U.S. patent application number 14/752265 was filed with the patent office on 2015-10-15 for high diamond frame strength pcd materials.
The applicant listed for this patent is Smith International, Inc.. Invention is credited to John Daniel Belnap, Feng Yu.
Application Number | 20150292271 14/752265 |
Document ID | / |
Family ID | 47005567 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150292271 |
Kind Code |
A1 |
Yu; Feng ; et al. |
October 15, 2015 |
HIGH DIAMOND FRAME STRENGTH PCD MATERIALS
Abstract
The present disclosure relates to cutting elements incorporating
polycrystalline diamond bodies used for subterranean drilling
applications, and more particularly, to polycrystalline diamond
bodies having high diamond frame strength and methods for forming
and evaluating such polycrystalline diamond bodies. A
polycrystalline diamond body is provided, having a top surface, a
cutting edge meeting the top surface, and a first region including
at least a portion of the cutting edge. The first portion exhibits
a diamond frame strength of about 1200 MPa or greater, or about
1300 MPa or greater.
Inventors: |
Yu; Feng; (Lindon, UT)
; Belnap; John Daniel; (Lindon, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Smith International, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
47005567 |
Appl. No.: |
14/752265 |
Filed: |
June 26, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13449641 |
Apr 18, 2012 |
9091131 |
|
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14752265 |
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61476696 |
Apr 18, 2011 |
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Current U.S.
Class: |
51/307 |
Current CPC
Class: |
B24D 18/0009 20130101;
E21B 10/46 20130101; E21B 10/55 20130101 |
International
Class: |
E21B 10/55 20060101
E21B010/55; B24D 18/00 20060101 B24D018/00 |
Claims
1. A method of forming a wear-resistant polycrystalline diamond
cutting element, comprising: providing a powder mixture comprising
a plurality of diamond particles having an average particle size of
20 microns or less; compacting the powder mixture to compress the
diamond particles; and subjecting the powder mixture and a catalyst
material to a high temperature and high pressure sintering process
sufficient to form a polycrystalline diamond body, at least a
region of the polycrystalline diamond body comprising a
microstructure having a plurality of bonded-together diamond
crystals having a diamond frame strength of at least 1200 MPa,
wherein the sintering process comprises applying a pressure within
the range of approximately 7.0 to 8.2 GPa.
2. The method of claim 1, wherein the high temperature and high
pressure sintering process comprises applying a pressure of
approximately 7.0 GPa.
3. The method of claim 2, wherein the powder mixture comprises a
first mixture of diamond particles having an average particle size
in the range of 15-20 microns, and a second mixture of diamond
particles having an average particle size in the range of 2-4
microns, wherein the first mixture comprises approximately 80% of
the powder mixture, and the second mixture comprises approximately
20% of the powder mixture.
4. The method of claim 3, wherein the region of the polycrystalline
diamond body comprises a diamond volume fraction of at least
93%.
5. The method of claim 1, wherein the pressure is within the range
of approximately 7.0-7.5 GPa.
6. The method of claim 1, wherein the bonded-together diamond
crystals comprise a sintered grain size of approximately 5-7
microns.
7. The method of claim 1, further comprising: dividing the diamond
body into first and second portions; removing the catalyst material
from the first portion of the diamond body; and determining a
compressive stress in the first and second portions, wherein the
first portion comprises a drop in compressive stress of about
15-25% compared to the second portion.
8. A method of selecting a polycrystalline diamond body for
wear-resistant applications, comprising: obtaining a
polycrystalline diamond body comprising a material microstructure
comprising a plurality of bonded-together diamond crystals and
interstitial regions between the diamond crystals, the interstitial
regions comprising a catalyst material; substantially removing the
catalyst material from at least a first region of the diamond body;
ascertaining a flexural strength of the first region; and selecting
the diamond body for a wear-resistant application based on the
flexural strength of the first region of the diamond body, wherein
the flexural strength of the first region of the selected diamond
body is at least 1300 MPa, and wherein the increased flexural
strength results in an increased wear resistance at elevated
temperatures.
9. The method of claim 8, further comprising dividing the
polycrystalline diamond body into first and second portions and
removing the catalyst material from the first portion to form the
first region.
10. The method of claim 9, further comprising determining a
compressive stress in the first and second portions, wherein the
first portion comprises a drop in compressive stress of about
15-25% compared to the second portion.
11. A method for increasing a wear resistance of a polycrystalline
diamond body, comprising: obtaining a mixture of diamond particles;
sintering the mixture at high temperature and high pressure in the
presence of a catalyst material to form a polycrystalline diamond
body; and increasing a diamond frame strength of the
polycrystalline diamond body to at least 1300 MPa, wherein
increasing the diamond frame strength comprises at least one of
increasing the pressure for sintering the polycrystalline diamond
body to at least 7.0 GPa, or reducing an average particle size of
the diamond particles in the mixture to below 16 microns, wherein
the increased diamond frame strength results in an increased wear
resistance at elevated temperatures.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to and the benefit of U.S.
patent application Ser. No. 13/449,641, filed Apr. 18, 2012, titled
"High Diamond Frame Strength PCD Materials" and to U.S. Provisional
Application No. 61/476,696, filed Apr. 18, 2011, titled "High
Strength Diamond Frame PCD Materials and Shear Cutters Having
Cutting Edges Formed From Such Materials," the disclosures of which
are incorporated by reference herein in their entirety.
BACKGROUND
[0002] Polycrystalline diamond (PCD) materials known in the art are
formed from diamond grains (or crystals) and a catalyst material
which are subjected to high pressure and high temperature
conditions ("HPHT sintering process"). Such PCD materials are known
for having a high degree of wear resistance, making them a popular
material choice for use in such industrial applications as cutting
tools for machining and wear and cutting elements in subterranean
mining and drilling, where such high degree of wear resistance is
desired. In such applications, conventional PCD materials can be
provided in the form of a surface layer or body to impart desired
levels of wear resistance to a cutting tool.
[0003] Traditionally, PCD cutting elements include a substrate and
a PCD body or layer attached thereto. Substrates used in such
cutting element applications include carbides such as a cemented
tungsten carbide (e.g., WC--Co). Such conventional PCD bodies
utilize a catalyst material to facilitate intercrystalline bonding
between the diamond grains and to bond the PCD body to the
underlying substrate. Metals conventionally employed as the
catalyst are often selected from the group of solvent metal
catalysts including cobalt, iron, nickel, combinations, and alloys
thereof.
[0004] The amount of catalyst material used to form the PCD body
represents a compromise between desired properties of
strength/toughness/impact resistance and hardness/wear
resistance/thermal stability. While a higher metal catalyst content
typically increases the strength, toughness, and impact resistance
of a resulting PCD body, such higher metal catalyst content also
decreases the hardness and corresponding wear resistance as well as
the thermal stability of the PCD body. Thus, these inversely
affected properties ultimately limit the ability to provide PCD
bodies having desired levels of hardness, wear resistance, thermal
stability, strength, impact resistance, and toughness to meet the
service demands of particular applications, such as cutting and/or
wear elements used in subterranean drilling devices.
[0005] A particularly desired property of PCD bodies used for
certain applications is improved thermal stability during wear or
cutting operations. A problem known to exist with conventional PCD
bodies is that they are vulnerable to thermal degradation when
exposed to elevated temperature cutting and/or wear applications.
This vulnerability results from the differential that exists
between the thermal expansion characteristics of the solvent metal
catalyst material disposed interstitially within the PCD body and
the thermal expansion characteristics of the intercrystalline
bonded diamond. Such differential thermal expansion is known to
start at temperatures as low as 400.degree. C., and can induce
thermal stresses that can be detrimental to the intercrystalline
bonding of diamond and eventually result in the formation of cracks
that can make the PCD structure vulnerable to failure. Accordingly,
such behavior is not desirable.
[0006] Another form of thermal degradation known to exist with
conventional PCD materials is one that is also related to the
presence of the solvent metal catalyst in the interstitial regions
of the PCD body and the adherence of the solvent metal catalyst to
the diamond crystals. Specifically, the solvent metal catalyst is
known to cause an undesired catalyzed phase transformation in
diamond (converting it to carbon monoxide, carbon dioxide, or
graphite) with increasing temperature, thereby limiting practical
use of the PCD body to about 750.degree. C.
[0007] Thermal degradation can lead to chipping, spalling, partial
fracturing, and/or exfoliation of the PCD body. These problems can
be caused by the formation of micro-cracks within the PCD body
followed by propagation of the crack across the PCD body.
