U.S. patent application number 09/923513 was filed with the patent office on 2002-01-24 for drill bit inserts with interruption in gradient of properties.
Invention is credited to Huang, Sujian J., Yong, Zhou.
Application Number | 20020007972 09/923513 |
Document ID | / |
Family ID | 23128067 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020007972 |
Kind Code |
A1 |
Yong, Zhou ; et al. |
January 24, 2002 |
Drill bit inserts with interruption in gradient of properties
Abstract
A cutter element for use in a drill bit, comprising a substrate
and a plurality of layers thereon. The substrate comprises a grip
portion and an extending portion. The layers are applied to the
extending portion such that at least one of the layers is harder
than at least one of the layers above it. The layers can include
one or more layers of polycrystalline diamond and can include a
layer in which the composition of the material changes with
distance from the substrate.
Inventors: |
Yong, Zhou; (Spring, TX)
; Huang, Sujian J.; (The Woodlands, TX) |
Correspondence
Address: |
CONLEY ROSE & TAYON, P.C.
P. O. BOX 3267
HOUSTON
TX
77253-3267
US
|
Family ID: |
23128067 |
Appl. No.: |
09/923513 |
Filed: |
August 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09923513 |
Aug 7, 2001 |
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09293190 |
Apr 16, 1999 |
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6315065 |
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Current U.S.
Class: |
175/374 ;
175/426; 76/108.2 |
Current CPC
Class: |
E21B 10/573
20130101 |
Class at
Publication: |
175/374 ;
175/426; 76/108.2 |
International
Class: |
E21B 010/62 |
Claims
What is claimed is:
1. An insert for use in a drill bit, comprising: a substrate
supporting at least three layers, said layers comprising: an
ultrahard layer; a relatively soft layer comprising a material that
is less wear resistant than said ultrahard material; and a first
additional layer; wherein at least one of said layers interrupts a
gradient in a mechanical property of the layers, the mechanical
property being selected from: the moduli of elasticity, wear
resistances, hardnesses, strengths, and coefficients of thermal
expansion of the layers.
2. The insert according to claim 1 wherein said first additional
layer is above said ultrahard layer.
3. The insert according to claim 1 wherein said first additional
layer comprises an ultrahard material.
4. The insert according to claim 1 wherein said first additional
layer comprises tungsten carbide and is positioned between said
relatively softer layer and said substrate.
5. The insert according to claim 1 wherein said ultrahard layer
comprises PCD and said first additional layer comprises tungsten
carbide and is positioned above said PCD layer.
6. The insert according to claim 1, further including a second
additional layer.
7. The cutting element according to claim 1 wherein said cutting
surface is axisynunetric.
8. The cutting element according to claim 1 wherein said cutting
surface is hemispherical.
9. The cutting element according to claim 1 wherein said cutting
surface is not axisymmetric.
10. The cutting element according to claim 1 wherein said interface
surface is not axisymmetric.
11. The cutting element according to claim 1 wherein said
relatively soft layer is more wear resistant than said
substrate.
12. A cutter element for use in a drill bit, comprising: a
substrate; a layer of ultrahard material affixed to said substrate;
and a relatively soft layer affixed to said ultrahard layer such
that said ultrahard layer is between said substrate and said
relatively soft layer.
13. A cutter element for use in a drill bit, comprising: a
substrate; a layer of PCD; and a cushion layer affixed to said
substrate and supporting said PCD layer and having a gradient of
hardness such that a first portion of said cushion layer is harder
than a second portion of said cushion layer, said first portion
being between said second portion and said substrate.
14. The insert according to claim 13 wherein said first additional
layer comprises a composite of ultrahard material, cobalt and
tungsten carbide containing a greater proportion of tungsten
carbide particles away from said substrate and a greater proportion
of ultrahard material near said substrate.
15. The insert according to claim 13, further including an
additional layer.
