the interfacial boundary line 1003 with the free
surface of the body. Note that, as FIGS. 10a, 10b, 10c and 10d are
considered as a progression of increased thickness and volume of
the PCD material volume, both the critical tensile stress positions
1004 and 1006 rapidly move away from the position of the invariant
functional working volume. As these critical points move away from
the functional working volume the probability of delamination,
chipping and spalling progressively becomes reduced. In particular,
when the critical stress position 1006 occurs below the shoulder
1007, both critical stress positions 1004 and 1006, may be
considered to be sufficiently remote from the invariant functional
working volume that the probability of delamination, chipping and
spalling of the functional volume becomes insignificant.
[0104] In some examples with generally convex curved surfaces for
the PCD material volume, where they take up hemispheroidal form,
these examples have the interfacial bonding material separating the
PCD material volume and the cemented hard metal substrate
intersecting the free surface of the body in the cylindrical barrel
surface below the shoulder, this being defined as the line of
departure of the barrel cylindrical surface extending into the
generally curve surface of the PCD material volume. The
hemispheroidal form of the generally convex curved surface of the
PCD material volume may be prolate hemispheroidal, oblate
hemispheroidal or hemispherical, as depicted in FIGS. 8a, 8b and
8c, respectively.
[0105] FIGS. 10c and 10d show the principal residual stress
distribution where the interfacial bonding material layer, 1003,
intersects the free surface of the body at the cylindrical barrel
surface below the shoulder, 1007. The PCD material thickness, from
the apex, 1001, along the axis 1002, i.e., to the interfacial
bonding line, 1003, increases from 10 mm to 16 mm for FIG. 10c to
FIG. 10d, respectively. Note that the positions of the critical
high tensile stress maxima 1004 and 1006, now progressively move to
positions even further remote from the functional working volume,
i.e., the volume of PCD between the dotted line 1005 and the apex
1001. This is considered to be progressively more and more
advantageous. Moreover, note that the tensile residual stress in
the functional working volume becomes progressively lower from FIG.
10c to FIG. 10d. Also note that at FIG. 10d the tensile residual
stress in the functional working volume approaches zero. In
addition, the gradient of tensile stress across the functional
working volume for this range of examples may be very low, for
example less than around 10 MPa/mm, which may be considered to be
negligible.
[0106] In applications where these examples will bear on the rock
surface with applied load very close to the axial direction, these
low tensile stresses in the functional working volume immediately
adjacent to the apex may be largely cancelled out by the applied
load. Clearly, in progressively moving from the example of FIG. 10c
to the example represented by FIG. 10d, the volume of PCD material
changes from being less than the volume of the hard metal substrate
to being greater than the volume of the hard metal substrate. The
examples represented by FIG. 10d may have a more favourable general
residual stress distribution for some applications, such as for
rock removal bodies intended for roller cone bit applications, as
the volume of the PCD material volume is greater than the cemented
hard metal substrate. As stated previously, however, all the
examples described preferably have sufficient surface area of hard
metal substrate to enable sufficient engagement and bonding to the
roller bit housing bodies or conical rollers. Creating the length
of the cylindrical hard metal substrate to be greater than the
radius of the cylindrical cemented hard metal substrate may assist
in achieving this. In addition, where the PCD material volume is
greater in volume than the cemented hard metal substrate, the
increased volume of PCD material adds strength to the overall body
by virtue of increased massive support to the apex bearing on the
rock strata.
[0107] Such examples may be expected to have lowered probabilities
of chipping, spelling and delamination. Moreover, since residual
stress related premature failure phenomena in and close to the
functional working volume are relegated to secondary
considerations, such examples may allow the exploitation of the
exceptional properties of PCD materials (with average diamond grain
sizes in the range 1 to 30 micro meters) in regard to the loading
situation typical of the roller cone bit applications, where the
rock is predominantly removed by a crushing action. These
properties are predominantly a combination of the high stiffness of
PCD materials exhibited by property measurements such as modulus of
elasticity at about a 1000 GPa, transverse rupture strength greater
than 1200 MPa and adequate impact resistance exhibited by fracture
toughness measurements (K.sub.lc) at about 9.5 MPa.m.sup.0.5. Such
measurements may be made with the techniques well established in
the art and technical literature. The PCD material in the examples
intended for roller cone bit applications thus may have an average
grain size in the range 1 to 30 micro meters, be homogeneous with
well intergrown diamond structure such the transverse rupture
strength is greater than 1200 MPa as measured in three point bend
tests. In this broad range of PCD materials, in this particular
application PCD materials with the highest compressive strength may
be favoured. This implies PCD material types with higher diamond
content, with good intergrowth. Typically, these would be materials
with larger average grain sizes, such as in the range 10 to 30
micro meters.
[0108] As described above, one or more of the examples, be they
intended for drag bit or roller cone bit applications, may have a
refractory metal diffusion blocking barrier of material may assist
in preventing the molten cementing metal of the hard metal
substrate and the molten catalyst/solvent metal of the PCD material
volume from interacting with one another during the manufacturing
process at high pressure high temperature. In addition, such
materials may also provide bonding between the PCD material volume
and the cemented hard metal substrate. Typical materials which can
serve such purposes, may be, for example, thin (eg around 20 to
around 100 micro meters thickness) refractory metal layers chosen,
for example, from any combination of one or more of tantalum,
vanadium, molybdenum, zirconium, tungsten and alloys thereof.
During the high temperature high pressure manufacturing process,
these layers of refractory metals may be chosen such that they do
not melt but will be subject to exposure to high carbon content
molten transition metals such as molten cobalt-carbon alloy. Thus,
these transition metals become partially carburised during the
process.
[0109] Also, certain thin ceramic layers deposited using PVD or CVD
techniques may also assist in providing a barrier, bonding layer
for one or more of the examples. The refractory bonding interfacial
layer separating the PCD material volume and the cemented hard
metal substrate may be, for example, a CVD or PVD deposited
continuous ceramic layer of greater than, for example, around 3
micro meters thickness, chosen for example, from any combination of
nitrides of the elements of Group IVa, Va or VIa of the periodic
table, such as titanium nitride, TiN.
