Note: Descriptions are shown in the official language in which they were submitted.
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SMD 2-259
S~PPORTED POLYCRYSTALLINE COMPACrS
Back~round of the Invention
The present invention relates to the preparation of supported polycrystalline
diamond or cubic boron nitride (CBN) compacts and especially to the preparation of
such compacts configured for use as wire dies.
A polycrystalline compact is a sintered polycrystalline mass of abrasive
5 diamond and/or CBN particles bonded together to form an integral, tough, coherent,
high strength mass. The preparation of diamond compacts is disclosed, for example,
in U. S. Patent No. 3,141,746. CBN compacts are described, for example, in U S.
Pats. Nos. 3,136,615 and 3,233,988. A supported polycrystalline compact is a
compact attached to a reinforcing or substrate material such ~s cemented metal
10 carbide. In one configuration referred to as a supported wire die compact, a core of
polycrystalline diamond or CBN is jacketed by ~n annular support of, for example,
cemented carbide or stainless staeL
Supported compa^ts often are formed in a singIe step in situ process such as
described in U. S. Pats. Nos. 3,745,623, 3,831,428, 3,767,371,~ and 3,743,489. In such
15 a process, a metal (such as cobalt) which serves as the cementing agent of the
cemented carbide support flows under high temperature and pressure into the
polycrystalline mass to act therein as a catalyst for the formation of crystal-to-
- crystal bonds. One problem which may occur in such a single step process, and
especially in the production of a wire drawing die compact with an ann~ar support,
20 involves cementing agent/catslyst depletion at the polycrystalline diamond orCBN/support interface. Thus, in the case of a cobalt-cemented tungsten carbide
supported wire die compact, if there is sn excessive flow of cobalt from the carbide
support ring, a depleted zone or ring may develop in the carbide accompsnied by
micro-cracks extending into the support materiaL In addition, a single step process
25 affords no opportunity to separately inspect the unsupported polycrystalline mass.
As a result, if any defect should occur in either the compact or in the support
material, the entire assembly must be rejected rather than just the defective
component. Similarly, system parameters in sn in situ process need to be adjusted
to optimize the formation of the composite whole, and cannot be adjusted to
30 optimize the formation of the individual components. Finally, such single step
processes require that both the beginning crystPlline material and the support
material be subjected to highly elevated temperature and pressure conditions
sufficient to forrn the polycryst~lline mass. As a result, there is a significant
decrease in press throughput as compared to operations pressing just the crystalline
35 material.
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Although less frequently employed, two step processes wherein a compact is
first formed and is then attached to a support also are known. Thus, the use of a
bra~ing material for attachment purposes is described in the aboYe noted U.S. Pat.
No. 3,141,746. Similarly, supported wire die compacts made with a pre-formed
5 cylindrical polycrystalline core around which an annular jacket of metal support
material (e.g. stainless steel) is shrink-fitl:ed in place have been used successfully.
HoweYer, existing two step processes for the formation of supported polycrystalline
compacts pose certain difficulties. In the brazed approach one problem is to
adequately wet the crystalline surfaces to which the support is attached. The
10 situation is aggravated further in a morle recent form of polycrystalline diamond
compact termed the thermally stable compact as disclosed in U S. Pats. Nos.
4,224,380 and 4,288,2~8, since a thermally stable compact can comprise a porous,nearly pure diamond material. Even in the successful shrink-fitting two-step wir0
die process mentioned above, it would be beneficial ~o improve the strength of the
15 attachment between the compact and the surrounding metal support. In addition,
shrink-fitting by its nature requires the maintenance o close tolerances between
the parts to be joined. Naturally, this restriction adds to the difficulty and cost of
manufacture.
20 Broad Statement of the Invention
_
One object of the present invention, then, is to form supported polycrystalline
compacts including supported thermPlly stable polycrystalline diamond compacts.