16. The insert according to claim 13 wherein said ultrahard
material comprises polycrystalline diamond.
17. The cutting element according to claim 13 wherein said cutting
surface is axisynunetric.
18. The cutting element according to claim 13 wherein said cutting
surface is hemispherical.
19. The cutting element according to claim 13 wherein said cutting
surface is not axisymmetric.
20. The cutting element according to claim 13 wherein said
interface surface is not axisymmetric.
21. A method for constructing a cutter element, comprising: (a)
providing a substrate having a grip portion and an extending
portion; (b) providing a plurality of layers on the extending
portion such that at least one of the layers is harder than at
least another one of the layers.
22. The method according to claim 21 wherein step (b) comprises
providing a layer comprising a composite of ultrahard material,
cobalt and tungsten carbide containing a greater proportion of
tungsten carbide particles away from said substrate and a greater
proportion of ultrahard material near said substrate.
23. The method according to claim 21 wherein step (b) includes
providing a layer of PCD.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to cutting elements
for use in earth-boring drill bits and, more specifically, to a
means for increasing the life of cutting elements that comprise one
or more layers of ultrahard material, such as diamond, affixed to a
substrate and having one or more softer, intermediate layer(s)
therebetween. Still more particularly, the present invention
relates to a polycrystalline diamond enhanced cutter insert
including a substrate and a plurality of layers on the substrate,
wherein the layers include an ultrahard layer supported on an
additional layer, and wherein at least one of the layers is harder
and/or more wear resistant than at least one of the layers above
it.
BACKGROUND OF THE INVENTION
[0002] In a typical drilling operation, a drill bit is rotated
while being advanced into a soil or rock formation. The formation
is cut by cutting elements on the drill bit, and the cuttings are
flushed from the borehole by the circulation of drilling fluid that
is pumped down through the drill string and flows back toward the
top of the borehole in the annulus between the drill string and the
borehole wall. The drilling fluid is delivered to the drill bit
through a passage in the drill stem and is ejected outwardly
through nozzles in the cutting face of the drill bit. The ejected
drilling fluid is directed outwardly through the nozzles at high
speed to aid in cutting, flush the cuttings and cool the cutter
elements.
[0003] The present invention is described in terms of cutter
elements for roller cone drill bits. In a typical roller cone drill
bit, the bit body supports three roller cones that are rotatably
mounted on cantilevered shafts, as is well known in the art. Each
roller cone in turn supports a plurality of cutter elements, which
cut and/or crush the wall or floor of the borehole and thus advance
the bit.
[0004] Conventional cutting inserts typically have a body
consisting of a cylindrical grip portion from which extends a
convex protrusion. In order to improve their operational life,
these inserts are preferably coated with an ultrahard material such
as polycrystalline diamond. The cutting layer typically comprises a
superhard substance, such as a layer of polycrystalline diamond,
thermally stable diamond or any other ultrahard material. The
substrate, which supports the coated cutting layer, is normally
formed of a hard material such as tungsten carbide (WC). The
substrate typically has a body consisting of a cylindrical grip
from which extends a convex protrusion. The grip is embedded in and
affixed to the roller cone and the protrusion extends outwardly
from the surface of the roller cone. The protrusion, for example,
may be hemispherical, which is commonly referred to as a semi-round
top (SRT), or may be conical, or chisel-shaped, or may form a ridge
that is inclined relative to the plane of intersection between the
grip and the protrusion. The latter embodiment, along with other
non-axisymmetric shapes, is becoming more common, as the cutter
elements are designed to provide optimal cutting for various
formation types and drill bit designs.
[0005] The basic techniques for constructing polycrystalline
diamond enhanced cutting elements are generally well known and will
not be described in detail. They can be summarized as follows: a
carbide substrate is formed having a desired surface configuration
and then placed in a mold with a superhard material, such as
diamond powder and/or its mixture with other materials which form
transition layers, and subjected to high temperature and pressure,
resulting in the formation of a diamond layer bonded to the
substrate surface.