[0110] Some of the examples, be they intended for drag bit or
roller cone bit applications, may enjoy the benefits of the tensile
residual stress distribution in and around the functional working
volume being radically reduced in magnitude and intensity of
gradient. Moreover, the principal tensile residual stress maxima
may be significantly removed from and remote from the functional
working volume and its environs. This may provide for a beneficial,
significantly lowered possibility or probability of chipping and
spelling in and close to the functional working volume. The common
feature which may assist in providing this is if the PCD material
volumes are large and are comparable in volume to the cemented hard
metal substrate or indeed are greater in volume than the cemented
hard metal substrate. The latter being the case for rock removal
bodies intended for roller cone bit applications. For rock removal
bodies intended for drag bit applications, which may be restricted
to an overall right cylindrical shape, the desired size of the PCD
material volume is expressed by stipulating that the PCD material
volume thickness is around 3 mm or greater. The examples of FIGS.
7a-c and 10a-d where the residual stress distributions are
presented, are used to illustrate the reduction of tensile stress
in the functional working volume as the magnitude of the volume of
the PCD material volume increases. However, it may be observed in
FIGS. 7a to 10d, that although tensile stress maxima may be made to
be remote from the functional working volumes by appropriately
large PCD material volume, they may remain as aspects of concern,
in that these maxima may contribute to the possibility of impact
related failure during application such as splitting and
delamination of the cemented hard metal substrate. These tensile
stress maxima are illustrated in FIGS. 7b and 7c for examples
intended for drag bit applications. They are the axial tensile
maximum in the PCD material volume positioned between the dotted
line 709 and the cylindrical free surface, forming a ring of highly
tensed material and the combined radial and hoop tensile maximum in
the cemented hard metal substrate positioned between the dotted
line 707 and the line representing the interfacial barrier, 701,
which separate the PCD material volume and the cemented hard metal
substrate.
[0111] Similarly, the tensile stress maxima are illustrated in
FIGS. 10c and 10d for examples intended for roller cone bit
applications. They are the axial tensile stress maxima in the PCD
material volume 1006 and the combined hoop and radial tensile
maxima, 1004, in the cemented hard metal substrate. It may be
advantageous if the magnitude of these tensile stress maxima were
to be reduced. A general way of doing this may be to minimize the
difference between the average coefficient of thermal expansion of
the PCD material volume and that of the cemented hard metal
substrate. This may be done by choosing the PCD material to have a
relatively high linear coefficient of thermal expansion in the
typical range of PCD materials (around 3.7 to around 4.4 ppm.
.degree. K.sup.-1) in conjunction choosing the cemented hard metal
material to have a relatively low linear coefficient of thermal
expansion in the range typical of cemented hard metal materials
typically used in subterranean rock drilling applications (around
5.0 to around 6.1 ppm. .degree. K.sup.-1), for example.
[0112] In PCD materials made with cobalt as the catalyst solvent
metal, the high linear coefficient of thermal expansion at the top
of the range may restrict the PCD material to having a high metal
cobalt content of at least above 9 volume percent. The cemented
hard metal grades typically used in subterranean rock drilling
applications are cobalt cemented tungsten carbide grades chosen
within the range of 6 to 14 weight percent cobalt. Cemented hard
metal carbide with low coefficient of thermal expansion may be
restricted to grades with low cementing metal contents at most 10
weight percent (16.3 volume percent) cobalt.
[0113] Examples which exhibit lowered tensile stress maxima may be
used where the metallic network of the PCD material is, for
example, a cobalt-carbon alloy and the cementing metal of the hard
metal substrate is, for example, a cobalt-tungsten-carbon alloy and
the average metal content of the PCD material volume is, for
example, greater than around 9 volume percent (20 weight percent)
together with the average cobalt content of the hard metal
substrate being less than around 16.3 volume per cent (10 weight
percent).
[0114] Some of the examples employ PCD material volumes where the
composition and structure of the PCD material is macroscopically
invariant and homogeneous across the dimensional extent of the PCD
material volume. The composition and structure of the cemented hard
metal substrates may also be invariant across the dimensional
extent of the substrate, i.e., made of one grade of cemented hard
metal for these examples. Residual stress distributions extending
across the macroscopic dimensions of high pressure high temperature
PCD material bodies may be altered, manipulated and chosen by
grading the composition of PCD material across the dimensions of
the bodies. This may be done by graduating and changing the metal
composition as a function of position in the PCD material volume
such that the linear coefficient of thermal expansion is different
as a function of position in the PCD material volume. The
differential shrinkage of the PCD material from position to
position during the cooling and pressure reduction phase of high
pressure high temperature manufacturing process then induces
residual stress from position to position. This method may be used
by such positional choice of PCD material composition and structure
to assist in reducing the intensity of tensile stress maxima and
thus render them less likely to cause undesirable crack related
fracture events such as chipping, spelling and delamination. This
may be done by altering the composition and structure in a
graduated way across the dimensions of the PCD material volume
and/or by using discrete adjacent volumes of PCD materials
differing appropriately in composition and linear coefficient of
thermal expansion.
[0115] This approach to manipulation and control of the residual
stress distribution may also be applied to the cemented hard metal
substrate. Similarly, different grades of cemented hard metal
materials with differing linear coefficients of thermal expansion
may be employed in various positions in the substrate to
advantageously lower tensile residual stress. These teachings may
be applied to the examples so far disclosed herein. To illustrate
this, FIGS. 11a and 11b are cross-sectional diagrams representing
the arrived at examples for drag bit and roller cone bit
applications, respectively. The PCD material volumes and cemented
hard metal substrate are labelled 1101 and 1102, respectively. The
interfacial barrier layer material is represented by the line 1103.
In FIG. 11a representing examples for drag bit applications, the
functional working volume is the volume between a point on the
circumferential edge, 1104, and the dotted line 1105. The point
1104 represents the initial part of the functional working volume
to be made to bear on the rock during rock drilling applications.
In FIG. 11b representing the examples for roller cone bit
applications the functional working volume is represented by the
volume of PCD material between the apex 1106 and the dotted line
1105. The apex 1106 represents the initial part of the functional
working volume to bear on the rock during drilling
applications.
[0116] In both FIGS. 11a and 11b the central axial lines of the
bodies intersect the free surface of the PCD material volume and
the cemented hard metal substrate at 1106 and 1112, respectively.