-Such object is accomplished by separately forming both a polycrystPlline compact
haYing a surface, and a metal carbide or other plastically deformable support having
25 a support surface. The compact and support then are mated at their respectivesurfaces and subjected to pressure and temperature conditions sufficient to
plastically deform the support into attachment (chemical, physical or a combination)
with the compact. While conditions may be varied and optimized depending on the
materials used, attachment conditions will be sufficient if the temperature
30 employed is adequate to place the support material in a plastie state; the pressure is
adequate to deîorm the plasticized material into intimate contact with the compact
surface; and the combination of temperature, pressure and time is inadequate to
cause substantial or significant degradation of the polycrystalline diamond or cubic
boron nitride (CBN) compact. As can be appreciated, the required conditions
35 beneficially can be less than those required for an in situ process. Sustantial or
significant degradation comprehends the dimunition of performance properties of
the compact making it unsuitable for its intended use.
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The attachment of the support to the polycrystalline mass apparently involves
a physical component resulting from the mis-match in thermal expansion (contra~
tion) characteristics between the respective materials, and particularly because of
the relatively low expansion coefficient of the polycrystalline materials involved.
When the resulting product is recovered by return to ambient conditions, the support
material normally will exert a radial compression on the polycrystalline compactsupported thereby. In a wire die configuration, the support annulus beneficiallyexerts both a radial and an axial compression against the central polycrystalline
core. The attschment between the support and the polycrystalline mass also may
involve a chemical component if the materials at their mating surfaces are
interactive.
In~another aspect of the present invention, an interface material may be
placed between the compact and support prior to processing in order to control the
nature and degree of the attachment between the compact and the support. In
addition, the use of such an interface material can help minimi~e the machining of
the support and of the compact which may bè required before attachment in order
to ensure a proper fit. Another advantage is the ability to place the polycrystalline
diamond or CBN compact under variable and controllable compressive loading by a
carbide support, e.g., in order to match or maximize carbide grade characteristics~
Another advantage is the ability to support thermally stable compacts. With respect
to thermally-stable polycrystalline diamond compacts, the use-of interface materi-
als, such as those exhibiting a reduced melting point and which are more reactive
with carbon, can improve the bonding between the compact and the support
materiaL Suitable interface materials include cobalt or other catalysts or solvents
in cornbination with boron or a mixture thereof with other carbide formers whichfurther increases the reactivity of interface materials under conditions of the
process. Such reactive interface materials are thought to be useful in view of the
difficulty noted above which works against the bonding of carbide support material
to thermally stable compacts.
Further advantages oves single step in situ processes include the ability to
increase high temperature/high pressure apparatus throughput since only the pre-formed polycrystalline compact need be exposed to diamond-forming conditions.
Also, non-conforming compacts may be rejected separately in the pre-form state
rather than in the final supported state. Additionally, more freedom is a-~ailable in
the selection of carbide grades than in the in situ process owing to the absence of
the cobalt-depletion phenomena noted above. These other advantages will be
readily apparent based on the disclosure contained herein.
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Detailed Description of the Invention
The supported polycrystalline diamond or CBN compacts of the present
invention are unique in several respects. Thus, the products possess physical
properties which replicate the physical properties of conventionally sintered sup-
5 ported compacts wherein the support is provided in situ. ~or exampls, compacts ofthe present invention have a level of w)iform compressive loading not found in
brazed or shrink-fitted supported compacts. Concomitantly, incidences of cobalt or
other catalyst or solvent depletion from carbide substrates which are possible in situ
prepared supported compacts are substantially eliminated and characteristics of the
10 tungsten carbide (WC) or other carbide substrate thereby are more uniformly
maintained. Moreover, the process of the present invention can be applied to
thermally stable polycrystalline compacts which further enhsnces the utility of the
present invention.