Micro-cracks can form from thermal stresses occurring within the
PCD body.
SUMMARY
[0008] The present disclosure relates to cutting elements
incorporating polycrystalline diamond bodies used for subterranean
drilling applications, and more particularly, to polycrystalline
diamond bodies having a high diamond frame strength. In various
embodiments disclosed herein, a cutting element with a
polycrystalline diamond body having a high diamond frame strength
has been found to correlate with improved wear resistance. Diamond
frame strength is the strength of the polycrystalline diamond
structure itself, without any secondary phase materials such as
cobalt or other catalysts. Due to the behavior of such secondary
phase materials at elevated temperatures, the strength of the
polycrystalline diamond body with secondary phase materials has
been determined not to correlate sufficiently with improved wear
resistance in the field. As described in further detail below, the
wear resistance of such cutting elements can be improved by
increasing the diamond frame strength and reducing the secondary
phase content in the polycrystalline diamond body.
[0009] In one embodiment, a cutting element includes a substrate
and a polycrystalline diamond body formed over the substrate. The
polycrystalline diamond body includes a top surface with a cutting
edge. The polycrystalline diamond body has a material
microstructure with bonded-together diamond crystals and
interstitial regions between the diamond crystals. A region of the
microstructure including the cutting edge has a diamond frame
strength of about 1200 MPa or greater, or about 1300 MPa or
greater, and has an average sintered grain size of less than 10
microns. In one embodiment, the cutting element is incorporated
into a downhole tool.
[0010] In one embodiment, a method of forming a wear-resistant
polycrystalline diamond cutting element is provided. The method
includes providing a powder mixture having diamond particles with
an average particle size of 20 microns or less. The method includes
compacting the powder mixture to compress the diamond particles,
and sintering the powder mixture and a catalyst material at high
temperature and high pressure, in the range of 7.0 to 8.2 GPa. The
sintering process forms a polycrystalline diamond body. A region of
the polycrystalline diamond body has a microstructure with a
diamond frame strength of at least 1200 MPa.
[0011] This summary is provided to introduce a selection of
concepts that are further described below in the detailed
description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used in limiting the scope of the claimed subject
matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiments of high diamond frame strength PCD materials are
described with reference to the following figures. The same numbers
are used throughout the figures to reference like features and
components.
[0013] FIG. 1 is a perspective view of a drill bit incorporating a
plurality of cutting elements according to an embodiment of the
present disclosure.
[0014] FIG. 2 is a perspective view of a cutting element including
a PCD body and a substrate according to an embodiment of the
present disclosure.
[0015] FIG. 3A is schematic representation of a region of a PCD
body including a catalyst material.
[0016] FIG. 3B is a schematic representation of a region of a PCD
body that is substantially free of a catalyst material, according
to an embodiment of the present disclosure.
[0017] FIG. 4 is a diagram of PCD strength for leached and
unleached PCD bodies.
[0018] FIG. 5 is a diagram of PCD strength versus drilling
temperature for four PCD bodies.
[0019] FIG. 6 is a diagram of PCD fracture strength for various PCD
bodies with the identified average particle size and sintering
pressure.
[0020] FIG. 7 is a diagram of PCD diamond frame strength for two
PCD bodies, each tested in leached and un-leached states.
[0021] FIG. 8 is a front and side view, respectively, of a cutting
element undergoing a vertical lathe test, according to an
embodiment.
[0022] FIG. 9 is a diagram of the results of the wear resistance
test of FIG. 8, performed on various PCD bodies according to an
embodiment.
[0023] FIG. 10 is a collection of images of the results of the wear
resistance test of FIG. 9, performed on three PCD bodies.
[0024] FIG. 11 is a diagram of the results of comparative field
testing of cutting element including PCD bodies according to an
embodiment of the present disclosure.
[0025] FIG. 12 is a cross-sectional view of an example embodiment
cutting element.
[0026] FIG. 13 is a cross-sectional view of another example
embodiment cutting element.
DETAILED DESCRIPTION
[0027] The present disclosure relates to cutting elements
incorporating polycrystalline diamond bodies used for subterranean
drilling applications, and more particularly, to polycrystalline
diamond bodies having high diamond frame strength and methods for
forming and evaluating such polycrystalline diamond bodies.
[0028] The following disclosure is directed to various embodiments.
The embodiments disclosed have broad application, and the
discussion of any embodiment is meant only to be exemplary of that
embodiment, and not intended to intimate that the scope of the
disclosure, including the claims, is limited to that embodiment or
to the features of that embodiment.
[0029] Certain terms are used throughout the following description
and claims to refer to particular features or components. As one
skilled in the art would appreciate, different persons may refer to
the same feature or component by different names. This document
does not intend to distinguish between components or features that
differ in name only. The drawing figures are not necessarily to
scale. Certain features and components herein may be shown
exaggerated in scale or in somewhat schematic form and some details
of conventional elements may not be shown in the interest of
clarity and conciseness.
[0030] In the following description and in the claims, the terms
"including" and "comprising" are used in an open-ended fashion, and
thus, should be interpreted to mean "including, but not limited
to."
[0031] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
[0032] Concentrations, quantities, amounts, and other numerical
data may be presented herein in a range format. It is to be
understood that such range format is used merely for convenience
and brevity and should be interpreted flexibly to include not only
the numerical values explicitly recited as the limits of the range,
but also to include all the individual numerical values or
sub-ranges encompassed within that range as if each numerical value
and sub-range is explicitly recited. For example, a numerical range
of 1 to 4.5 should be interpreted to include not only the
explicitly recited limits of 1 to 4.5, but also include individual
numerals such as 2, 3, 4, and sub-ranges such as 1 to 3, 2 to 4,
etc. The same principle applies to ranges reciting only one
numerical value, such as "at most 4.5", which should be interpreted
to include all of the above-recited values and ranges. Further,
such an interpretation should apply regardless of the breadth of
the range or the characteristic being described.
[0033] When using the term "different" in reference to materials
used, it is to be understood that this includes materials that
generally include the same constituents, but may include different
proportions of the constituents and/or that may include differently
sized constituents, wherein one or both operate to provide a
different mechanical and/or thermal property in the material. The
use of the terms "different" or "differ", in general, are not meant
to include typical variations in manufacturing.
[0034] Any patent, publication, or other disclosure material, in
whole or in part, that is said to be incorporated by reference
herein is incorporated herein only to the extent that the
incorporated material does not conflict with existing definitions,
statements, or other disclosure material set forth in this
disclosure. As such, and to the extent necessary, the disclosure as
set forth herein supersedes any conflicting material incorporated
herein by reference. Any material, or portion thereof, that is said
to be incorporated by reference herein, but which conflicts with
existing definitions, statements, or other disclosure material set
forth herein will only be incorporated to the extent that no
conflict arises between that incorporated material and the existing
disclosure material.
[0035] Referring to FIG. 1, a drill bit 10, specifically a fixed
cutter drill bit, is shown. The drill bit 10 includes a bit body
12, which may be formed of a matrix material, such as a tungsten
carbide powder infiltrated with an alloy binder material, or may be
a machined steel body. The bit body 12 includes a threaded
connection 14 at one end for coupling the bit 10 to a drilling
string assembly (not shown). The bit body 12 also includes a bit
face 29 having a cutting element support structure disposed thereon
which, in this example, comprises a plurality of blades 16
extending from the surface of the bit body. Each of the blades 16
includes a plurality of cutter pockets 26 formed therein along the
periphery to accept and support a cutting element 20 positioned
therein. Drilling fluid flow courses 19 are disposed between
adjacent blades.
[0036] The cutting elements 20 may include polycrystalline diamond
compact cutting elements, which may also be referred to as "PCD
cutters", "shear cutters" or "cutters" 20. A perspective view of a
cutting element 20 is shown, for example, in FIG. 2. Referring to
FIG. 2, a PCD body 22 is bonded to a substrate material 24 to form
the cutting element 20. The PCD body 22 has an upper surface 22a
and a side surface 22b. The upper surface 22a meets the side
surface 22b at a cutting edge 22c. The cutting edge is that portion
of the cutting element which engages the formation during drilling.
The cutting edge is illustrated in FIG. 2 as a sharp edge; however,
in one or more alternative embodiments, the transition between the
upper surface 22a and the side surface 22b may contain a beveled,
curved, or tapered surface.
[0037] Alternatively, a PCD body may be created without a
substrate, and optionally may be bonded to a substrate after HPHT
sintering, or may be incorporated into a cutting tool without the
use of a substrate. Catalyst material may be added to the diamond
powder mixture prior to sintering.