For FIG. 11b, the apex 1106 is also the apex of the generally
convex curved surface of the PCD material volume. In both FIGS. 11a
and 11b, the position of the axial dominated principal tensile
residual stress maximum in the PCD material volume is indicated by
1107. Note that this tensile stress maximum is just above the
interfacial boundary layer 1103 at or close to the cylindrical free
surface of the PCD material volume. This tensile stress maximum
thus forms an extended circumferential position. In FIGS. 11a and
11b, the positions of the combined radial and hoop dominated
principal tensile residual stress maximum in the cemented hard
metal substrate is indicated by 1108. Note that this tensile stress
maximum is positioned just below the interfacial barrier layer 1103
and this general high tensile stress extends along the interface
1103, such that it diminishes in the direction of the intersection
of the interface 1103 and the axes of the bodies.
[0117] As described above, during the reduction of pressure and
temperature at the end of the high pressure high temperature
manufacturing process both the PCD material volume and the cemented
hard metal substrate shrink. The shrinkage of typical PCD material
volumes is always less than that of the cemented carbide material
volume. This is because the linear coefficient of thermal expansion
of typical PCD materials is always less than that of cemented hard
metal materials. The arrows 1109 and 1110 in FIGS. 11a and 11b
represent the radial shrinkage of the PCD material volume and the
cemented hard metal substrate, respectively, on either side of the
interfacial barrier layer 1103 in an example PCD material. Note
that the arrow 1109 is shorter than the arrow 1110, the difference
in arrow length indicating the differential shrinkage. The net
result of this differential shrinkage are bending effects which
give rise to the residual stress distributions in both the PCD
material volume and the cemented hard metal substrate. The axial
direction dominated residual stress maximum in the PCD material
volume, 1107, and the radial and hoop direction dominated residual
stress maximum in the cemented hard metal substrate, 1108,
therefore result from the difference in shrinkage. If the material
of the PCD material volume is altered as a function of position
such that the linear coefficient of thermal expansion increases in
the general direction away from 1104 in FIG. 11a and 1106 in FIG.
11b in the general direction of the interfacial barrier 1103, the
differential shrinkage and bending effects may be reduced,
resulting in the magnitude of 1107 and 1108 stress maxima being
reduced. This general direction is represented by the arrows 1111
which extend from the points of first contact with the rock during
rock drilling applications, 1104 and 1106, towards the interfacial
barrier layer 1103.
[0118] Examples where the linear coefficient of thermal expansion
of the PCD material increases in the general direction away from a
point which is part of the functional working volume which
initially bears upon the rock in use, towards the interfacial
barrier layer separating the PCD material volume and the cemented
hard metal substrate may be advantageous due to the reduction of
the residual stress maxima. The value of the linear coefficient of
thermal expansion of the PCD material at any given position in the
PCD material volume is determined by the elemental composition and
quantity of the metal component of the PCD material at and close to
that given position. Where the metal type or alloy is invariant
across the dimension of the PCD material volume, the linear
coefficient of thermal expansion is varied by the metal content
alone. The higher metal contents correspond to PCD materials of the
highest coefficient of thermal expansion. The converse is also
true.
[0119] Examples where the metal of the PCD material is invariant as
regards the metal type or alloy across the dimensions of the PCD
material volume and where the metallic content of the PCD material
increases in the general direction away from a point which is part
of the functional working volume which initially bears upon the
rock in use, towards the interfacial barrier layer separating the
PCD material volume and the cemented hard metal substrate may be
advantageous due to the reduction of the magnitude of the residual
stress maxima. A convenient way of generally increasing the linear
coefficient of thermal expansion across a macroscopic dimension in
a particular direction may be to employ discrete adjacent volumes
of PCD materials differing in linear coefficient of thermal
expansion and metal content. The differential shrinkage of the
appropriately differing PCD material adjacent volumes may thus
provide for a reduction in the overall shrinkage of the overall PCD
material volume. Thus, one or more examples may comprise a PCD
material volume comprising two or more layers of differing PCD
material, the first layer of lowest linear coefficient of thermal
expansion and metal content extends from the free surface and
encompasses the functional working volume, with the second or
subsequent layers of higher linear coefficient of thermal expansion
and metal content separating the first layer from the interfacial
barrier which separates the PCD material volume and the cemented
hard metal substrate. Such examples using simple layers of
differing PCD material may be very conveniently made and may
significantly reduce the magnitude of critical residual stress
tensile maxima. An example which demonstrates this is shown in FIG.
12.
[0120] FIG. 12 is a half cross-section of an example intended for
drag drill bit applications, which is a rock removal body of
overall right cylindrical shape, is 16 mm in diameter, 16 mm in
overall length, with a PCD material volume of 6 mm thickness and
cemented hard metal substrate of close to 10 mm long. This overall
shape, and the dimensions and thickness of PCD material volume
correspond to the example presented in FIG. 7b.
[0121] FIG. 12 shows the form of the residual stress distribution
in the example as derived from Finite Element Analysis (FEA). In
FIG. 12, the PCD material volume, 1201, comprises a first layer of
PCD material, 1202, of 3.5 mm thickness, with linear coefficient of
thermal expansion less than a second layer of PCD material, 1203,
of thickness 2.5 mm which separates the first PCD material layer
from the interfacial barrier layer represented by the line 1204.
The catalyst/solvent metal forming the metallic network in the PCD
material volume 1201 was cobalt. The first layer of PCD material,
1202, had a cobalt content of 6.7 volume percent and the second
layer of PCD material had a cobalt content of 11.5 volume percent.
The cemented hard metal substrate 1205 was chosen to comprise a
tungsten carbide cobalt cemented hard metal with a cobalt content
of 13 weight percent and a linear coefficient of thermal expansion
of 5.6 ppm. .degree. K.sup.-1. The principal residual stress
distribution is presented in FIG. 12 by a series of grey shaded
volumes which are delineated and separated by contour lines of
equal stress. The zero stress contour lines, separating regions of
tensile and compressive residual stress are indicated by dotted
lines with the volumes under residual compression being
cross-hatched. Note that the principal residual stress in the
functional working volume is low.
[0122] The functional working volume is indicated as the volume of
material between the specific point 1206 and the dotted line 1207.