Under the temperature and pressure of operation of the present invention, WC
15 or other carbide substrate material becomes plastic or plastically deformable so
that the respective mating surfaces of the support and polycrystalline compact are
placed in intimate contact. Plastic for present purposes comprehends moldable,
pliable, and/or resilient. Plastically deformable, then~ comprehends a deforming or
molding operation wherein the material returns substantially to its original con-
20 figuration, i.e. the material has a degree of memory. Because the substrate isplastic under the conditios of operation, virtually no harm is done to the substrate
or to the polycrystalline compact. Of course, this assumes that conditions of
operation will be substantially preclusive to graphitization of the diamond or
reconversion of cubic boron nikide to its hexagonal or other form. Once the
25 required time at temperature and pressure has been reached, heating of the reaction
cell within which the supported compact is disposed is ceased and pressure is
released. Upon cooling, the polycrystalline material contracts much less than the
carbide support. Such thermal expansion differential between the core and the
support causes the polycrystalline core to be loaded compressively and remain
30 firmly attached to the carbide support. In a conventional compact configuration
(e.g. such as in U.S. Pat. No. 3,745,623), a carbide support in the present invention-
exerts a compressive radial force against the diamond or CBN core to which it isattached. In a wire drawing die configuration, the polycrystalline core is loeded
compressively both radially and axially. Additionally, diamond~to-carbide bonding is
35 thought to contribute to this attachment.
Broadly, conditions of operation of the present invention are such that the
support is plastically deformed. In terms of temperature, the support must be
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rendered plastic. In terms of pressure, the plastic support must be moved or
deformed. Such conditions of operation Qdvantageously include a temperature, a
pressure, and a time such that the polycrystalline or CBN compact is not subjected
to conditions whereat significant reconversion of the superabrasive particles occurs
5 (e.g. graphitization of diamond), or is otherwise damaged. Accordingly, the process
preferably will be conducted at a temperature and at a pressure which- may be
within the diamond stable or CBN stable region. For diamond, the temperature
ranges from between about 1000 to about 2000C at a pressure which may be in
excess of 40 Kbars (e.g. 40-80Kbars). For CBN, similar temperatures and pressures
lO apply. Within such stable regions, conditions of temperature and pressure typically
will be on the lower ends of the ranges as the polycrystalline compacts already are
sintered. In fact, it may be possible to operate the processes under conditions
outside of the diamond or CBN stable region provided that such conditions ~re
maintained for a length OI time insufficient to cause noticeable damage to the
15 polycrystalline cores. In this regard, the process is practiced for time periods which
are typically much less than time periods encountered industrially in the manu-
facture of polycrystalline compacts. Accordingly, for polycrystalline diamond
compacts, a pressure of about 40-50 Kbars may be used but may not be necessary,
and a temperature of about 1000-1300C may be maintained for time periods
20 typically not e~:ceeding a few minutes. Shorter time periods~also m~y be used. -The
same conditions apply generally for CBN compacts also. Since less demanding
processing parameters are required, use of lower temperature and pressure presses
than in the producffon of polycrystalline compacts is enabled. Alternatively, it may
be possible to extend the serviceable life of the existing high pressure apparatus by
25 operating under less demanding conditions than required for in situ processes.
Polycrystalline diamond compacts which may be supported in accordance with
the present invention are well-known in the art and methods for making such
polycrystalline diamond compacts are detailed, for example, in U5. Pat. No.
3,141,746. Briefly, diamond crystals or particles are placed adjacent a source of
30 catalyst or solvent and then subjected to high pressure and high temperature
conditions for a time sufficient to bond or sinter the diamond crystals together.
While the relative shape of the abrasive mass and catalyst can be varied, typically
the abrasive mass will be cylindrical and the catalyst will be a disk placed on top of
or below the diamond mass or an annulus which surrounds the cylinder of abrasive35 crystals. The catalyst or solvent generally is cobalt, nickel, or iron with cobalt
being pref erred. Alternatively, the catalyst can be selected ~rom any known
catalyst which also includes ruthenium, rhodium, palladium, platinum, chromium,
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manganese, tantalum, osmium, iridium, or mixtures or alloys thereof. The catalyst
may be admixed with the abrasive cystals in addltion to or instead of being a
separate mass placed adjacent to the abrasive crystals.