[0006] Although cutting elements having this configuration have
significantly expanded the scope of formations for which drilling
with diamond bits is economically viable, the interface between the
substrate and the diamond layer and/or the transition layers
continues to limit usage of these cutter elements, as it is prone
to failure. Specifically, it is not uncommon for diamond coated
inserts to fail during cutting. Failure typically takes one of
three common forms, namely spalling/chipping, delamination and
wear. External loads due to contact tend to cause failures such as
fracture, spalling, and chipping of the diamond layer. Internal
stresses, for example thermal residual stresses resulting from the
manufacturing process, tend to cause delamination between the
diamond layer and the substrate or the transition layer, either by
cracks initiating along the interface and propagating outward, or
by cracks initiating in the diamond layer surface and propagating
catastrophically along the interface. Excessively high contact
stresses and high temperatures, along with a very hostile downhole
environment, also tend to cause severe wear to the diamond
layer.
[0007] One explanation for failure resulting from internal stresses
is that the interface between the diamond and the substrate or a
transition layer is subject to high residual stresses resulting
from the manufacturing processes of the cutting element.
Specifically, because manufacturing occurs at elevated
temperatures, the differing coefficients of thermal expansion of
the diamond and substrate material transition layer result in
thermally-induced stresses as the materials cool down from the
manufacturing temperature. These residual stresses tend to be
larger when the diamond/transition-layer/substrate interfaces have
smaller radii of curvature. At the same time, as the radius of
curvature of the interface increases, the application of cutting
forces due to contact on the cutter element produces larger
debonding and other detrimental stresses at the interface, which
can result in delamination. In addition, finite element analysis
(FEA) has demonstrated that during cutting, high stresses are
localized in both the outer diamond layer and at the
diamond/transition-layers/tungsten carbide interfaces. Finally,
localized loading on the surface of the inserts causes rings or
zones of tensile stress, which the PCD layer is not capable of
handling.
[0008] In addition, the cutting elements are subjected to extremes
of temperature and heavy loads when the drill bit is in use. It has
been found that during drilling, shock waves may rebound from the
internal interface between the two layers and interact
destructively.
[0009] The primary approach used to address the delamination
problem in convex cutter elements is the addition of transition
layers made of materials with thermal and elastic properties
located between the ultrahard material layer and the substrate,
applied over the entire substrate protrusion surface. These
transition layers have the effect of reducing the residual stresses
at the interface and thus improving the resistance of the inserts
to delamination. An example of this solution is described in detail
in U.S. Pat. No, 4,694,918 to Hall, which is incorporated herein in
its entirety.
[0010] Transition layers have significantly reduced the magnitude
of detrimental residual stresses and correspondingly increased
durability of inserts in application. Nevertheless, basic failure
modes still remain. These failure modes involve complex
combinations of three mechanisms. These mechanisms are wear of the
PCD, surface initiated fatigue crack growth, and impact-initiated
failure.
[0011] The wear mechanism occurs due to the relative sliding of the
PCD relative to the earth formation, and its prominence as a
failure mode is related to the abrasiveness of the formation, as
well as other factors such as formation hardness or strength,
magnitude of contact stress, and the amount of relative sliding
involved during contact with the formation. The fatigue mechanism
involves the progressive propagation of a surface crack, initiated
on the PCD layer, into the material below the PCD layer until the
crack length is sufficient for spalling or chipping. Lastly, the
impact mechanism involves the sudden initiation and propagation of
a surface crack or internal flaw initiated in the PCD layer or at
the interface, into the material below the PCD layer until the
crack length is sufficient for spalling, chipping, or catastrophic
failure of the enhanced insert.