1206 is the specific point on the circumferential edge of the PCD
volume which is chosen to initially bear on the rock during the
application. The functional working volume extends down the
circumferential free surface by a chosen 3 mm. The principal
tensile residual stress maximum, 1208, is at a position on the
circumferential free surface of the PCD material volume immediately
above the interfacial barrier layer 1204, forming a ring around the
circumference in the second PCD material layer 1203. This residual
stress maximum, 1208, is dominated by an axial tensile stress and
corresponds in position to the maximum tensile residual stress
indicated in FIG. 11a, 1107, and FIG. 7b, 709. Note that the
principal residual stress in the cemented hard metal substrate at
the base and circumferential free surface is low, ostensibly
neutral. In the general direction from the base towards the
interfacial barrier layer 1204, the tensile residual stress
progressively increases in magnitude and reaches a maximum
immediately below the interfacial barrier layer 1204. The position
of this maximum principal tensile residual stress is indicated by
1209. The maximum residual tensile stress 1209 corresponds to the
tensile stress maximum in FIG. 11a, 1108, and the indicated maximum
in FIG. 7b, 707. This tensile residual stress maximum is dominated
by radial and hoop tensile stress components at this position in
the cemented hard metal substrate.
[0123] When the magnitude of the tensile stress maxima in FIG. 7b,
709 and 707, are compared with the magnitude of the corresponding
tensile stress maxima in FIG. 12, 1208 and 1209, using the ABAQUS
finite element analysis program well known in the art, it was found
that both maxima had been reduced by around 10%. This reduction for
the example of FIG. 12 may be considered to be significant and
favourable. In the example represented by FIG. 12, where the PCD
material volume comprises two or more layers of differing PCD
material, the first layer of lowest linear coefficient of thermal
expansion and metal content extends from the free surface and
encompasses the functional working volume, with the second or
subsequent layers of higher linear coefficient of thermal expansion
and metal content separating the first layer from the interfacial
barrier which separates the PCD material volume and the cemented
hard metal substrate. Such examples may be valuable for some
applications as these critical stress maxima may be significantly
reduced in magnitude. This reduction may provide for a beneficial
reduced tendency for the cemented hard metal substrates of these
examples to delaminate and split during rock drilling
applications.
[0124] As discussed above, graduating the properties of the
cemented hard metal substrate may also be employed to reduce the
differential shrinkage indicated by the arrows 1109 and 1110 in
FIGS. 11a and 11b. A reduction in the differential shrinkage may
give rise to lowering the bending effect which occurs at the end of
the high pressure high temperature manufacturing process which may
result in a beneficial reduction of the magnitude of the tensile
stress maxima already described and indicated by 1107 and 1108. If
the composition and resultant properties of the cemented hard
material are altered such that the linear coefficient of thermal
expansion decreases in the general direction from the central point
of the base of the substrate 1112, towards the interfacial barrier
layer 1103, indicated by the arrows 1113, such a reduction of the
magnitude of the tensile residual stress maxima may occur. Thus,
some of the examples may have a linear coefficient of thermal
expansion of the cemented hard metal substrate decreasing in the
general direction away from the central point of the base of the
body towards the interfacial barrier layer separating the PCD
material volume and the cemented hard metal substrate. If the
cemented hard metal substrate is made of one type of hard metal
material such that the cementing metal and the hard compound are
invariant as regards metal type and molecular composition, then the
amount of cementing metal may decrease in the general direction
away from the central point of the base of the body towards the
interfacial barrier layer separating the PCD material volume and
the cemented hard metal substrate.
[0125] A convenient way of generally decreasing the linear
coefficient of thermal expansion of the cemented hard metal
substrate across a macroscopic dimension in a chosen general
direction may be to employ discrete adjacent volumes of cemented
hard metal materials differing in linear coefficient of thermal
expansion and cementing metal content. A set of examples in this
regard may use parallel layers of differing hard metal material of
varying thickness. In some examples, where, for example, the
cemented hard metal substrate comprises two or more layers of
differing hard metal material, the first layer of highest linear
coefficient of thermal expansion and metal content may extend from
the basal free surface of the substrate, with the second or
subsequent layers of lower linear coefficient of thermal expansion
and metal content separating the first layer from the interfacial
barrier which separates the PCD material volume and the cemented
hard metal substrate.
[0126] FIG. 13 is an example based upon the shape and dimensions of
the example represented by FIG. 7b, which illustrates the potential
benefits of employing such appropriately arranged discrete layers
of differing cemented hard metal carbide materials. In FIG. 13, the
PCD material volume 1301 may comprise, for example, a homogeneous
PCD material with a linear coefficient of thermal expansion of
around 4.0 ppm. .degree. K-1 and a cobalt content of around 9
volume percent (around 20 weight percent). The cemented hard metal
substrate, 1302, comprises two layers of differing material 1303
and 1304. The boundary between these layers is substantially planar
and parallel to the base of the substrate. In some examples, the
layer 1303 extending from the base of the substrate may be around 8
mm thick and made of a tungsten carbide cobalt hard metal with
around 14 weight percent cobalt (around 22.2 volume percent) and
may have a linear coefficient of thermal expansion of around 6.01
ppm.oK-1. The layer 1304, which separates the layer 1303 from the
interfacial barrier layer 1305 may be around 2 mm thick and may
comprise a tungsten carbide cobalt hard metal with around 6 weight
percent (10.1 volume percent) cobalt and a linear coefficient of
thermal expansion of around 5.09 ppm.oK-1. The principal residual
stress distributions in this example are presented as zones of
varying shades of grey as before, with the same general qualitative
character as exhibited in FIGS. 7b and 12.
[0127] The positions of the axial dominated tensile principal
residual stress maximum, 1306, in the PCD material volume, 1301,
corresponds to 709 in FIG. 7b, 1107 in FIG. 11a and 1208 in FIG.
12. The position of the radial and hoop component dominated tensile
principal stress maximum, 1307, in the hard metal substrate 1302
corresponds to 707 in FIG. 7b and 1108 in FIG. 11a and 1208 in FIG.
12. Finite element analysis carried out on this example
demonstrated that the magnitude of both the critical tensile stress
maxima, 1306 and 1307, is reduced by around 35 percent as compared
to the corresponding maxima 709 and 707 in FIG. 7b. Thus, this
example may be considered to show a significant reduction in the
magnitude of these critical tensile stress magnitudes. This may be
highly beneficial, leading to a significantly reduced risk and
probability of delamination and splitting of the cemented hard
metal substrate during rock drilling applications.