[0038] The PCD body 22 is sometimes referred to as a diamond body,
diamond table or abrasive layer. The PCD body 22 contains a
microstructure of randomly oriented diamond crystals bonded
together to form a diamond matrix phase and a plurality of
interstitial regions interposed between the diamond crystals. The
lower surface 25 of the PCD body 22 and the upper surface of the
substrate 24 form the interface 28. The cutting element 20 has a
central longitudinal axis 11. The cutting element illustrated in
FIG. 2 is depicted as cylindrical; however, it is to be understood
that any other shape may be suitable, such as ovoid, elliptical,
etc., and these other shapes are contemplated as being within the
scope of the present disclosure. In one or more other embodiments,
the cutting element 20 may be used without a substrate 24. In one
or more embodiments, the PCD body has an average thickness (between
the lower surface 25 and the upper surface 22a) of at least 1.0 mm,
suitably at least 1.5 mm, more suitably at least 2 mm, most
suitably in the range of from 1.5 mm to 5 mm, for example 2.25 mm,
2.5 mm, 2.75 mm, 3 mm, 3.25 mm, 3.5 mm, or 4 mm.
[0039] FIG. 3A schematically illustrates a region 310 of a PCD body
that includes a catalyst material. In particular, the region 310
comprises a plurality of bonded together diamond crystals 312,
forming an intercrystalline diamond matrix first phase, and
catalyst material 314 that is attached to the surfaces of the
diamond crystals and/or disposed within the plurality of
interstitial regions that exist between the bonded together diamond
crystals (i.e., the interstitial regions are at least partially
filled with catalyst material).
[0040] FIG. 3B schematically illustrates a region 322 of a PCD body
that is substantially free of the catalyst material. Like the PCD
region 310 illustrated in FIG. 3A, the region 322 includes a
material microstructure comprising a plurality of bonded together
diamond crystals 324, forming the intercrystalline diamond matrix
first phase. Unlike the region 310 illustrated in FIG. 3A, this
region 322 of the PCD body has been treated to remove the catalyst
material from the plurality of interstitial regions and, thus,
comprises a plurality of interstitial regions 326 that are
substantially free of the catalyst material, i.e., substantially
empty voids (pores). At least a portion of the pores may be
interconnected.
[0041] The term "filled", as used herein to refer to the presence
of the catalyst material contained in the interstitial regions of
the PCD body, is understood to mean that substantially all of the
volume of the interstitial regions (voids/pores) contain the
catalyst material (and tungsten carbide, and/or trace amounts of
other elements such as refractory materials, including Nb, Ta, and
Mo that may infiltrate into the PCD; these materials typically
react with carbon to form carbides). Also, tungsten carbide and/or
trace amounts of Fe or Cr may be present as a byproduct of diamond
powder processing. However it is to be understood that there may
also be a volume of interstitial regions within the same region of
the PCD body that do not contain the catalyst material, and that
the extent to which the catalyst material effectively fills the
voids or pores will depend on such factors as the particular
microstructure of the PCD body, the effectiveness of the process
used for introducing the catalyst material, removal of absorbed
gases from the surfaces of the diamond powders, and the desired
mechanical and/or thermal properties of the resulting PCD body.
[0042] According to one embodiment, a PCD body with high diamond
frame strength achieves a desired high level of wear resistance.
Previous attempts have been made to achieve a cutting element with
a PCD body that has both high strength and high wear resistance.
However, as mentioned above, these two properties tend to be
inversely related, with wear resistance being provided by higher
diamond content, and strength being provided by higher catalyst
content. Additionally, the strength of a PCD body (including both
the diamond and catalyst phases) at room temperature does not
necessarily correlate with good wear resistance and performance in
the field, where the PCD body is subjected to much higher drilling
temperatures.
Accordingly, an investigation was made into the correlation between
strength and wear resistance, in order to provide a PCD body that
accomplishes both desired properties.
[0043] Several PCD bodies were tested as shown in FIG. 4 to
identify the strength of the PCD body with and without the catalyst
phase. FIG. 4 shows a chart of the average flexural strength of
four different PCD bodies, identified as Examples 1-4. As used
herein the flexural strength refers to the material resistance
against fracture caused by bending stress. Each PCD body was
divided into two parts, and one part was subsequently leached to
remove the catalyst material from the PCD body. The average
flexural strength of each PCD body was measured by a 3-point
bending test. In the 3-point bending test, the PCD disks, 16 mm in
diameter and 1.3 mm in thickness, were cut by laser beam or by EDM
method into bars with dimensions of 2 mm.times.1.3 mm.times.8.3 mm.
The flexural strength of each bar was measured by the 3-point
bending test on a bench-top universal testing machine at room
temperature. The universal testing machine was made by Interactive
Instruments (704 Corporate Park, Scotia, N.Y. 12302), model number
K1-16. The load cell capacity is 1000 lb. The loading rate employed
in the bending test was 0.005 mm/minute. The resulting data was
plotted in FIG. 4. The leached PCD bodies are plotted on the left
side of each pair, and the unleached PCD bodies on the right. At
least 21 specimens were tested for each column in FIG. 4, and each
column provides the average across the tested specimens.
[0044] As shown in FIG. 4, the leached PCD body in each Example
exhibited a significant drop in strength as compared to its
unleached counterpart. The PCD body identified as Example 1 was
found to have a strength of 1398 MPa prior to leaching, and 1045
MPa after leaching. Examples 2, 3, and 4 had strengths of 1414 MPa,
1414 MPa, and 1372 MPa prior to leaching, respectively, and had
strengths of 971 MPa, 1054 MPa, and 922 MPa after leaching,
respectively. These numbers correspond to a drop in strength of
about 25%, 31%, 25%, and 33% for Examples 1-4, respectively.
Accordingly, in one embodiment, a PCD body exhibits a drop in
compressive stress of up to 25%, and in another embodiment up to
33%, after leaching.
[0045] The strength of the unleached PCD bodies includes the
strength contributed by both the diamond frame and the secondary
catalyst phase. The strength of the leached PCD bodies is the
diamond frame strength. This value measures the strength of the
sintered, bonded-together diamond grains that form the PCD
structure, without any contribution of the secondary catalyst
phase. The diamond frame is the microstructure of bonded diamond
grains themselves. The spaces within the diamond frame may be
infiltrated with catalyst material, as represented in FIG. 3A, or
may be empty, as represented in FIG. 3B.
[0046] The values in FIG. 4 identify a drop in strength from the
unleached PCD body (diamond frame and catalyst material) to the
leached PCD (the diamond frame). In order to confirm whether this
difference in strength was attributable to the removal of the
secondary catalyst phase, a compression test was also performed on
these same four Examples. The compressive stress of the PCD bodies
was measured by Raman spectroscopy. Additional details regarding
Raman spectroscopy can be found in U.S. Pat. No. 7,543,662. The
difference in compressive stress between the leached and unleached
PCD bodies for each Example was then identified. For Example 1, the
leached PCD body exhibited a compressive stress that was 368 MPa
less than its unleached counterpart. For Example 2, the difference
was 430 MPa, for Example 3 it was 389 MPa, and for Example 4 it was
441 MPa. In each case the leached PCD body exhibited less
compression than the unleached PCD body.
[0047] These differences in compression correspond in value to the
drop in strength identified in FIG. 4. In Example 1, the drop in
strength from the unleached to the leached PCD body is 353 MPa, in
Example 2 it is 443 MPa, in Example 3 it is 360 MPa, and in Example
4 it is 450 MPa. The drop in compression correlated closely to the
drop in strength. This indicates that the strength drop can be
attributed to the removal of the compressive stress induced by the
catalyst phase.
[0048] Thus, at room temperature, the presence of the catalyst
phase contributes to the measured strength of the PCD body.
However, as noted above, the wear resistance of PCD bodies with
high measured strength at room temperature has been less than
satisfactory in the field.
[0049] Based on the present investigation, a correlation was found
between the presence of the catalyst phase and a drop in strength
at high temperature. This relationship is shown in FIG. 5. FIG. 5
shows a plot of PCD strength versus drilling temperature, for four
different PCD bodies. Lines 1 and 3 are a PCD body sintered at a
first higher pressure, with line 1 representing the unleached PCD
body and line 3 the same PCD body after leaching. Lines 2 and 4 are
a PCD body sintered at a second lower pressure, with line 2
representing the unleached PCD body and line 4 the same PCD body
after leaching. To obtain the data for FIG. 5, the PCD flexural
strength data was collected at various temperatures. An individual
bend bar was first heated to the target temperature in a tube
furnace attached to the testing machine. The mechanical load was
then applied at the set temperature. The maximum load each bar
could support was recorded to calculate its flexural strength.