[0012] All of these phenomena are deleterious to the life of the
cutting element during drilling operations. More specifically, the
residual stresses, when augmented by the repetitive stresses
attributable to the cyclical loading of the cutting element by
contact with the formation, may cause spalling, fracture and even
delamination of the diamond layer from the transition layer or the
substrate. In addition to the foregoing, state of the art cutting
elements often lack sufficient diamond volume to cut highly
abrasive formations, as the thickness of the diamond layer tends to
be limited by the resulting high residual stresses and the
difficulty-of bonding a relatively thick diamond layer to a curved
substrate surface even with the conventional layout of the
transition layers. For example, even within the diamond layer,
residual stresses arise as a result of temperature changes. Because
these stresses typically increase as the thickness of the layer
increases, this factor tends to be viewed as limiting on
thickness.
[0013] Hence, it is desired to provide a cutting element that
provides increased wear resistance and life expectancy without
increasing the risk of spalling or delamination.
SUMMARY OF THE INVENTION
[0014] The present invention provides a cutting element with
increased wear resistance and life expectancy and decreased risk of
spalling and delamination. The present cutter element includes at
least one transition layer that has mechanical properties that do
not lie on a gradient between the mechanical properties of the
outermost layer and those of the substrate. The outermost layer or
the surface layer may not be the hardest layer in terms of
mechanical properties. The present cutter element compensates for
the resulting residual stresses that might otherwise occur at the
non-intermediate layer by providing an interface geometry that
balances the reduction in bending stress that results from an
decreased radius of curvature with the increase in interface
delamination stresses resulting from a decreased radius of
curvature.
[0015] The non-intermediate layer of the present invention can be
either a discrete layer or can comprise a gradient or portion of a
gradient within a single layer, so long as direction of the
gradient is reversed with respect to adjacent layers. In each
instance, one objective of the present invention is to provide an
interruption or reversal of the gradient in at least one of the
following properties: the moduli of elasticity, wear resistances,
hardnesses, strengths, and coefficients of thermal expansion of the
layers so that at least one of the softer and less wear resistant
layers is supported by a harder and/or more wear resistant
layer.
[0016] One preferred embodiment of the present invention comprises
a substrate supporting at least three layers, with the layers
comprising an ultrahard layer, a relatively soft layer of a
material that is less wear resistant than the ultrahard, and a
first additional layer, wherein at least one of the layers
interrupts a gradient in a mechanical property of the layers. The
mechanical properties include the moduli of elasticity, wear
resistances, hardnesses, strengths, and coefficients of thermal
expansion of the layers.
[0017] Another preferred embodiment comprises a substrate having a
layer of ultrahard material affixed thereto and a relatively soft
layer affixed to the ultrahard layer such that the ultrahard layer
is between said substrate and said relatively soft layer.
[0018] Still another embodiment comprises a substrate and a layer
of PCD, with a cushion layer supporting the PCD layer. The cushion
layer has a gradient of hardness such that a first portion of
cushion layer next to the substrate is harder than a second portion
of said cushion layer that is next to the PCD layer.
[0019] Still another embodiment of the invention comprises a method
for constructing a cutter element, by providing a substrate having
a grip portion and an extending portion and providing a plurality
of layers on the extending portion such that at least one of the
layers is harder than at least another one of the layers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] For a detailed description of a preferred embodiment of the
invention, reference will now be made to the accompanying Figures,
wherein:
[0021] FIG. 1 is a cross sectional view of a cutting element
constructed in accordance with a first embodiment of the invention;
and
[0022] FIG. 2 is a cross sectional view of a cutting element
constructed in accordance with a second embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] As used in this specification, the term polycrystalline
diamond and its abbreviation "PCD" refer to the material produced
by subjecting individual diamond crystals to sufficiently high
pressure and high temperature that intercrystalline bonding occurs
between adjacent diamond crystals. An exemplary minimum temperature
is about 1300.degree. C. and an exemplary minimum pressure is about
35 kilobars. The minimum sufficient temperature and pressure in a
given embodiment may depend on other parameters such as the
presence of a catalytic material, such as cobalt, with the diamond
crystals. Generally such a catalyst/binder material is used to
assure intercrystalline bonding at a selected time, temperature and
pressure of processing. As used herein, PCD refers to the
polycrystalline diamond including cobalt. Sometimes PCD is referred
to in the art as "sintered diamond."