Cubic boron nitride compacts are manufactured in a manner quite similar to
5 that described for polycrystalLine diamond compacts. In the case of CBN compacts7
however, the metal swept into the CBN crystal mass may or may not be a catalyst
or solvent for CBN recrystallization. I'he HP/HT sintering process for CBN is
carried out in the CBN stable region which is in the range of pressure and
temperature conditions under which the CBN is thermodynamically stable. Methods
10 for making CB~I compacts can be found in U5. Pats. Nos. 3,233,988, 3,743,489, and
3,~67,371.
As noted above, the manufacture of thermally stable compacts is described in
U S. Pats. Nos. 4,288,248 and 4,224,380. Substantially all of the metallic (cfltalyst)
`phase from polycrystal~ine dismond or CBN compacts has been removed to yield a
15 compact comprising self-bonded diamond or CBN particles with an interconnected
network of pores dispersed throughout. Thermally stable compacts can withstand
exposure to temperatures of about 1200-1300C in a non-oxidizing atmosphere
without substantial thermal degradation, giving them an advantage over conven-
tional compacts which are marked by the onset of thermal degradation at a
20 temperature of between about 700 and about 900C at atmospheric pressure.
The support or substrate to which the polycrystalline compacts are bonded or
~oined generally is ~ metal carbide substrate with metals generally selected from
the group consisting of tungsten, titanium, tantalum, molybdenum, and mixtures
thereof; however, other materials (e.g. ceramics or metals) may be used as support
25 materials. Preferably, the carbide molding powder will be a cemented metal
carbide powder with the cementing metal ~eing selected from cobalt, nickel, ironand mixtures thereof, as is well known in this art. Cobalt cemented tungsten
carbide is the materi~1 of choice for making the support material to which the
polycrystalline compact is attached. In this regard, conventional supported poly-
30 crystalline compacts often rely on the carbide support for providing a sollrce of
catalyst/solvent which sweeps through the abrasive crystals for forming the
polycrystalline diarnond or CBN compact which is in situ bonded to the substrate for
support. The use of the catalysttsolvent from the support material is well known in
both the typical cylindrical and wire die configurations. The present invention
35 permits the use of metal carbide supports low in cobalt content, which carbide
grades are harder and stiffer (higher elastic modulus), hence closer to the diamond
in stiffness which means better support for the diamond core. Such low cobalt
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carbide grades, however, are less tough than metal carbide supports containirg ahigher concentration of cobalt (cobalt being referred to by illustration rather than
limitation). The Pltering of the metal carbide support composition is permitted
more readily by the present invention because the support can be attached to an
5 already sintered polycrystalline compact under conditions wherein no
cataiyst/solvent need be present.
Theoretically, the pre-sintered polycrystalline diamond or CBN compacts may
be in any desired configuration or geometry as can the substrate which may be pre-
sintered also or may be only pressed into a shape desired for matching the
l0 configuration of the polycrystalline compact. The wire die configuration having a
polycrystalline compact core and annular support is most preferred for the applica-
tion of the invention. Both the support and the polycrystalline compact should have
surfaces which are adapted to be mated. Mating of such surfaces merely connotes
placing the support and compact adjacent each other. The mated compact and
15 support then may be placed within the reaction cell of an HP/HT apparatus, such as
those found in the patent3 cited above with respect to the manufacture of
polycrystalline diamond and CBN compacts.
On occasion, a polycrystalline core for use in a wire die configuration may be
pressed into a sleeve (loose or tight fitting) prior to insertion into 8 carbide annulus.
20 By using sleeves, irregularities can be matched better, i.e. by using a less expensive,
easier to machine material for the sleeve. Sleeves may be made from material
including stainless steel, tungsten, cobalt or other desired materiaL It should be
understood that press-fitting the compact core into such a sleeve does not result in
the sleeve exerting any significant axial compression and only some non-uniform
25 radial compression on the press-fitted core. The polycrystalline core? with or
without a sleevet may fit into a carbide annulus somewhat loosely, leaving a slight
air gap therebetween. Such air gap may be filled with additional metal carbide or
other powder, if desired. The same is true with respect to a cylindrical or other
shapPd compact which is disposed upon a corresponding support. In this regard, it
30 should be understood that various interface materials may be placed between the
mating surfaces of the compact and the support. Such interface binders can be used
to affect (e.g. controV the degree of radial or axial compression. Suitable interface
materials include, for example, cobalt, nickel, tungsten, zirconium, tantalum,
molybdenum, manganese, or alloys such as, for example, cobalt/boron,
35 nickel/manganese, iron/nickel, cobalt/molybdenum/boron, nickel/manganese,
iron/nickel, cobalt/molybdenum/boron or the like or mixtures thereof. Such
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interfacial materials may be provided in powder form or may be pre-formed into an
annular sleeve for disposing around a diamond or CBN core intended for a wire die.