[0050] At room temperature, the unleached PCD bodies (lines 1 and
2) exhibit a higher strength than the leached PCD bodies (lines 3
and 4), confirming the testing shown in FIG. 4. However, as the
temperature increases, such as during a drilling operation in the
field, the unleached PCD bodies decline in strength more rapidly
than the leached PCD bodies, until the lines actually intersect and
the leached PCD bodies exhibit a greater strength. This transition
area where the lines intersect is highlighted by the dotted
rectangle. Depending on the particular PCD bodies, this transition
may take place around about 700-800.degree. C. Drilling temperature
continues to increase past this transition region, with some
temperatures in the field during drilling operations reaching about
1,000 to 1,200.degree. C.
[0051] The strength curves shown in FIG. 5 indicate that at high
operating temperatures, the leached PCD bodies exhibit better
strength than the unleached PCD bodies. This result is not
indicated by testing at room temperature, which tends to show a
better strength for the unleached PCD bodies that include a
catalyst phase. This room temperature testing is consistent with
the understanding that strength and wear resistance require a
balance between the relative content of catalyst material and
diamond. However, the behavior of these PCD bodies at high
temperature, as shown in FIG. 5, indicates that both strength and
wear resistance can be achieved at high temperature with leached
PCD bodies with particular characteristics.
[0052] Furthermore, the strength and compression testing summarized
above with respect to FIG. 4 indicates that the difference in
strength is attributable entirely to the removal of the catalyst
phase. Thus, the wear resistance at high temperature can be
correlated with diamond frame strength (the strength of the leached
PCD bodies) (see FIG. 5). This testing indicates that PCD bodies
with high diamond frame strength perform better at high
temperatures than other PCD bodies due to the transition of the
catalyst phase material with rising temperatures. At room
temperature, the catalyst material occupying the interstitial
regions between the bonded diamond grains exerts a compressive
force against the diamond grains. This compressive stress was
measured as discussed above for the PCD bodies in FIG. 4. If the
catalyst material is removed from the PCD body, the compression
measured in the PCD body also drops.
[0053] As the operating temperature increases (see FIG. 5), the
catalyst material and the diamond frame undergo differing thermal
expansion. As a result, it is believed that the compression
provided by the catalyst material deteriorates, becomes neutral,
and ultimately reverts into tension. This tension can cause damage
to the diamond frame, introduce thermal stresses, and reduce the
strength of the PCD body, as indicated by the downward curve of
lines 1 and 2 in FIG. 5. The result may be cracks in the PCD body,
fracture, material loss, and failure of the cutting element.
[0054] Thus, the performance of a PCD body at high operating
temperature can be correlated with the diamond frame strength,
rather than the room temperature strength of the diamond and
catalyst phase. As used herein, "diamond frame strength" is the
flexural strength of the diamond grains themselves, which can be
measured by testing the strength of a PCD body with catalyst
material removed from the interstitial spaces between the diamond
grains (i.e., after leaching). This diamond frame strength can be
determined by a 3-point bending test.
[0055] In order to investigate PCD with high diamond frame
strength, several PCD bodies were tested, with the results shown in
FIG. 6. FIG. 6 shows the flexural strength of the PCD bodies versus
the average particle size of the diamond powder pre-sintering. For
each average particle size, three PCD bodies were formed at three
different sintering pressures. The three sintering pressure are
indicated by the letters L, M, and H, with 25L corresponding to a
25 micron average particle size powder sintered at low pressure,
25M at medium pressure, and 25H at high pressure (low, medium, and
high being relative terms only, for this chart). For each particle
size, the low pressure was about 5.5-5.6 GPa, the medium pressure
was about 6.3-6.5 GPa, and the high pressure was about 6.7 GPa.
Finally, each PCD body was divided into two parts, and one part was
leached. Thus each PCD body is represented by two bars in FIG. 6,
with the bar on the left showing the unleached PCD body, and the
bar on the right showing the leached PCD body. At least 21
specimens were tested for each column in FIG. 6, and each column
provides the average across the tested specimens.
[0056] Although the unleached 5 micron PCD bodies exhibited the
highest strength measurements at room temperature, cutting elements
with these characteristics have been observed to under-perform in
the field. The leached samples (the right-hand bar of each pair)
have a lower strength at room temperature than the unleached
samples. It was noted that the PCD formed from the smaller particle
sizes tended to show a greater drop in strength from the unleached
to the leached samples, as compared to the higher particle sizes.
This is shown, for example, in the 9 micron and 5 micron PCD bodies
in FIG. 6--the difference in strength for these samples is greater
than for the other samples. Also, for the leached 9 and 5 micron
PCD bodies, the sintering pressure did not clearly correlate with
diamond frame strength. The 9L, 9M, and 9H and the 5L, 5M, and 5H
samples did not show a clear trend with pressure. These results
indicate that other factors in addition to sintering pressure, such
as particle size distribution and diamond packing, contribute to
the diamond frame strength.
[0057] In one embodiment, PCD bodies were prepared and subjected to
flexural strength and wear resistance tests to compare the wear
resistance of each. Two different diamond particle sizes were used,
forming first and second PCD bodies, referred to as PCD A and PCD B
below. PCD A was formed with diamond particles having an average
particle size of 12 .mu.m. PCD B was formed with diamond particles
having an average particle size of 9 .mu.m. Four bodies for PCD A
were formed, and two were leached. Four bodies for PCD B were
formed, and two were leached. All PCD bodies were HPHT sintered
under a pressure of about 67 kbar at a temperature between 1400 and
1500.degree. C.
[0058] The flexural strength of the leached and unleached PCD A and
PCD B bodies was measured by a three-point bending test, and the
results are shown in FIG. 7. PCD A exhibited an average flexural
strength of 1537 MPa unleached, and 1065 MPa leached, and PCD B
exhibited an average flexural strength of 1702 MPa unleached, and
1335 MPa leached. For the leached bodies, the flexural strength
represents the diamond frame strength.
[0059] FIG. 7 shows that PCD B exhibited a higher flexural strength
than PCD A. The average flexural strength of the PCD B bodies was
about 10% higher than PCD A for the unleached bodies, and about 25%
higher than PCD A for the leached bodies. Thus the smaller particle
size appeared to contribute to a higher flexural strength, with a
greater effect on the leached bodies than the unleached bodies. In
one embodiment, a PCD body is formed from a diamond particle
mixture having an average particle size of 9 .mu.m or less.
[0060] Additionally, FIG. 7 shows that the unleached bodies
exhibited higher flexural strength than the leached bodies, as
expected. The drop in strength from unleached to leached was about
30% for PCD A and 21% for PCD B. Thus, PCD B exhibited a smaller
relative drop in strength due to leaching, as compared to PCD
A.
[0061] The PCD A and PCD B samples were also subjected to a wear
resistance test. The wear resistance test was a vertical turret
lathe (VTL) test, which is shown schematically in FIG. 8. FIG. 8
shows front and side views of the VTL test. The test was conducted
by applying a load to the PCD body 22, which is positioned with the
cutting edge 22c in contact with a rock table 30. The rock table 30
is rotated about a vertical axis. The PCD body is advanced into the
rock table, cutting into the rock structure, at a feed rate of 0.1
inches per revolution of the table. In this particular set of
testing, the vertical turret lathe machine used was an Essex
Machine Tool Services S.O. 1224 56'' Bullard Dynatrol VTL with
GE/Fanuc 18i-TA CNC controls. The rock table 30 was made of barre
granite and had a diameter of 36 inches. The load applied to the
cutter ranged from 200 to 2,000 pounds to move the cutter at the
specified feed rate. As the test progressed, the PCD body cut
through the rock table, causing wear on the PCD body. The wear-flat
area on the PCD body was measured after each set of 5 passes (one
pass being equal to advancement of the PCD body by 0.02 inches into
the rock table).
[0062] The VTL wear resistance test was conducted on six of the PCD
bodies--the two unleached PCD A bodies, two leached PCD A bodies,
and two leached PCD B bodies. The unleached PCD B bodies were not
tested, due to the limited size of the rock table. The six samples
tested were all tested on the same rock table 30.
[0063] The results of this testing are shown in FIGS. 9 and 10.