[0128] The examples of FIG. 12 and FIG. 13 may be combined to form
yet another example which is shown in FIG. 14. The two layered
arrangement of differing PCD materials of FIG. 12 are combined with
the two layer arrangement of differing tungsten carbide cobalt hard
metal of FIG. 13. Finite element analysis of this example shows
that the magnitude of the tensile principal stress maxima, 1401 and
1402, corresponding to the critical stress maxima, 709 and 707 in
FIG. 7b, and 1107 and 1108 in FIG. 11a, may reduced by around 60
percent. This may, in some applications, be considered to be a
highly desirable and beneficial situation of significantly reduced
critical residual stress distributions, leading to an expectation
that delamination and splitting of the hard metal substrate during
drilling operations may become unlikely. This example illustrates
the potential value in combining the grading of the PCD material
volume in composition and structure such that the linear
coefficient of thermal expansion of the PCD material increases in
the general direction away from a point which is part of the
functional working volume which initially bears upon the rock in
use, towards the interfacial barrier layer separating the PCD
material volume and the cemented hard metal substrate, with the
decreasing of the linear coefficient of thermal expansion of the
hard metal substrate in the general direction away from the central
point of the base of the body towards the interfacial barrier layer
separating the PCD material volume and the cemented hard metal
substrate.
[0129] In some examples, the metal network in the PCD material
volume is cobalt and the cemented hard metal substrate is tungsten
carbide cobalt.
[0130] The examples for drag bit applications shown in FIGS. 12, 13
and 14 may be generally applicable, and include the examples
intended for use in roller cone applications whereby the rock
removal body comprises a right circular cylinder with one end
forming a generally convex curved surface with an apex. The PCD
material volumes in such examples may extend from the apices and
the curved free surface.
[0131] Most of the examples so far described above exhibit a flat
planar thin interfacial barrier layer derived from a refractory
material which acts as a metal diffusion blocking barrier to the
molten bonding material of the hard metal substrate and the molten
catalyst solvent sintering aid of the polycrystalline material
during the high pressure high temperature manufacturing process.
However, the residual stress distribution in the PCD material
volume of general composite PCD hard metal substrate bodies may be
favourably altered by employing a non-flat, non-planar interface or
boundary between the PCD material volume and the hard metal
substrate. More explicitly, such non-planar interfaces or
boundaries may have improved value in reducing tensile residual
stress maxima, for example if they exhibit a general arcuitly
convex curvature towards the PCD material volume.
EXAMPLES
[0132] Some further examples are now described in more detail and
are not intended to be limiting.
Example 1
[0133] Rock removal bodies intended for subterranean rock drilling
using drag bit designs and technology were made corresponding to
the embodiment illustrated in FIG. 14. This example was a
combination of the two cylindrical layer PCD material volume of
FIG. 12 and the two cylindrical layer cemented hard metal substrate
of FIG. 13.
[0134] The bodies each comprised a right circular cylinder of 16 mm
diameter and overall length 16 mm with one end forming a
cylindrical PCD material volume of thickness 6 mm, with a cemented
hard metal substrate disposed at the opposite cylindrical end of
the body. The PCD material volume of each body was comprised of a
first cylindrical layer, 1202, of 3.5 mm thickness extending from
the flat top circular free surface of the body and a second layer,
1203, of 2.5 mm thickness separating the first PCD layer from an
extant barrier boundary layer and the cemented hard metal
substrate. It is intended that the first layer will completely
encompass the functional working volume in use, which extends about
3 mm down the barrel free surface of the PCD material volume from a
chosen point at a circumferential edge of the body, this point
being the point of initial contact with the rock strata.
[0135] This first layer was made from a multimodal PCD material
with an average grain size of close to 10 micro meters, with the
grain size distribution extending from about 1 to 30 micro meters.
The term multimodal in this context refers to the starting diamond
powder, which was produced by combining five separate powers,
differing in average particle size distribution. The first layer
was made from five component diamond powders having a single
maximum in particle size distribution and hence each component
being monomodal. The metal employed as catalyst solvent for partial
re-crystallization of the diamond was cobalt, resulting in the
interpenetrating network of the resultant PCD material being high
carbon containing cobalt. The PCD material had a cobalt content of
6.7% by volume (15.4% by weight). This composition of PCD material
is known to have a linear coefficient of thermal expansion of 3.7
ppm .degree. K.sup.-1.
[0136] This second layer was made from a multimodal PCD material
with an average grain size of close to 6 micro meters, with the
grain size distribution extending from about 1 to 20 micro meters.
This layer was made from three component diamond powders having a
single maximum in particle size distribution and hence each
component being monomodal. The metal employed as catalyst solvent
for partial re-crystallization of the diamond was cobalt, resulting
in the interpenetrating metallic network of the resultant PCD
material being high carbon containing cobalt. The PCD material had
a cobalt content of 11.5% by volume (24.7% by weight). This
composition of PCD material is known to have a linear coefficient
of thermal expansion of 4.4 ppm .degree. K.sup.-1.
[0137] The two layer hard metal substrate was made from tungsten
carbide cemented with cobalt. The layer at the base of the
substrate, 1303 in FIG. 14, was 8 mm long with 14 weight % (22.2
volume %) cobalt content. This grade of hard metal had a linear
coefficient of thermal expansion of 6.01 ppm .degree. K.sup.-1. The
layer separating this layer from the thin barrier layer material
and the PCD material volume, 1304 in FIG. 14, was 2 mm thick, with
a 6 weight % (10.1 volume %) cobalt content. This grade of hard
metal had a linear coefficient of thermal expansion of 5.09 ppm
.degree. K.sub.-1.
[0138] Note that for these bodies the linear coefficient of thermal
expansion of the PCD material increased in the general direction
away from a point which is part of the functional working volume
which initially bears upon the rock in use, towards the interfacial
barrier layer separating the PCD material volume and the cemented
hard metal substrate, with the linear coefficient of thermal
expansion of the hard metal substrate decreasing in the general
direction away from the central point of the base of the body
towards the interfacial barrier layer separating the PCD material
volume and the cemented hard metal substrate.
[0139] Precursor compounds for the metal, in this case cobalt, are
precipitated, nucleated and grown on the surface of the diamond
particles by using reactions between soluble reactants whilst
suspending the diamond powder in water. After removal from
suspension, drying and subsequent heat treatment in reducing
environments the diamond particle surfaces are decorated in pure
metal particles, thus ensuring an extremely high degree of
homogeneity of mixing with respect to the diamond and metal
components.
