U.S. patent application number 14/368705 was filed with the patent office on 2014-12-04 for method of processing polycrystalline diamond material.
The applicant listed for this patent is Element Six Abrasives S.A.. Invention is credited to Andrew Ndlovu, Humphrey Samkelo Lungisani Sithebe.
Application Number | 20140352228 14/368705 |
Document ID | / |
Family ID | 45695062 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140352228 |
Kind Code |
A1 |
Sithebe; Humphrey Samkelo Lungisani
; et al. |
December 4, 2014 |
METHOD OF PROCESSING POLYCRYSTALLINE DIAMOND MATERIAL
Abstract
A method of processing a polycrystalline diamond (PCD) material
having a non-diamond phase comprising a diamond catalyst/solvent
material comprises leaching an amount of the diamond
catalyst/solvent from the PCD material by exposing at least a
portion of the PCD material to a leaching mixture. The leaching
mixture comprises hydrochloric acid and one or more additional
mineral acids, the molar concentration of the hydrochloric acid
being greater than the molar concentration of the one or more
additional mineral acids in the leaching mixture.
Inventors: |
Sithebe; Humphrey Samkelo
Lungisani; (Springs, ZA) ; Ndlovu; Andrew;
(Springs, ZA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
|
LU |
|
|
Family ID: |
45695062 |
Appl. No.: |
14/368705 |
Filed: |
December 20, 2012 |
PCT Filed: |
December 20, 2012 |
PCT NO: |
PCT/EP2012/076520 |
371 Date: |
June 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61581214 |
Dec 29, 2011 |
|
|
|
Current U.S.
Class: |
51/309 ;
51/307 |
Current CPC
Class: |
C04B 35/52 20130101;
B24D 99/00 20130101; C04B 2235/427 20130101 |
Class at
Publication: |
51/309 ;
51/307 |
International
Class: |
B24D 99/00 20060101
B24D099/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 29, 2011 |
GB |
1122434.2 |
Claims
1. A method of processing a polycrystalline diamond (PCD) material
having a non-diamond phase comprising a diamond catalyst/solvent
material, the method comprising leaching an amount of the diamond
catalyst/solvent from the PCD material by exposing at least a
portion of the PCD material to a leaching mixture, the leaching
mixture comprising hydrochloric acid and one or more additional
mineral acids, the molar concentration of the hydrochloric acid
being greater than the molar concentration of the one or more
additional mineral acids in the leaching mixture.
2. The method of claim 1, wherein the step of exposing the PCD to a
leaching mixture comprises exposing the PCD to the leaching mixture
wherein the one or more additional mineral acids comprise one or
more of sulphuric acid, phosphoric acid, perchloric acid, or nitric
acid.
3. The method of claim 1, wherein the leaching solution comprises
hydrochloric acid at a molar concentration of around 3M or
greater.
4. The method of claim 1, wherein the leaching mixture comprises a
combination of two or more mineral acids in addition to
hydrochloric acid, the molar concentrations of the two or more
additional mineral acids being substantially identical.
5. The method of claim 1, further comprising heating the leaching
mixture to a temperature equal to or greater than the boiling
temperature of the leaching mixture during the step of exposing the
PCD material to the leaching mixture.
6. The method of claim 1, wherein the metal-solvent catalyst
comprises at least one of: cobalt; nickel; iron.
7. The method according to claim 1, wherein the PCD table has a
thickness of from about 1.5 mm to about 3.0 mm.
8. The method of claim 1, wherein the step of leaching comprises
leaching one or more of a carbide of tungsten, titanium, niobium,
tantalum, zirconium, molybdenum, chromium, or vanadium from the PCD
material.
9. The method of claim 1, wherein for an average diamond grain size
of around 10 microns, the rate of leaching by the acid leaching
mixture is around 10 microns per hour.
10. (canceled)
Description
FIELD
[0001] This disclosure relates to a method of processing a body of
polycrystalline diamond (PCD) material and to a mixture for said
processing.
BACKGROUND
[0002] Cutter inserts for machining and other tools may comprise a
layer of polycrystalline diamond (PCD) bonded to a cemented carbide
substrate. PCD is an example of a superhard material, also called
superabrasive material, which has a hardness value substantially
greater than that of cemented tungsten carbide.