FIG. 9 shows the wear-flat area of the PCD bodies versus the number
of passes of the VTL test. A higher wear-flat area indicates a
lower wear resistance. As shown in FIG. 9, the leached PCD B sample
exhibited the highest wear resistance, followed by the leached PCD
A sample. The unleached PCD A sample exhibited the lowest wear
resistance, and the largest wear-flat area. Thus, comparing FIGS. 7
and 9, although the unleached samples showed higher strength at
room temperature, the unleached PCD A sample exhibited the lowest
wear resistance. The leached samples, which showed a lower strength
at room temperature, showed less wear resistance during the VTL
test than the unleached PCD A bodies. Additionally, the smaller
particle size utilized in PCD B appeared to contribute to an
increased wear resistance, as compared to PCD A (FIG. 9).
[0064] Photographs of one unleached PCD A body, one leached PCD A
body, and one leached PCD B body were taken during the VTL testing,
and these photographs are shown in FIG. 10. These photographs show
that the leached PCD B body showed less wear than the other two,
and the unleached PCD A body showed the most wear. This testing
shows that unleached PCD had poorer wear resistance, despite higher
room-temperature strength. In the leached condition, the diamond
frame strength correlated with an increase in wear resistance (see
leached PCD B bodies). The wear flat observations also suggested
the PCD bodies with lower strength exhibited secondary wear
behavior (in addition to pure wear), which was fracturing or
flaking along the wear flat bottom line.
[0065] Additional testing was conducted to investigate correlations
between flexural strength and average starting particle size, as
well as sintering pressure. Two different starting particle sizes
were used to create PCD bodies, referred to as PCD C and PCD D
below. PCD C was formed with diamond particles having an average
starting particle size of 9 .mu.m. These particles were HPHT
sintered at two different sintering pressures to form PCD bodies.
PCD D was formed with diamond particles having an average starting
particle size of 16 .mu.m. These particles were also HPHT sintered
at two different sintering pressures. At least 21 samples of each
PCD body at each condition were tested to collect the flexural
strength data below.
[0066] For each type of PCD body, half of the samples were leached,
and the rest remained unleached. The samples were then subjected to
a 3-point bending test to determine the flexural strength. The
average flexural strength for each type of PCD body is provided in
Table 1 below.
TABLE-US-00001 TABLE 1 Average Sintering Average Flexural Starting
Particle Pressure Strength (MPa) PCD Size (.mu.m) (kbar) Unleached
Leached C 9 67 1563 .+-. 122 1106 .+-. 67 9 70-72 1679 .+-. 143
1166 .+-. 77 D 16 67 1389 .+-. 65 1076 .+-. 64 16 70-72 1520 .+-.
108 1208 .+-. 76
[0067] Table 1 indicates that higher flexural strength is
correlated with higher sintering pressure and with smaller starting
particle size.
[0068] Additional testing was conducted to investigate correlations
between flexural strength and particle size distribution (PSD). Two
different PSD's were used to create PCD bodies, referred to as PCD
E and PCD F. The PSD for each PCD body is shown in Table 2 below.
The diamond particles were HPHT sintered at a pressure of about 67
kbar and a temperature between 1400 and 1500.degree. C. to form PCD
bodies, and the PCD bodies were subjected to a 3-point bending test
to determine the flexural strength (unleached). These results are
shown in Table 2.
TABLE-US-00002 TABLE 2 Average Flexural Strength PCD PSD Recipe
(MPa)/unleached E (6-12 .mu.m) + (10-20 .mu.m): 88% 1456 .+-. 71
2-4 .mu.m: 12% F (6-12 .mu.m) + (10-20 .mu.m): 84% 1249 .+-. 97 2-4
.mu.m: 11% 0.5-1 .mu.m: 5%
[0069] Table 2 shows that the PSD affected the resulting flexural
strength of the sintered PCD body. In this case, the addition of
the smaller particles in PCD F appeared to negatively impact the
flexural strength. Accordingly an optimal PSD may be achieved that
correlates with an increased diamond frame strength. The average
starting particle size, PSD, and sintering pressure all contribute
to the resulting diamond frame strength.
[0070] Based on the above testing, a PCD body was created from
diamond particles with an average starting particle size of 9 .mu.m
and a sintering pressure between 70-72 kbar. The resulting PCD body
exhibited an unleached flexural strength of 1702.+-.120 MPa, and a
leached flexural strength (diamond frame strength) of 1335.+-.110
MPa.
[0071] In one embodiment, a PCD body with a diamond frame strength
of about 1300 MPa or greater provides a desirable combination of
wear resistance and strength. In one embodiment, the PCD body with
high diamond frame strength is formed by providing a diamond
particle powder mixture having an average particle size of about
7-9 microns and a Weibull distribution. The diamond powder is HPHT
sintered adjacent to a carbide substrate in a press at a pressure
of about 7.0-7.2 GPa. The resulting PCD body has a sintered diamond
grain size of about 5-7 microns and a diamond frame strength of
about 1300 MPa or greater, in one embodiment about 1375 MPa. This
PCD body exhibited a drop in compression after leaching of about
18-22%. The diamond frame strength can be verified by either
leaching the PCD body and measuring its strength (such as by a
3-point bending test), or by dividing the PCD body into two parts,
leaching one part, and measuring the strength of the leached part.
The unleached part may also be tested for strength, although its
measured strength at room temperature should be higher due to the
presence of the secondary catalyst phase. In one embodiment, the
leached part shows a diamond frame strength of at least 1300 MPa,
and the unleached part shows a combined diamond and catalyst
strength of at least 1500 MPa. The PCD body can be finished into
the desired geometry and incorporated into a cutting element for
use in the field.
[0072] In another embodiment, the diamond powder mixture includes
80% diamond particles having an average particle size in the range
of 15-20 microns, and 20% diamond particles having an average
particle size in the range of 2-4 microns. In another embodiment,
the diamond powder mixture includes 80% diamond particles having an
average particle size in the range of 16-17 microns, and 20%
diamond particles having an average particle size in the range of
2-3 microns. The diamond powder mixture is sintered at a pressure
of about 7.0 GPa, forming a PCD body with a diamond frame strength
of 1200 MPa or greater (or 1300 MPa or greater), a diamond volume
fraction of 93% or greater, and an average sintered grain size
between about 9-14 microns.
[0073] In one embodiment, a PCD body sintered at about 7.0 GPa or
greater comprises a diamond frame strength of about 1200 MPa or
greater, such as about 1300 MPa or greater, and the PCD body
exhibits a drop in compressive stress of about 15 to 25% after
leaching, at room temperature, such as about 18-22%. In one
embodiment the PCD body exhibits a drop in compressive stress of up
to 25%.
[0074] In one embodiment, a cutting element such as cutting element
20 in FIG. 2 includes a polycrystalline diamond body 22, which has
an interface surface, a top surface opposite the interface surface,
a cutting edge meeting the top surface, and a material
microstructure. The material microstructure includes
bonded-together diamond crystals and interstitial regions between
the diamond crystals. The microstructure has a first region that
includes at least a portion of the cutting edge. The first region
has a diamond frame strength of about 1300 MPa or greater. The
first region may extend throughout the entire PCD body, or through
only a portion of the PCD body. In one embodiment, the first region
extends through a portion of the PCD body that includes at least a
portion of the cutting edge.
[0075] According to an embodiment, the sintered PCD body with high
diamond frame strength has a sintered average diamond grain size of
less than 14 microns, and in another embodiment less than 10
microns, in another embodiment less than 7 microns, in another
embodiment about 6-7 microns, in another embodiment about 5-6
microns, in another embodiment less than 5 microns, and in another
embodiment about 2-4 microns.
[0076] As described herein, the temperatures used during the HPHT
sintering process may be in the range of from 1350.degree. C. to
1500.degree. C., for example 1400.degree. C. to 1500.degree. C., or
for example from 1400.degree. C. to 1450.degree. C. Temperatures
typically are kept around 1450.degree. C. or below, and are not
raised much beyond 1500.degree. C., due to the resulting reactions
in the surrounding cell materials (niobium/tantalum reactions and
salt-NaCl melt). HPHT sintering to create PCD with high diamond
frame strength may be performed at a slightly higher temperature
than other HPHT sintering processes.
[0077] The mixture of diamond grains (natural or synthetic) and
catalyst material may be subjected to sufficient HPHT conditions
for a period of time to sinter the diamond crystals forming the PCD
body, as described herein, and optionally, to bond the PCD body to
a substrate. Suitable internal cold cell pressures required to
obtain a desired diamond frame strength depend on several factors
such as the amount and type of catalyst present as well as the
particle size and distribution of the diamond crystals used to form
the PCD body, the diamond powder packing, and the addition of
graphite. In the various examples described herein, no graphite was
added to the powder mixtures. The diamond powders were subjected to
a 1280.degree. C. vacuum environment for 1-2 hours before
sintering. No graphite was detectable by subsequent examination of
the powder by Raman spectroscopy, which is well known in the art as
a standard carbon phase characterization technique.