[0140] The stock mass for the material of the first PCD layer was
produced using the following procedural steps.
[0141] 100 g of diamond powder was suspended in 2.5 litres of
de-ionised water. The diamond powder comprised 5 separate monomodal
diamond fractions each differing in average particle size. The
diamond powder was thus considered to be multimodal. The 100 g of
diamond powder was made up as follows: 5 g of average particle size
1.8 micro meters, 16 g of average particle size 3.5 micro meters, 7
g of average particle size 5 micro meters, 44 g of average particle
size 10 micro meters and 28 g of average particle size 20 micro
meters. This multimodal particle size distribution extended from
about 1 micro meter to about 30 micro meters.
[0142] The diamond powder had been rendered hydrophilic by prior
acid cleaning and washing in de-ionised water. To the suspension an
aqueous solution of cobalt nitrate and a separate aqueous solution
of sodium carbonate were simultaneously slowly added while the
suspension was vigorously stirred. The cobalt nitrate solution was
made by dissolving 93 g of cobalt nitrate hexahydrate crystals,
Co(NO.sub.3).sub.2.6H.sub.2O, in 200 ml of de-ionised water. The
sodium carbonate solution is made by dissolving 33.9 g of pure
anhydrous sodium carbonate, Na.sub.2CO.sub.3 in 200 ml of
de-ionised water. The cobalt nitrate and sodium carbonate reacted
in solution precipitating cobalt carbonate CoCO.sub.3, as per the
following equation,
##STR00001##
[0143] In the presence of the suspended diamond powder particles,
with their hydrophilic surface chemistry, the cobalt carbonate
crystals nucleated and grew on the diamond particle surfaces. The
cobalt carbonate precursor compound for cobalt, took the form of
whisker shaped crystals decorating the diamond particle surfaces.
The sodium nitrate product of reaction was removed by a few cycles
of decantation and washing in de-ionised water. The powder was
finally washed in pure ethyl alcohol, removed from the alcohol by
decantation and dried under vacuum at 60.degree. C.
[0144] The dried powder was then placed in an alumina ceramic boat
with a loose powder depth of about 5 mm and heated in a flowing
stream of argon gas containing 5% hydrogen. The top temperature of
the furnace was 750.degree. C. which was maintained for 2 hours
before cooling to room temperature. This furnace treatment
dissociated and reduced the cobalt carbonate precursor to form pure
cobalt particles, with some carbon in solid solution decorating the
surfaces of the diamond particles. In this way it was ensured that
the cobalt particles were always smaller than the diamond particles
with the cobalt being homogeneously distributed. The conditions of
the heat treatment were chosen with reference to the standard
cobalt carbon phase diagram of the literature. At 750.degree. C. it
may be seen that the solid solubility of carbon in cobalt is low.
At these conditions the formation of amorphous non-diamond carbon
at this temperature is low and traces of non-diamond carbon could
be detected in the final diamond-metal particulate mass. The
resultant powder mass of multimodal diamond particles with an
overall 15.4 weight % of cobalt metal decorating the diamond
particle surfaces had a pale light grey appearance. This powder
stock mass for the first PCD material layer was stored under dry
nitrogen in an air-tight container to prevent oxidation of the fine
cobalt decorating the diamond surfaces.
[0145] The stock mass for the material of the second PCD layer was
produced using the following procedural steps.
[0146] 100 g of diamond powder was suspended in 2.5 litres of
de-ionised water. The diamond powder comprised 3 separate monomodal
diamond fractions each differing in average particle size. The
diamond powder was thus considered to be multimodal. The 100 g of
diamond powder was made up as follows: 18 g of average particle
size 4 micro meters, 70 g of average particle size 6 micro meters
and 12 g of average particle size 12 micro meters. This multimodal
particle size distribution extended from about 1 micro meter to
about 20 micro meters.
[0147] The same sequential steps were then carried to precipitate a
cobalt carbonate precursor for the cobalt metal onto the surfaces
of the diamond particles as that for the stock mass for the first
PCD layer material save that the cobalt nitrate solution was made
by dissolving 160 g of cobalt nitrate hexahydrate crystals,
Co(NO.sub.3).sub.2.6H.sub.2O, in 200 ml of de-ionised water. The
sodium carbonate solution is made by dissolving 60 g of pure
anhydrous sodium carbonate, Na.sub.2CO.sub.3 in 200 ml of
de-ionised water. The resultant powder mass of multimodal diamond
particles with an overall 24.7 weight % of cobalt metal decorating
the diamond particle surfaces was stored under dry nitrogen in an
air-tight container to prevent oxidation of the fine cobalt
decorating the diamond surfaces.
[0148] For each rock removal body, so called green body assemblies
were constructed using thin walled tantalum canisters. The
qualitative and geometric arrangement of the green body assemblies
is schematically illustrated in FIG. 15, the drawing not being to
scale. 2.3 g of the stock particulate mass for the first PCD
material layer, 1501, was pre-compacted into a tantalum canister,
1503, in a uniaxial hard metal compaction die to form a semi-dense
right cylindrical layer at the bottom of the canister. This was
followed by pre-compacting 2.8 g of the stock particulate mass for
the second PCD material layer, 1502, into place into canister
1503.
[0149] A 2.0 mm thick tungsten carbide 6 weight % (10.1 volume %)
cobalt hard metal disc, 1504, was then inserted into the bottom of
a tantalum canister, 1506, followed by 8.5 mm thick tungsten
carbide 14 weight % (22.2 volume %) cobalt hard metal disc, 1505.
These two hard metal discs together formed the substrate. The
tantalum encompassed end of the substrate was then inserted into
the open end of the diamond mass containing canister, 1503, such
that the end wall of the canister, 1506, separated the diamond mass
from the substrate, and further uniaxial compacted to form the
assembly. After appropriate trimming of the open end of the
canisters, the assembly was inserted into a third canister of
slightly larger diameter, 1507, vacuum degassed and sealed under
vacuum using procedures known in the art. To consolidate further,
to a higher green density and to eliminate or radically reduce
spatial density variations, the canister assembly was then
subjected to a cold isostatic compaction procedure at a pressure of
200 MPa. Several so called green body assemblies were produced in
this manner.