[0024] Also as used herein, the terms "beneath" and "above" are
used to refer to the relative positions of layers on the substrate.
The terms refer to the relative positions as shown in the Figures,
wherein the inserts are drawn with their grip portions downward, so
that "beneath" refers to positions closer to the substrate and
"above" refers to positions that are farther from the
substrate.
[0025] Referring initially to FIG. 1, a cross sectional view of a
cutting element 10 constructed in accordance with a first
embodiment of the invention comprises a substrate 12, and a cutting
layer 14. Substrate 12 comprises a body having a grip portion 16
and an extension portion 18. Grip portion 16 is typically
cylindrical, although not necessarily circular in cross-section,
and defines a longitudinal insert axis 17. Extension portion 18
includes an interface surface 19, which has an apex 20. According
to one preferred embodiment, substrate 12 comprises tungsten
carbide.
[0026] Cutting layer 14 is affixed to interface surface 19 and has
an outer, cutting surface 15, which has an apex 22. Cutting layer
14 comprises at least two layers having differing physical
properties. As discussed above, it is known to provide an outermost
layer comprising polycrystalline diamond (PCD) and cobalt and one
or more transition layers comprising diamond crystals, cobalt and
tungsten carbide, so long as the proportion of diamond crystals in
the material decreases inwardly towards the substrate and the
transition layer(s) provides a gradient, or transition, between the
mechanical properties of the substrate and the mechanical
properties of the outermost layer. It will be understood that,
while apices 20 and 22 are shown coincident with insert axis 17,
the present invention can practiced on inserts for which this is
not the case.
[0027] It has been discovered, however, that significant advantage
can be realized from the placement of a harder layer behind or
beneath at least one of the softer and/or less brittle layers.
Reference to this layer herein as the "non-intermediate layer"
refers to the fact that this layer interrupts the gradient in
either the modulus of elasticity, wear resistance, coefficient of
thermal expansion, hardness, strength, or any combination of these
properties, that would otherwise be formed by the other layers on
the cutter element and the substrate body itself. It will be
understood that this layer is nevertheless positioned between two
other layers or between one layer and the substrate.
[0028] By way of example, FIG. 1 shows an outermost PCD layer 26,
beneath which is a transition layer 28. In one embodiment,
transition layer 28 comprises a mixture of diamond crystals, cobalt
and precemented tungsten carbide particles. For example, transition
layer 28 might comprise between about 20 and about 80 percent by
volume diamond crystals, from about 20 to about 60 percent by
volume tungsten carbide, and between 5 and 20 percent cobalt.
Transition layer 28 may ranges in thickness from zero around its
edges to about 100 microns or more at its thickest. One preferred
technique for setting or capping the thickness of the transition
layer is to define it relative to the insert diameter. For example,
the thickness of thickest portion of the layer is preferably no
more than 40%, and preferably less than 30%, of the insert diameter
and still more preferably less 20% of the insert diameter. It will
be understood that the thickness of transition layer 28 may vary
across its area, and need not be axisymmetric.
[0029] Still referring to FIG. 1, in a preferred embodiment a
third, non-intermediate layer 38 is included between transition
layer 28 and substrate surface 19. In accordance with the present
invention, third layer 38 is harder and more wear resistant, and
has a higher modulus of elasticity or higher hardness than layer
28. For example, layer 38 can comprise the same PCD material as
outermost layer 26. Alternatively, layer 38 can comprise between
about 20 and about 80 percent by volume diamond crystals, from
about 20 to about 60 percent by volume tungsten carbide, and
between 5 and 20 percent cobalt. In a preferred embodiment, the
thickness of layer 38 equal to about 2-30% of the substrate
diameter at its thickest point. It will be understood that the
thickness of transition layer 38 may vary across its area, and need
not be axisymmetric.