It is known that thermally stable compacts are recalcitrant to being bonded or
attached to supports due to gaseous/liquid/solid films which inhibit wetting of the
5 compact by the bonding agent being used to bond the compacts to the substrates.
Further, blocking of pores in the thermally stable compact by impurities prevents
penetration of the bonding agent into the core and reduces the strength of the bond.
Thus, i$ may be advantageous to utilize a reactive bonding mixture in order to
enhance the attachment or bonding of thermally stable compacts onto metal carbide
10 supports. The physical and/or chemical properties of the bonding agent, such as
cobalt, can be altered favorably by the addition of elements such as boron or
titanium. The addition of boron to cobalt reduces the melting point and yields amore reactive mixture with carbon. The boron in the mixture helps in wetting thedismond and forms cobalt-boron compounds, e.g. such as CollB2C. Addition to the
15 cobalt/boron mixture or other carbide formers incre~ses the reactivity further.
Other carbide formers which may be used include, for example, titanium, tantalum,
tungsten, niobium, molybdenum, and the like and mixtures thereof. In this regard, it
should be appreciated that other catalyst/solvent metals other than cobalt may be
used. Accordingly, suitable reactive bonding alloys include, for example, nickel/-
20 boron, cobalt/tantalum/boron, iron/nickel/boron, cobalt/boron, cobalt/boron/copper,cobalt/boron/tungsten, cobalt/boron/molybdenum, cobalt/niobium/boron, and the
like and mixtures thereof. It is thought, though unproven, that use of such reactive
bonding alloys, however, may eliminate compressive loading of the polycryst lline
compact by the substrate to which it is attached or bonded. For some uses,
2S however, such no~compressively loaded, supported polycrystalline cores may be quite advantageous, e.g. for subsequent bonding.
The following examples show how the present invention can be practiced, but
should not be construed as limiting. In this application, ~11 percentages and
proporffons are by weight unless otherwise expressly indicated.
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EXAMPLES
E XA I~PLE 1
A pre-sint~red diamond cylindrical core with an outside diameter (OD) nominal
dimension of 0.5 inches and a height of 0.5 inches was placed into a 16 vol-% cobalt
cemented tungsten carbide ring with dimensions of inside diameter tIDj 0.5 inches,
OD of 1.0 inches, and a height of 0.5 inches. The ring bearing the sintered core was
enclosed in a covered zirconium container and placed within a conventional HP/HTapparatus. Hot pressing of the sealecl container was conducted at 1200C at a
pressure of 50 Kbar for 15 minutes. Such conditions are within the stable range of
diamond with respect to pressure and temperature. First the temperature and thenthe pressurP were rem,oved from the cell and its contents removed upon cooling.
Such product had the visual appesrance of a conventionally prepared in situ bonded
polycrystalline diamond wire drawing die
EXAMPLE 2
The amount of core compression c~n be estimated by notching the bonded
support ring from the outer diameter toward the core using a wire EDM (elec!trical
discharge machining) apparatus. The notch is made perpendicular to the diamond
core;s tangent representing the shortest dist~nce between the carbide ring outside
diameter and the diamond core. The depth of the notch, measured from the outsidediameter inward to the point at which catas1rophic failure occurs, is a measure of
the amount of radial core compression which the ring exerts agaist the polyeystal-
line diamond core.