[0150] Note that the end wall of canister, 1506, separates the
diamond particulate masses which will form the PCD material volume
and the hard metal substrate. This thin, about 50 micro meters
thick, tantalum end wall layer acted as a barrier to both the
molten cementing cobalt of the substrate and the molten cobalt of
the PCD material layer during sintering of the diamond PCD layer at
high pressure and temperature. In this way the metallic component
of the PCD material volume and the cementing metal of the hard
metal substrate were independent of one another, independently
derived and did not interacted during the high pressure high
temperature manufacturing process. After the high pressure
sintering of the PCD material volume an extant partially carburised
tantalum layer separated the PCD material volume from the
substrate.
[0151] To sinter the diamond particles of PCD material volume, by
partial re-crystallisation of the diamond, each green body assembly
was then placed in an assembly of compactable ceramic, salt
components suitable for high pressure high temperature treatment as
well established in the art. The material immediately surrounding
the encapsulated green body was made from very low shear strength
material such as sodium chloride. This provides for the green
bodies being subjected to pressures which approach a hydrostatic
condition. In this way pressure gradient induced distortions of the
green body may be mitigated.
[0152] The green body canister assemblies were then subjected to a
pressure of 6 GPa and a temperature of approximately 1560.degree.
C. for 1 hour using a belt type high pressure apparatus as well
established in the art. During the end phase of the high pressure
high temperature procedure the temperature was slowly reduced over
several minutes to approximately 750.degree. C., maintained at this
value and then the pressure was reduced to ambient conditions. The
high pressure assembly was then allowed to cool to ambient
conditions before extraction from the high pressure apparatus. This
procedure during the end phase of the high pressure high
temperature treatment was thought to allow the surrounding salt
media to remain in a plastic state during the removal of pressure
and so prevent or inhibit shear forces bearing upon the now
sintered PCD body.
[0153] The fully dense, right cylindrical bodies were then brought
to dimensions of 16 mm diameter and 16 mm long, by finishing
procedure such as fine diamond grinding and polishing as well
established in the art. Several samples of the embodiment
represented by FIG. 14, with two layers of differing PCD material,
and two layers of differing tungsten carbide/cobalt hard metal
substrate were in this way prepared, performed well in laboratory
rock removal testing and did not display significant chipping and
spelling behaviour.
Example 2
[0154] Rock removal bodies intended for subterranean rock drilling
using roller cone bit designs and technology were made
corresponding to the example illustrated in FIG. 10d. The bodies
each comprised a right circular cylinder with one end forming a
generally convex surface, specifically a hemisphere, with a PCD
material volume extending from the apex, 1001, of the hemisphere. A
hard metal substrate was disposed at the opposite cylindrical end
of the body. This substrate was made of a cobalt cemented tungsten
carbide hard metal, with 12.75 weight percent of cobalt. The PCD
material volume was separated from and bonded to the cemented
cylindrical hard metal substrate by a partially carburized tantalum
interfacial layer of 50 micro meters thickness, indicated by the
line 1003 in FIG. 10d. This layer acted as a barrier during
manufacture and prevented the molten cementing metal of the hard
metal substrate and the molten metal of the PCD material volume
interacting. The diameter of the cylindrical part of the bodies was
finished to be 16 mm. The overall length of each body was 27 mm as
measured from the apex, 1001, along the axis of the body to the
center of the circular base. The length of the PCD material volume
as measured from the apex, 1001, to the intersection of the axial
line, 1002, with the interfacial layer, 1003, was 16 mm. The length
of the tungsten carbide/cobalt substrate was close to 11 mm.
[0155] The PCD material volume was made of a multimodal PCD
material with an average grain size of close to 10 micro meters,
with the grain size distribution extending from about 1 to 30 micro
meters. The term multimodal in this context refers to the starting
diamond powder, which was produced by combining five separate
powers, differing in average particle size distribution. Each made
of five component diamond powders having a single maximum in
particle size distribution and hence being monomodal. The metal
employed as catalyst solvent for partial re-crystallization of the
diamond was cobalt, resulting in the interpenetrating network of
the resultant PCD material being high carbon containing cobalt. The
PCD material had a cobalt content of 9% by volume (20% by
mass).
[0156] Precursor compounds for the metal, in this case cobalt, are
precipitated, nucleated and grown on the surface of the diamond
particles by using reactions between soluble reactants whilst
suspending the diamond powder in water. After removal from
suspension, drying and subsequent heat treatment in reducing
environments the diamond particle surfaces are decorated in pure
metal particles, thus ensuring an extremely high degree of
homogeneity of mixing with respect to the diamond and metal
components.
[0157] The procedural sequential steps of the method for this
example are as follows.
[0158] 100 g of diamond powder was suspended in 2.5 litres of
de-ionised water. The diamond powder comprised 5 separate monomodal
diamond fractions each differing in average particle size. The
diamond powder was thus considered to be multimodal. The 100 g of
diamond powder was made up as follows: 5 g of average particle size
1.8 micro meters, 16 g of average particle size 3.5 micro meters, 7
g of average particle size 5 micro meters, 44 g of average particle
size 10 micro meters and 28 g of average particle size 20 micro
meters. This multimodal particle size distribution extended from
about 1 micro meter to about 30 micro meters.
[0159] The diamond powder had been rendered hydrophilic by prior
acid cleaning and washing in de-ionised water. To the suspension an
aqueous solution of cobalt nitrate and a separate aqueous solution
of sodium carbonate were simultaneously slowly added while the
suspension was vigorously stirred. The cobalt nitrate solution was
made by dissolving 125 grams of cobalt nitrate hexahydrate
crystals, Co(NO.sub.3).sub.2.6H.sub.2O, in 200 ml of de-ionised
water. The sodium carbonate solution is made by dissolving 45.5 g
of pure anhydrous sodium carbonate, Na.sub.2CO.sub.3 in 200 ml of
de-ionised water. The cobalt nitrate and sodium carbonate reacted
in solution precipitating cobalt carbonate CoCO.sub.3, as per the
following equation,
##STR00002##
[0160] In the presence of the suspended diamond powder particles,
with their hydrophilic surface chemistry, the cobalt carbonate
crystals nucleated and grew on the diamond particle surfaces. The
cobalt carbonate precursor compound for cobalt, took the form of
whisker shaped crystals decorating the diamond particle surfaces.
The sodium nitrate product of reaction was removed by a few cycles
of decantation and washing in de-ionised water. The powder was
finally washed in pure ethyl alcohol, removed from the alcohol by
decantation and dried under vacuum at 60.degree. C.