[0030] When layer 38 comprises PCD, the insert exhibits less
residual stress on the interfaces between layers 28 and 38 and also
between layers 26 and 28 when a larger radius of curvature is
designed over interface surface 19. The insert also exhibits less
Hertz contact tensile stress. In addition, the second diamond layer
serves as a back-up wear layer that can extend the life of the
insert in the event of failure of the outermost layer. The softer
layer 28 serves as a cushion to absorb impact energy and allows the
total diamond thickness to be increased without the increase in
residual stresses that occur when the thickness of a single diamond
layer is increased.
[0031] In another alternative embodiment, layer 38 comprises a
conventional transition layer and layer 28 comprises a material
having a smaller modulus of elasticity and/or decreased wear
resistance as compared to layer 38, such as a transition layer with
a higher tungsten carbide and cobalt content. In this embodiment
again layer 38 interrupts the gradient in the mechanical properties
that is defined by outermost layer 16 and layer 28.
[0032] In still another alternative embodiment, outermost layer or
composite diamond 26 comprises the mixture of tungsten carbide and
PCD or another material that is softer than PCD, for example a
diamond composite. In this embodiment, it is preferred that layer
28 comprise PCD and layer 38 comprise a second transition layer. In
this embodiment, the outermost layer 16 can function to absorb
impact energy, while the diamond layer 28 provides stiffness to
reduce contact stress and also provides extended wear life after
outermost layer is worn away.
[0033] An alternative construction to that shown in FIG. 1 is
illustrated in FIG. 2, in which transition layers 28 and 38 are
replaced by a single layer 48. Layer 48 comprises a composite of
diamond crystals, cobalt and tungsten carbide containing a lesser
proportion of diamond crystals near the outer PCD layer 16 and a
greater proportion of diamond crystals near the substrate surface
19. This graded layer can be used in any of the various embodiments
described above. While the currently preferred embodiment comprises
two distinct layers 28, 38, any number of layers can be used, as
long at least one layer or portion of a layer interrupts the
gradient in mechanical properties between the substrate and at
least one layer or portion of a layer above the layer in
question.
[0034] The various embodiments of the present invention can be used
in conjunction with various interface shapes and cutter element
shapes. Hence, the cutter element shapes to which the principles of
the present invention can be applied are not limited to the
embodiments shown. For example, the basic shape of the cutter
element need not be axisymmetric and can vary, including SRT,
conical, chisel-shaped or relieved shapes, and have positive or
negative tangents. In addition, the shape of the outer surface of
the cutting layer can vary from those illustrated and the thickness
of each layer can vary from point to point. In each instance, the
present invention contemplates optimizing the shape of the
interface between the cutting layer and the substrate so as to
balance the residual stresses that result from manufacturing with
the stress distribution from mechanical loading. This optimization
allows substantial gains to be made in the localized enhancement of
the cutting layer, thereby increasing cutter life.
[0035] While the cutter elements of the present invention have been
described according to the preferred embodiments, it will be
understood that departures can be made from some aspects of the
foregoing description without departing from the spirit of the
invention. For example, while the outer abrasive cutting surface of
the cutting element of this invention is described in terms of a
polycrystalline diamond layer, other materials, for example, cubic
boron nitride, diamond composite, or a combination of superhard
abrasive materials, may also be used for the cutting surface of the
abrasive cutting element. Likewise, while the preferred substrate
material comprises cemented or sintered carbide of one of the Group
IVB, VB and VIB metals, which are generally pressed or sintered in
the presence of a binder of cobalt, nickel, or iron or the alloys
thereof, it will be understood that alternative suitable substrate
materials can be used.
* * * * *