In this example, a polycrystalline diamond wire drawing die was made in
substantially an identical manner as that described in Example 1. The resulting die
had an overall OD of 0.950 inches, a carbide ring ID of 0.51 inches, and a thickness
of 0.45 inches. The carbide ring was made from 16 vol-% cobalt tungsten carbide.The EDP~ apparatus was equipped with a 0.010 inch diameter wire and was used to
notch the carbide as described above. A notch depth of 0.075 inches was requiredbefore catastrophic failure o~curred. Subsequent model calculations yielded a radial
core compression of 54 kpsi. These results demonstrate the compression which is
exerted by the carbide annulus on the polycrystalline diamond core of a diamond
wire drawing clie made in accordance with the present invention~
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EXAMPLE 3
Exerting a known pressure on the dismond core of a wire drawîng die made in
accordance with the present invention is a measure of the strength of the
attachment between the diamond core and the supporting carbide ring. In this type
S of test a rod with a diameter slightly sml~ller than the core diameter is used to apply
pressure to the core. A die blank made in accordance with the procedure of
Example 1 was made to have an OD of 0.950 inches, a carbide annulus ID of ~51
inches, and a thickness of 0.45 inches. This die blank wes placed in an Instron~est
machine such that a rod W8S pushillg only on the core. With a load of 17,560 pounds
(instrument maximum) on the rod, n~ push-out of the core was noted indicating that
the attachment of tha polycrystalline diamond core to the carbide ring indeed was
effective.
EXAMPLE 4
A pre-sintered thermally stable diamond cylindrical compact with an OD of
0.53 inches and a thickness of 0.05 inches was placed onto a cobalt cemented
tungsten carbide substrate (13 wt-96 cobalt) having dimensions of OD 0.56 inches and
a thickness of Q.15 inches. Various bonding agents were placed between the diamond
compact and the cemented tungsten carbide support. The bonding agents tested
were: (1) cobalt containing 5.19 weight percent boron; (2) cobait containing 22.3
weight percent tantalum and 4 18 weight percent boron; and (3) cobalt containing58.5 weight percent copper and 31.5 weight percent manganese. Bonding agent (2)
was tested at various thicknesses. The compact, bonding agent, and tungsten
carbide support were enclosed in a zirconium container and placed in a conventional
HP/HT apparatus. Attachment was accomplished at a temperature of oetween
about 1100 and 1?00C under a pressure of 50 Kbar for 10 minutes. It should be
noted that the top and bottom surfaces of the thermally st~ble diamond compacts
were lapped smooth and flat, the pieces cleaned, rinsed, dried, and fired in a
hydrogen atmosphere at 1,050C for one hour prior to attachment.
The supported thermally stable compacts removed from the HP/ElT apparatus
were ground to a diameter of 0.4995 i .0003 inches and the interface between thecompact and tungsten carbide clearly exposed. The tungsten carbide substrate wasplaced inside a supported circular holder made of tungsten carbide and having an ID
of 0.5000 ~ .0001 inches with only the attachment line and diamond table being
exposed. A second, unsupported holder was placed around the diamond table and
attachment line. The unsupported extension was then forced to shear. The amount
of force required to initiate shear is 8 measure of attachment strength. The data in
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the following table summarizes the strengths ~measured between the thermally
stable polycrystalline diamond compacts and the tungsten carbide supports.
Bonding Agent Bonding Agent She~r Stre~gth
No. Type Thickness (mils) (kn/cm
CO/13 1.8 9.1
2 C0/Ta/B 204 22.7
2 C0/Ta/B 4.8 19.6
2 ` C0/T~B 2.4 6.6
3 C0/CuJMn 2.0 18.9
The above-tabulated data shows that the thermally stable polycrystalline
diamond compscts were effectively attached to the tungsten carbide substrates.
15 The effe~t of shear strength on cutting performance has not yet been evaluated;
however, it is believed that higher shear strengths, above some minimum value, are
desirable. While not yet tested, it is believed that the presence of bonding agents is
not necessary for fabricating the supported thermally stable compacts of this
exampIe. Further, it is believed that the inventive process has application to
20 conventional diamond compacts also.
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