[0161] The dried powder was then placed in an alumina ceramic boat
with a loose powder depth of about 5 mm and heated in a flowing
stream of argon gas containing 5% hydrogen. The top temperature of
the furnace was 750.degree. C. which was maintained for 2 hours
before cooling to room temperature. This furnace treatment
dissociated and reduced the cobalt carbonate precursor to form pure
cobalt particles, with some carbon in solid solution decorating the
surfaces of the diamond particles. In this way it was ensured that
the cobalt particles were always smaller than the diamond particles
with the cobalt being homogeneously distributed. The conditions of
the heat treatment were chosen with reference to the standard
cobalt carbon phase diagram of the literature. At 750.degree. C. it
may be seen that the solid solubility of carbon in cobalt is low.
At these conditions the formation of amorphous non-diamond carbon
at this temperature is low and traces of non-diamond carbon could
be detected in the final diamond-metal particulate mass. The
resultant powder mass of multimodal diamond particles with an
overall 20 weight % of cobalt metal decorating the diamond particle
surfaces had a pale light grey appearance. The powder mass was
stored under dry nitrogen in an air-tight container to prevent
oxidation of the fine cobalt decorating the diamond surfaces.
[0162] For each rock removal body 11.4 g of the stock particulate
mass was then pre-compacted into a hemispherical ended tantalum
canister in a uniaxial hard metal compaction die to form a
semi-dense hemispherical ended right cylindrical body. The 12.75
weight % cobalt, tungsten carbide cylindrical substrate for each
body was inserted into a tantalum canister with wall thickness of
50 micro meters. The tantalum encompassed end of the substrate was
then inserted into the open end of the diamond mass containing
canister such that the end wall of the canister separated the
diamond mass from the substrate, and further uniaxial compacted to
form an assembly. After appropriate trimming of the open end of the
canisters, the assembly was inserted into a third canister of
slightly larger diameter, vacuum degassed and sealed under vacuum
using procedures known in the art. To consolidate further, to a
higher green density and to eliminate or radically reduce spatial
density variations, the canister assembly was then subjected to a
cold isostatic compaction procedure at a pressure of 200 MPa.
Several so called green body assemblies were produced in this
manner.
[0163] Each green body assembly was then placed in an assembly of
compactable ceramic, salt components suitable for high pressure
high temperature treatment as well established in the art. The
material immediately surrounding the encapsulated green body was
made from very low shear strength material such as sodium chloride.
This provides for the green bodies being subjected to pressures
which approach a hydrostatic condition. In this way pressure
gradient induced distortions of the green body may be
mitigated.
[0164] The green body canister assemblies were then subjected to a
pressure of 6 GPa and a temperature of approximately 1560.degree.
C. for 1 hour using a belt type high pressure apparatus as well
established in the art. During the end phase of the high pressure
high temperature procedure the temperature was slowly reduced over
several minutes to approximately 750.degree. C., maintained at this
value and then the pressure was reduced to ambient conditions. The
high pressure assembly was then allowed to cool to ambient
conditions before extraction from the high pressure apparatus. This
procedure during the end phase of the high pressure high
temperature treatment was thought to allow the surrounding salt
media to remain in a plastic state during the removal of pressure
and so prevent or inhibit shear forces bearing upon the now
sintered PCD body.
[0165] The fully dense, hemispherical ended right cylindrical
bodies were then brought to dimensions of 16 mm diameter and 27 mm
long by finishing procedure such as fine diamond grinding and
polishing as well established in the art.
[0166] In summary, one or more examples including polycrystalline
bodies not deriving their required metal from substrate materials
may be formed of PCD bodies of high homogeneity with their greatest
dimensions possibly being around 150 mm or more, limited only by
the design and scale of high pressure and high temperature
apparatus known in the art and currently available. In addition,
the PCD materials exploited in such examples may include PCD
material compositions not accessible using conventional PCD
manufacture, such as fine grained PCD with low metal contents,
coarse grain PCD with high metal contents, both outside the band
501 of FIG. 5. Also, the range and accuracy of composition of
highly specific alloys to aid the diamond particle sintering in the
examples may be significantly extended beyond those conventionally
accessible, the latter being largely restricted to the cementing
metal of sintered hard metal substrates. A potentially beneficial
consequence may be that the PCD bodies may be macroscopically
residual stress free at a scale greater than ten times the average
grain size of the PCD material where the maximum grain size is no
more than three times the average grain size. This distinguishes
such PCD bodies over conventional prior art PCD bodies made
attached to large substrates where, due to differential expansion
and contraction on return-to-room conditions during manufacture,
large and significant residual stress distributions may arise in
both the PCD volume and substrate volume of the overall body. These
large residual stress distributions involving both compressive and
tensile regions are taught to be the life determining aspects in
rock drilling applications. The PCD bodies of the examples
therefore may assist in increasing the life of cutters
incorporating such PCD bodies in rock drilling applications.
[0167] The rock removal bodies of the examples may maintain the
conventional overall shape of a simple right cylinder and the
well-established custom and practice of brazing these cylinders
into the housing bodies of the tools into which they are to be
inserted via the cemented hard metal substrate may also be
maintained. Thus, some of the examples may provide a means of
exploiting the key advantages of free standing PCD bodies but with
the inclusion of a substrate attached during the PCD material
manufacturing procedure. In this way, the standard extremely
well-established designs of drill bits and housing bodies together
with the brazing related attachment procedures may be exploited and
modifications and re-designs of such aspects may not be required.
Thus some examples thus concern the means of making rock removal
bodies, of general right cylindrical shape, where the attributes of
the procedures of making free standing PCD bodies are made use of
but substrates of general hard metal materials are attached in-situ
during the manufacturing procedures.
[0168] While various embodiments have been described with reference
to a number of examples, those skilled in the art will understand
that various changes may be made and equivalents may be substituted
for elements thereof and that these examples are not intended to
limit the particular embodiments disclosed.
REFERENCES
[0169] 1. Scott D E, Skeem M R, "Diamond enhanced shear cutting
elements on roller cone bits", Finer Points 2002 pp25-29
Fall-Winter and Proc Engineering Technology Conf on Energy,
Houston, Tex., 2001 Vol A pp121-135.
[0170] 2. Bridgman, P W, 1935, Physical Review, vol. 48, pages
825-832.
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