[0078] According to an embodiment, the pressure applied during HPHT
sintering to achieve a PCD body with high diamond frame strength is
about or above 7.0 GPa, or in the range of about 7.0 to 8.2 GPa, or
7.0 to 7.2 GPa, or 7.0 to 7.5 GPa, or 7.5 to 8.0 GPa, or greater
than 8.0 GPa. The pressure applied may vary with the diamond
particle size. For example, in one embodiment, a diamond powder
mixture with an average particle size within the range of 10-25
microns is sintered at a pressure of about 7.5 GPa. In another
embodiment, a diamond powder mixture with an average particle size
of about 5-10 microns is sintered at a pressure of about 7.5-7.8
GPa. In another embodiment, a diamond powder mixture with an
average particle size of about 2-4 microns is sintered at a
pressure of 8.0 GPa or above, such as 8.0 GPa to 8.2 GPa.
[0079] In one embodiment, a method of forming a PCD body with high
diamond frame strength is provided. The method includes sintering
the diamond powder mixture at a pressure of at least 7.0 GPa or
greater. The diamond mixture includes a well-packed mixture of fine
diamond particles. The close packing of these fine particles and
the high sintering pressure creates a sintered microstructure with
high diamond content and strong diamond-to-diamond bonding. These
steps reduce the content of catalyst material in the sintered PCD
body, and thereby reduce the compression provided by the secondary
phase at room temperature. Reduction of the catalyst phase content
and the magnitude of compression from the catalyst phase in turn
reduces the dependence on cobalt compressive stress to produce high
strength, and thus is beneficial for creating a fine-grain sintered
PCD with high diamond frame strength.
[0080] After sintering, the method may optionally include leaching
all or a portion of the PCD body. When leaching is desired,
complete leaching can be achieved in the PCD sample by placing the
sample in an acid solution in a Teflon container, which is
contained within a sealed stainless steel pressure vessel and
heated to 160-180.degree. C. Containers suitable for such leaching
procedures are commercially available from Bergoff Products &
Instruments GmbH, Eningen, Germany. It is likely that pressures of
between 100-200 psi are achieved by heating under these conditions.
A standard acid solution which has been found to work
satisfactorily in leaching PCD material is made from reagent grade
acids and comprises a concentration of approximately 5.3 mol/liter
HNO.sub.3 and approximately 9.6 mol/liter HF, which is made by
ratio of 1:1:1 by volume of HNO.sub.3-15.9 mol/liter (reagent grade
nitric acid): HF-28.9 mol/liter (reagent grade hydrofluoric acid):
and water. Verification of the leaching process is performed by
examining the leached PCD sample with penetrating x-ray radiography
to confirm that the acid mixture penetrated the sample and that no
macro-scale catalytic metallic regions remain. Alternatively, the
PCD on a cutter containing a substrate can be leached using means
to protect the substrate from exposure to the acid and/or acid
fumes.
[0081] In one embodiment, a method of forming a PCD body with high
diamond frame strength includes tightly packing the diamond powder
pre-sintering. This is particularly useful for diamond particle
mixtures with a fine particle size, which otherwise may result in a
PCD structure with a large porosity. For a given sintering
pressure, increasing the average particle size leads to a decrease
in porosity in the sintered PCD body. This result is likely due the
fracturing of the larger diamond crystals during the HPHT
sintering. Finer diamond crystals are more resistant to fracturing
than the larger diamond crystals, which fracture and rearrange
themselves under pressure, compacting and packing more effectively
into the spaces between the crystals. Very small diamond particles
tend to be more difficult to compact and fracture during
sintering.
[0082] Thus, a PCD structure with very fine diamond grains may
include a larger relative porosity, with a weaker diamond frame and
a lower diamond frame strength. This fine grade, unleached PCD will
exhibit a high strength, due to the presence of the catalyst
material in the pores between the fine diamond grains. Room
temperature testing of the unleached fine PCD body shows promising
results, but the degradation of the catalyst phase into tension at
high operating temperatures can cause failure of the cutting
element, as explained above.
[0083] Thus, in one embodiment, in order to obtain a PCD body with
high diamond frame strength and a fine diamond grain structure, the
fine diamond particles are tightly packed prior to sintering, and
then HPHT sintering is performed under very high pressure, such as
pressures of at least 7.0 GPa. In another embodiment the pressure
is in the range of 7.0-8.2 GPa, and in another embodiment 7.0-7.2
GPa, and in another embodiment 7.0-7.5 GPa, and in another
embodiment 7.5-8.0 GPa, and in another embodiment greater than 8.0
GPa. Prior to sintering, the diamond particles may be
pre-compacted, such as by applying a pressure in the range of
100-200 MPa, or even up to 600 MPa, to tightly pack the diamond
powder.
[0084] The pre-sintered diamond powder may have a mono-modal or
multi-modal particle size distribution. If a catalyst material is
mixed with the diamond crystals, the catalyst material may be
provided in the form of a separate powder or as a coating on the
diamond particles.
[0085] In one embodiment, a PCD body with high diamond frame
strength is incorporated into a shear cutter with a cutting edge,
such as the cutting element 20 with cutting edge 22c shown in FIG.
2. The PCD body includes a region that incorporate at least a
portion of the cutting edge. This region of the PCD body has a high
diamond frame strength, such as at least 1300 MPa.
[0086] Due to thermal expansion of the diamond and catalyst phases
in the PCD body, the strength of the PCD body at room temperature
does not necessarily correlate with wear resistance at elevated
temperatures. According to embodiments of the present disclosure,
high pressure sintering and other techniques are used to provide a
PCD body with a high diamond frame strength, which shows improved
wear resistance at elevated temperatures. A shear cutter is
provided that incorporates this PCD material along at least a
portion of the shear cutter cutting edge, for improved wear
resistance.
[0087] In one embodiment, a PCD body with high diamond frame
strength also exhibits a high diamond content, or high diamond
volume fraction. PCD with high diamond content is described in more
detail in co-pending U.S. application Ser. No. 12/784,460, filed
May 20, 2010, published as U.S. Publication No. 2010/0294571, the
contents of which are hereby incorporated by reference. In one
embodiment, PCD with high diamond content may be formed through
HPHT sintering at higher than normal pressures, such as about 6.2
GPa to 7.1 GPa. In one embodiment, PCD with both high diamond frame
strength and high diamond content is formed through HPHT sintering
at even higher pressures, in the range of 7.2 GPa to 8.2 GPa, or
above 8.2 GPa. These pressures are the pressure at the increased
sintering temperature (i.e., not the cold cell pressure).
[0088] In various embodiments, a PCD body may have a first region
proximate the top surface, and a second region proximate the
interface with the substrate. At least the first region includes
PCD having a high diamond frame strength. In one embodiment, the
first region has diamond volume fraction of greater than 90% by
volume (% v), for example at least 91% v, at least 92% v, at least
92.5% v, at least 93% v, or at least 94% v in other embodiments. In
one or more embodiments, the cutting element has a first region
having a diamond volume fraction in the range of from greater than
90% v to 99% v, such as 93.5% v, 94.5% v, 95% v, 96% v, 97% v, or
98% v. In one embodiment, a first region of a PCD body includes a
sintered average grain size less than 25 microns and a diamond
volume fraction greater than 92%; and in another embodiment a
sintered average grain size of at most 15 microns and a diamond
volume fraction greater than 92.5%; and in another embodiment a
sintered average grain size in the range of from 2.5 to 12 microns
and a diamond volume fraction greater than 93%.
[0089] In one or more embodiments, a major portion (i.e., greater
than 50% by volume) of the second region of the PCD body may have a
lower diamond content (e.g. lower diamond volume fraction) than the
first region. In one or more embodiments, a major portion of the
second region of the PCD body may have a diamond volume fraction
more than 2% lower than the diamond volume fraction of the first
region (e.g., proximate the exterior surface of the PCD body), for
example at least 3% v or at least 4% v lower than the first region.
In this embodiment, the diamond volume fraction of the second
region may be at least 85%, for example in the range of from 85% to
95%, for example 87.5%, 90%, or 92%. The diamond content may change
in a gradient or step-wise manner within the PCD body.