[0003] Components comprising PCD are used in a wide variety of
tools for cutting, machining, drilling or degrading hard or
abrasive materials such as rock, metal, ceramics, composites and
wood-containing materials. PCD comprises a mass of substantially
inter-grown diamond grains forming a skeletal mass, which defines
interstices between the diamond grains. PCD material comprises at
least about 80 volume % of diamond and may be made by subjecting an
aggregated mass of diamond grains to an ultra-high pressure of
greater than about 5 GPa, typically about 5.5 GPa, and temperature
of at least about 1200.degree. C., typically about 1440.degree. C.,
in the presence of a sintering aid, also referred to as a catalyst
material for diamond. Catalyst material for diamond is understood
to be material that is capable of promoting direct inter-growth of
diamond grains at a pressure and temperature condition at which
diamond is thermodynamically more stable than graphite.
[0004] Examples of catalyst materials for diamond are cobalt, iron,
nickel and certain alloys including alloys of any of these
elements. PCD may be formed on a cobalt-cemented tungsten carbide
substrate, which may provide a source of cobalt catalyst material
for the PCD. During sintering of the body of PCD material, a
constituent of the cemented-carbide substrate, such as cobalt from
a cobalt-cemented tungsten carbide substrate, liquefies and sweeps
from a region adjacent the volume of diamond particles into
interstitial regions between the diamond particles. In this
example, the cobalt acts as a catalyst to facilitate the formation
of bonded diamond grains. Optionally, a metal-solvent catalyst may
be mixed with diamond particles prior to subjecting the diamond
particles and substrate to the HPHT process. The interstices within
PCD material may at least partly be filled with the catalyst
material. The intergrown diamond structure therefore comprises
original diamond grains as well as a newly precipitated or re-grown
diamond phase, which bridges the original grains. In the final
sintered structure, catalyst/solvent material generally remains
present within at least some of the interstices that exist between
the sintered diamond grains.
[0005] The sintered PCD has sufficient wear resistance and hardness
for use in aggressive wear, cutting and drilling applications.
[0006] A well-known problem experienced with this type of PCD
compact, however, is that the residual presence of solvent/catalyst
material in the microstructural interstices has a detrimental
effect on the performance of the compact at high temperatures as it
is believed that the presence of the solvent/catalyst in the
diamond table reduces the thermal stability of the diamond table at
these elevated temperatures. For example, the difference in thermal
expansion coefficient between the diamond grains and the
solvent/catalyst is believed to lead to chipping or cracking in the
PCD table of a cutting element during drilling or cutting
operations. The chipping or cracking in the PCD table may degrade
the mechanical properties of the cutting element or lead to failure
of the cutting element. Additionally, at high temperatures, diamond
grains may undergo a chemical breakdown or back-conversion with the
solvent/catalyst. At extremely high temperatures, portions of
diamond grains may transform to carbon monoxide, carbon dioxide,
graphite, or combinations thereof, thereby degrading the mechanical
properties of the PCD material.
[0007] A potential solution to these problems is to remove the
catalyst/solvent or binder phase from the PCD material.
[0008] Chemical leaching is often used to remove metal-solvent
catalysts, such as cobalt, from interstitial regions of a body of
PCD material, such as from regions adjacent to the working surfaces
of the PCD. Conventional chemical leaching techniques often involve
the use of highly concentrated, toxic, and/or corrosive solutions,
such as aqua regia and mixtures including hydrofluoric acid (HF),
to dissolve and remove metallic-solvent/catalysts from
polycrystalline diamond materials. As such mixtures are highly
toxic, the use of these carry severe health and safety risks and
therefore processes for treating PCD with such mixtures must be
carried out by specialised personnel under well-controlled and
monitored conditions to minimise the risk of injury to the
operators of such processes.
[0009] Furthermore, it is typically extremely difficult and time
consuming to remove effectively the bulk of a metallic
catalyst/solvent from a PCD table, particularly from the thicker
PCD tables required by current applications. In general, the
current art is focussed on achieving PCD of high diamond density
and commensurately PCD that has an extremely fine distribution of
metal catalyst/solvent pools. This fine network resists penetration
by the leaching agents, such that residual catalyst/solvent often
remains behind in the leached compact. Furthermore, achieving
appreciable leaching depths can take so long as to be commercially
unfeasible or require undesirable interventions such as extreme
acid treatment or physical drilling of the PCD tables.
[0010] There is therefore a need to overcome or substantially
ameliorate the above-mentioned problems through a technique for
treating or processing a body of PCD material.
SUMMARY
[0011] Viewed from a first aspect there is provided a method of
processing a polycrystalline diamond (PCD) material having a
non-diamond phase comprising a diamond catalyst/solvent material,
the method comprising leaching an amount of the diamond
catalyst/solvent from the PCD material by exposing at least a
portion of the PCD material to a leaching mixture, the leaching
mixture comprising hydrochloric acid and one or more additional
mineral acids, the molar concentration of the hydrochloric acid
being greater than the molar concentration of the one or more
additional mineral acids in the leaching mixture.
[0012] The leaching mixture may comprise, for example, one or more
mineral acids comprising one or more of sulphuric acid, phosphoric
acid, perchloric acid, or nitric acid.
[0013] In some embodiments, the molar concentration of the
hydrochloric acid is 3M or greater.
[0014] In some embodiments, the leaching solution comprises a
combination of two or more mineral acids in addition to
hydrochloric acid, the molar concentrations of the two or more
mineral acids being substantially identical.
[0015] The method may further comprise heating the leaching
solution to a temperature equal to or greater than the boiling
temperature of the leaching mixture during the step of exposing the
PCD material to the leaching mixture.
[0016] For an average diamond grain size of around 10 microns, the
rate of leaching by the acid mixture may, in some embodiments be
around 10 microns per hour.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Various embodiments will now be described in more detail, by
way of example only, with reference to the accompanying figures in
which:
[0018] FIG. 1 is a schematic perspective view of a PCD cutter
insert for a cutting drill bit for boring into the earth; and
[0019] FIG. 2 is a schematic cross section view of the PCD cutter
insert of FIG. 1 together with a schematic expanded view showing
the microstructure of the PCD material;
[0020] The same reference numbers refer to the same respective
features in all drawings.
DETAILED DESCRIPTION OF EMBODIMENTS
[0021] As used herein, "PCD material" is a material that comprises
a mass of diamond grains, a substantial portion of which are
directly inter-bonded with each other and in which the content of
diamond is at least about 80 volume % of the material. In one
embodiment of PCD material, interstices among the diamond gains may
be at least partly filled with a binder material comprising a
catalyst for diamond and/or a non-diamond phase.
[0022] As used herein, "catalyst material for diamond" is a
material that is capable of promoting the growth of diamond or the
direct diamond-to-diamond inter-growth between diamond grains at a
pressure and temperature at which diamond is thermodynamically more
stable than diamond.
[0023] The term "molar concentration" as used herein, may refer to
a concentration in units of mol/L at a temperature of approximately
25[deg.] C. For example, a solution comprising solute A at a molar
concentration of 1 M may comprise 1 mol of solute A per litre of
solution.
[0024] FIG. 1 shows a PCD cutter insert 10 for a drill bit (not
shown) for boring into the earth, comprising a PCD body 20 bonded
to a cemented tungsten carbide substrate 30.
[0025] FIG. 2 is a cross-section through the PCD cutter insert 10
of FIG. 1. The microstructure 21 of the PCD body 20 is also shown
and comprises a skeletal mass of inter-bonded diamond grains 22
defining interstices 24 between the diamond grains, the interstices
24 being at least partly filled with a filler material, namely a
solvent/catalyst for diamond comprising, for example, cobalt,
nickel or iron.
[0026] In accordance with some embodiments of the method, a
sintered body of PCD material is created having diamond to diamond
bonding and having a second phase comprising solvent/catalyst
dispersed through its microstructure together. The body of PCD
material may be formed according to standard methods, using HpHT
conditions to produce a sintered PCD table. The PCD tables to be
leached by embodiments of the method typically, but not
exclusively, have a thickness of about 1.5 mm to about 3.0 mm.
[0027] It has been found that the removal of non-binder phase from
within the PCD table, conventionally referred to as leaching, is
desirable in various applications, for example, where it is desired
to reattach the polycrystalline diamond disk to a carbide post,
which is typically accompanied by re-infiltration of, for example,
a binder material in order for such re-attachment to be successful.
The carbide grains can potentially block the pathways along which
re-infiltration occurs. These blockages prevent the complete
re-infiltration of the binder material during the reattachment
cycle, which in turn has deleterious consequences for the
reattachment process.
[0028] Also, the residual presence of solvent/catalyst material in
the microstructural interstices is believed to have a detrimental
effect on the performance of PCD compacts at high temperatures as
it is believed that the presence of the solvent/catalyst in the
diamond table reduces the thermal stability of the diamond table at
these elevated temperatures.
[0029] The reaction rate regarding leaching is considered to be
dominated by the chemical rate initially as acid contacts a surface
of the PCD table and later by the diffusion rate as the acid
diffuses through the pores of the PCD table.