[0090] In one embodiment, a PCD body with high diamond frame
strength may include first and second regions within the PCD body,
with different material characteristics. For example, the PCD body
may be leached to a certain depth to create a first leached region
and a second unleached region. The PCD body may be leached to any
depth. In one embodiment, the first leached region may extend at
least 300 microns within the diamond body, from the cutting edge.
Examples of suitable leach depths include 325 microns, 375 microns,
425 microns, 450 microns, 475 microns, 500 microns, 550 microns,
600 microns, 650 microns, 700 microns, 750 microns, 800 microns,
900 microns, or 1000 microns, or within a range of 300-600 or
300-1000 microns. Alternatively, the first leached region may
extend to a leach depth of at most 300 microns, such as 40 microns,
50 microns, 100 microns, 150 microns, 200 microns, 250 microns, or
within a range of 40-200, or 40-300 microns. The second region
within the PCD body containing catalyst material may have a
thickness that is sufficient to maintain a desired bond strength
between the PCD body and the material to which it may be attached
(e.g., the substrate). In one embodiment, a cutting element with a
cutting edge formed from PCD that has substantially empty
interstitial regions and a high diamond frame strength provides
superior performance.
[0091] In one embodiment, the first region of the PCD body having a
depth of at least 300 microns may extend along at least a "critical
zone" when viewed in vertical cross-section. The critical zone
extends along the length of the cutting edge and along the upper
surface of the PCD body for at least 1000 microns, for example at
least 12.5% of the diameter of the cutting element, measured from
the side surface, and at least 300 microns along the side surface,
measured along the side surface from the lower end of the cutting
edge. The critical zone also extends along at least a portion of
the circumferential distance of the PCD body. Suitably, the
critical zone may extend along a major portion of the
circumferential distance of the PCD body, such as along 25% of the
circumference. Suitably, the critical zone may extend along the
entire circumferential distance of the PCD body allowing the
cutting element to be reused on a drill bit without having to
undergo an additional treatment step.
[0092] In another embodiment, the first region extends along an
entire perimeter of the cutting element, and in another embodiment
it extends along the entire top surface, the cutting edge, and at
least a portion of a side surface. In another embodiment, the first
region extends throughout the polycrystalline diamond body.
[0093] In another embodiment, a PCD body with high diamond frame
strength may have a bilayer construction, including a first layer
proximate the cutting edge and a second layer proximate the
interface with the substrate. The second layer of PCD material
proximate the interface (the PCD "bilayer" or the "interlayer") has
more catalyst material and a lower diamond content than the
remainder of the PCD layer. This bilayer construction can be formed
using two or more diamond mixtures to form different layers of the
PCD body. Other options include powder mixtures having the same
average grain size but differing particle size distributions,
and/or powder mixtures incorporating differing amounts of premixed
solvent catalyst or other particulate additions such as tungsten or
tungsten carbide. For example, the diamond particle distribution
may be adjusted in the mixture near the interface with the
substrate, to provide a desired porosity in the second layer. In
another example embodiment, a larger amount of catalyst material
may be added to the diamond mixture in the second layer near the
substrate interface than in the one or more diamond mixtures used
to form the rest of the diamond body (e.g., the first layer). In an
example embodiment, the first layer of the diamond body may be
formed from one or more diamond mixtures having a different
particle size distribution than the one or more diamond mixtures
used to form the second layer of the diamond body. In additional
embodiments, three or more layers using different diamond mixtures
may be used.
[0094] The bilayer construction may be treated to remove the
catalyst material from a first region of the PCD body, such that
the first region has a plurality of substantially empty
interstitial regions. A second region may include catalyst material
in the interstitial regions. The first region may extend partially
through the first layer of the bilayer construction, all the way
through the first layer, or all the way through the first layer and
partially through the second layer.
[0095] Optionally, the PCD diamond body may be bonded to a
substrate. In one or more embodiments, the substrate may comprise a
metal carbide and a metal binder which has been sintered (also
referred to herein as a sintered metal carbide). Suitably, the
metal of the metal carbide may be selected from chromium,
molybdenum, niobium, tantalum, titanium, tungsten and vanadium and
alloys and mixtures thereof. For example, sintered tungsten carbide
may be formed by sintering a mixture of stoichiometric tungsten
carbide and a metal binder. The substrate may contain metal carbide
(e.g., tungsten carbide) in the range of from 75 to 98% by weight,
based on the total weight of the substrate, suitably from 80 to 95%
by weight, more suitably from 85 to 90% by weight. The amount of
metal binder may be in the range of from 5 to 25% weight (% w),
based on the total weight of the substrate, in particular from 5 to
15% w, for example 6% w, 8% w, 9% w, 10% w, 11% w, 12% w, 13% w, or
14% w, on the same basis. In one or more embodiments, the amount of
metal binder in present in the substrate may be in the range of
from 6% w to 9% w, or 9% w to 11% w, based on the total weight of
the substrate. A greater amount of metal binder in the substrate
may improve fracture toughness of the substrate while a lesser
amount of metal binder may improve wear resistance of the
substrate, in particular hardness, abrasion resistance, corrosion
resistance, and erosion resistance.
[0096] In one or more embodiments, diamond powder containing
diamond crystals or grains (natural or synthetic) may be placed
into an assembly with a source of catalyst material for the HPHT
sintering process. The source of catalyst material may be in the
form of a powder mixed with the diamond powder or in the form of a
coating on the diamond crystals. The amount of catalyst material
provided in combination with the diamond crystals (whether in the
form of a powder, tape, or other conformable material) may be in an
amount of at most 3% w, suitably at most 2% w. Alternatively, or in
addition, the source of catalyst material may be in the form of a
substrate positioned adjacent the diamond mixture in the
assembly.
[0097] In another embodiment, a PCD cutting element with high
diamond frame strength has a substrate with a reduced coefficient
of thermal expansion. This can be accomplished by reducing the
cobalt content of the substrate. In one embodiment, the cobalt
content of the substrate (prior to sintering) is within the range
of approximately 6% to 13% by weight. In another embodiment, the
cobalt content of the substrate is less than or equal to about 11%
by weight, and in another embodiment within the range of
approximately 9% to 11% by weight. This modification brings the
coefficients of thermal expansion of the substrate and the PCD
layer closer to each other, which reduces the thermal stresses at
the interface.
[0098] In one embodiment, the interface 28 between the PCD layer 22
and the substrate 24 has non-aggressive protrusions 36. The
interface may be flat or include a slight dome (with a height 32 to
diameter 30 ratio of at most 0.2, or at most 0.1, such as zero to
0.2 or zero to 0.1), and/or one or more non-aggressive protrusions
(FIG. 12). In one or more embodiments, the one or more
non-aggressive protrusions 36 have continuously contoured surfaces.
In one or more embodiments, the interface surface of the substrate
has only non-aggressive protrusions 36 thereon, such as protrusions
with a protrusion ratio (the height 40 to width 38 ratio of the
protrusion) less than 0.7 (FIG. 13). The non-aggressive protrusions
are intended to reduce stress concentrations that can lead to
cracks in the PCD layer along the interface. In another embodiment,
the interface has a smooth surface devoid of protrusions and
depressions. In one embodiment, the interface is a flat surface,
without a dome, protrusions, or depressions (height to diameter
ratio of zero).
[0099] The high diamond content PCD bodies disclosed above may be
formed as a cutting element, such as a shear cutter, for
incorporation into a downhole tool such as a drill bit. Such
cutting elements as described herein may be used in any number of
applications for example downhole tools such as reamers, bi-center
bits, hybrid bits, impregnated bits, roller cone bits, milling
bits, as well as other downhole cutting tools.
[0100] As used herein, the term "catalyst material" is understood
to refer to materials that were used to initially form the diamond
layer (i.e., bond the diamond particles together), and can include
materials identified in Group VIII of the Periodic table (e.g.,
cobalt). The catalyst material may be selected from Group VIII
elements of the Periodic table (CAS version in the CRC Handbook of
Chemistry and Physics), in particular selected from cobalt, nickel,
iron, mixtures thereof, and alloys thereof, such as cobalt.
[0101] As used herein, the term "removed" is used to refer to the
reduced presence of a specific material in the interstitial regions
of the diamond layer, for example the reduced presence of the
catalyst material used to initially form the diamond body during
the sintering or HPHT process, or metal carbide present in the PCD
body (a metal carbide, such as tungsten carbide, may be present
through addition to the diamond mixture used to form the PCD body
(for example from ball milling the diamond powder) or through
infiltration from the substrate used to form the PCD body). It is
understood to mean that a substantial portion of the specific
material (e.g., catalyst material) no longer resides within the
interstitial regions of the PCD body, for example the material is
removed such that the voids or pores within the PCD body may be
substantially empty. However, it is to be understood that some
small amounts of the material may still remain in the
microstructure of the PCD body within the interstitial regions
and/or remain adhered to the surface of the diamond crystals.
[0102] By "substantially free of added catalyst material", it is
understood to mean that no catalyst material, other than catalyst
material left as an impurity from manufacturing the diamond
crystals, is added to the diamond mixture. That is, the term
"substantially free", as used herein, is understood to mean that a
specific material is removed, but that there may still be some
small amounts of the specific material remaining within
interstitial regions of the PCD body. In an example embodiment, the
PCD body may be treated such that more than 98% by weight (% w of
the treated region) has had the catalyst material removed from the
interstitial regions within the treated region, in particular at
least 99% w, more in particular at least 99.5% w may have had the
catalyst material removed from the interstitial regions within the
treated region. 1-2% w metal may remain, most of which is trapped
in regions of diamond regrowth (diamond-to-diamond bonding) and is
not necessarily removable by chemical leaching.
[0103] The term "substantially empty", as used herein, is
understood to mean that at least 75% of the volume of a void or
pore is free from a material such as a catalyst material or metal
carbide, suitably at least 85% v, more suitably at least 90% v is
free from such materials. The quantity of the specific material
remaining in interstitial regions after the PCD body has been
subjected to treatment to remove the same can and will vary on such
factors as the efficiency of the removal process, and the size and
density of the diamond matrix material. The specific material to be
removed from the PCD body may be removed by any suitable process.
Treatment methods include chemical treatment such as by acid
leaching or aqua regia bath and/or electrochemical treatment such
as by an electrolytic process. Such treatment methods are described
in US2008/0230280 A1 and U.S. Pat. No. 4,224,380, which methods are
incorporated herein by reference. Treatment by leaching is also
discussed in more detail below.
[0104] The average grain size of a PCD sample can be determined by
an electron back scatter diffraction (EBSD) technique, as follows.
A suitable surface preparation is achieved by mounting and
surfacing the PCD sample using standard metallographic procedures,
and then subsequently producing a mirror surface by contact with a
commercially available high speed polishing apparatus (available
through Coborn Engineering Company Limited, Romford, Essex, UK).
The EBSD data is collected in a scanning electron microscope
suitably equipped to determine grain orientation by localized
diffraction of a directed electron beam (available through EDAX
TSL, Draper, Utah, USA). Magnification is selected such that
greater than 1000 grains are included in a single image analysis,
which was typically between 500.times.-1000.times. for the grain
sizes examined. Other conditions may be as follows: voltage=20 kV,
spot size=5, working distance=10-15 mm, tilt=70.degree., scan
step=0.5-0.8 microns. Grain size analysis is performed by analysis
of the collected data with a misorientation tolerance
angle=2.degree.. Defined grain areas determined according to the
above conditions are sized according to the equivalent diameter
method, which is mathematically defined as GS=(4A/.PI.) 1/2, (that
is, the square root of 4A/.PI.), where GS is the grain size and A
is the grain area.
[0105] Suitably, leaching agents include materials selected from
inorganic acids, organic acids, mixtures and derivatives thereof.
The particular leaching agent used may depend on such factors as
the type of catalyst material used, and the type of other
non-diamond metallic materials that may be present in the PCD body.
In an example embodiment, suitable leaching agents may include
hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3)
and mixtures thereof. In one or more embodiments, the PCD body has
a microstructure such that it requires at least 3 days under
standard conditions, described below, to leach substantially all
the catalyst material from the interstitial regions in the PCD body
in the first region, to a depth of 300 microns.
[0106] In one or more embodiments, one or more cutting elements of
the present disclosure (first cutting elements) may be positioned
on the bit alone or in combination with one or more second cutting
elements which are different (i.e., not in accordance with the
cutting elements of the present disclosure). The cutting elements
of the present disclosure may be positioned in one or more areas of
the drill bit which will benefit the most from the improved
properties/performance of such cutting elements. Such areas of the
drill bit may include the nose region, shoulder region and/or gage
region of the drill bit. In one or more embodiments, the cutting
elements of the present disclosure may be positioned on the drill
bit as primary cutting elements in the nose, shoulder and/or gage
regions while the second cutting elements may be positioned on the
drill bit as back-up cutting elements in these regions as well as
primary cutting elements in the cone region. In one or more
embodiments, the cutting elements of the present disclosure may be
positioned on the drill bit as primary cutting elements and as
back-up cutting elements in the nose, shoulder and/or gage regions
of the drill bit while the second cutting elements may be
positioned as primary cutting elements in the cone region.
[0107] According to an embodiment of the disclosure, cutting
elements with PCD bodies having high diamond frame strength were
incorporated into drill bits and field tested for performance
ratings. The results of the field testing is shown in FIG. 11. The
data for this figure was compiled from 31 bit runs, which were
tested by drilling the bits to 14,000 feet at rates of 30-70
feet/hour. The state of the drill bits and the cutting elements on
the drill bit was assessed and compared to a prior bit with a
standard PCD cutter. This prior PCD cutter included a PCD body with
similar diamond grain size, HPHT sintered at a lower pressure than
the tested cutters, and leached. The 31 tested drill bits included
cutting elements with PCD bodies exhibiting a leached average
flexural strength of 1335.+-.110 MPa. These PCD bodies included an
average starting particle size of 9 .mu.m, and a PSD similar to PCD
E (shown in Table 2 above). The PCD bodies were HPHT sintered at a
sintering pressure of 70-72 kbar.
[0108] FIG. 11 shows the results of the field testing. A drill bit
was determined to be "Average" for a particular parameter if it
matched the performance of the prior, comparative cutter. The
number of bits coming at Average, Above Average, and Below Average
was noted for each performance parameter. The performance
parameters in FIG. 11 include the following: Run-Rating (overall
combined performance); Footage Rating (distance traveled, i.e.,
drilling depth), Rate of Penetration (ROP) Rating (rate of
advancement of the bit into the hole); C/S Rating (quality of the
bit cutting structure after drilling); and Dull Rating (wear on
individual cutting elements on the drill bit). FIG. 11 shows that
in every category, a majority of the tested bits met or exceeded
the comparative Average. Only a small percentage of the tested bits
resulted in Below Average ratings.
[0109] Accordingly, in an embodiment, cutting elements of the
present disclosure having high diamond frame strength can drill
through an earthen formation for longer periods of time and/or at
higher speeds, higher weight on bit (WOB), and/or higher rates of
penetration (ROP) than cutting elements known heretofore. According
to various embodiments, the cutting elements of the present
disclosure can drill through highly abrasive earthen formations
(e.g., sandstones and geothermal applications) which were not
amenable to drilling with fixed cutter drill bits heretofore.
[0110] In one embodiment, a method for determining a wear
resistance of a polycrystalline diamond cutting element is
provided. The polycrystalline diamond body includes a material
microstructure comprising a plurality of bonded-together diamond
crystals, and a catalyst material occupying the interstitial
regions between the diamond crystals. The method includes dividing
the diamond body into first and second portions, and substantially
removing the catalyst material from the first portion of the
diamond body, such as by leaching. Then, the first portion of the
diamond body is subjected to a strength test, such as a 3-point
bending test, to determine the flexural strength of the first
portion. The method includes selecting the diamond body for
wear-resistant applications, such as shear cutting applications,
based on an increased flexural strength. In one embodiment, the
increased flexural strength of the first portion of the diamond
body is at least 1300 MPa. The increased flexural strength
identifies an increased wear resistance at elevated
temperatures.
[0111] In one embodiment, a method for increasing a wear resistance
of a polycrystalline diamond body is provided. A mixture of diamond
particles is obtained and HPHT sintered in the presence of a
catalyst material to form PCD. To increase the wear resistance of
the PCD, the method includes increasing the diamond frame strength
of the PCD to at least 1300 MPa. The diamond frame strength can be
increased by increasing the sintering pressure to at least 7.0 GPa,
and/or by reducing the average particle size of the diamond
particles in the mixture to below 16 microns. The increased diamond
frame strength identifies an increased wear resistance of the PCD
at elevated temperatures.
[0112] While the present disclosure has been described with respect
to a limited number of embodiments, those skilled in the art,
having benefit of this disclosure, will appreciate that other
embodiments and modifications can be devised which do not
materially depart from the scope of the invention as disclosed
herein. All such embodiments and modifications are intended to be
included within the scope of this disclosure as defined in the
following claims.
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