[0030] Conventionally, HF--HNO.sub.3 has been shown to be the most
effective media for the removal of tungsten carbide (WC) from the
sintered PCD table. The problem with HF--HNO.sub.3 is that it is
volatile and, when heating this acid, specific technology, for
example, gas sealing technology, is required. If such technology is
not provided then the application of temperature will reduce the
efficacy of HF--HNO.sub.3 due to evaporation of the HF (which is
poisonous) and formation of NO species, which are usually gaseous,
and thus frequent replenishment of the acid media is required.
Furthermore, as outlined above heat would ordinarily be required to
accelerate the leaching process in order to render the process
commercially feasible. Another problem is that HF--HNO.sub.3 is
corrosive to most containment vessels making the reaction difficult
to perform.
[0031] To improve the performance and heat resistance of a surface
of the body of PCD material 20, at least a portion of the
metal-solvent catalyst, such as cobalt, may be removed from the
interstices 22 of at least a portion of the PCD material 20.
Additionally, tungsten and/or tungsten carbide may be removed from
at least a portion of the body of PCD material 20.
[0032] Chemical leaching is used to remove the metal-solvent
catalyst from the body of PCD material 20 either up to a desired
depth from an external surface of the body of PCD material or from
substantially all of the PCD material 20. Following leaching, the
body of PCD material 20 may therefore comprise a first volume that
is substantially free of a metal-solvent catalyst. However, small
amounts of solvent/catalyst may remain within interstices that are
inaccessible to the leaching process. Additionally, following
leaching, the body of PCD material 20 may also comprise a volume
that contains a metal-solvent catalyst. In some embodiments, this
further volume may be remote from one or more exposed surfaces of
the body of PCD material 20.
[0033] The interstitial material which may include, for example,
the metal-solvent/catalyst and one or more additions in the form of
carbide additions, may be leached from the interstices 22 in the
body of PCD material 20 by exposing the PCD material to a suitable
leaching mixture.
[0034] According to embodiments, the leaching mixture comprises one
or more mineral acids in addition to hydrochloric acid, wherein the
molar concentration of the hydrochloric acid present in the
leaching mixture is greater than the molar concentration(s) of the
other mineral acid(s) in the mixture. The body of PCD material may
be exposed to such a leaching mixture in any suitable manner,
including, for example, by immersing at least a portion of the body
of PCD material 20 in the leaching mixture for a period of
time.
[0035] According to some embodiments, the body of PCD material may
be exposed to the leaching mixture at an elevated temperature, for
example to a temperature at which the acid leaching mixture is
boiling. Exposing the body of PCD material to an elevated
temperature during leaching may increase the depth to which the PCD
material may be leached and reduce the leaching time necessary to
reach the desired leach depth.
[0036] If only a portion of the body of PCD material is to be
leached, the body, and if it is still attached to the substrate,
the substrate may be at least partially surrounded by a protective
layer to prevent the leaching solution from chemically damaging
certain portions of the body of PCD material and/or the substrate
attached thereto during leaching. Such a configuration may provide
selective leaching of the body of PCD material, which may be
beneficial. Following leaching, the protective layer or mask may be
removed.
[0037] Additionally, in some embodiments, at least a portion of the
body of PCD material and the leaching solution may be exposed to at
least one of an electric current, microwave radiation, and/or
ultrasonic energy to increase the rate at which the body of PCD
material is leached.
[0038] Examples of suitable mineral acids may include, for example,
sulphuric acid, phosphoric acid, perchloric acid or nitric acid
and/or any combination of the foregoing or other mineral acids.
[0039] In some embodiments, hydrochloric acid may be present in the
leaching mixture in an amount of around 3 M or greater than around
3 M.
[0040] Some embodiments are described in more detail with reference
to the following examples which are not intended to be limiting.
The following examples provide further detail in connection with
the embodiments described above.
Example 1
[0041] Cutting elements, each comprising a PCD table attached to a
tungsten carbide substrate, were formed by HPHT sintering of
diamond particles in the presence of cobalt. The
sintered-polycrystalline-diamond tables included cobalt within the
interstitial regions between the bonded diamond grains.
[0042] The PCD table was leached using a solution comprising
hydrochloric acid, nitric acid, phosphoric acid and sulphuric acid
with a total molar concentration of the leaching mixture being 4.60
M, the nitric acid, phosphoric acid and sulphuric acid being
present in the leaching mixture at equal Molar concentrations and
the hydrochloric acid being present in a greater Molar
concentration than any of the other mineral acids, for example,
around 3M.
[0043] The PCD table was leached for 15 hours at a temperature at
which the acid leaching mixture was boiling.
[0044] At this time the leached depth of the PCD table was
determined for various portions of the PCD table, through x-ray
analysis. It was found that an average leach depth of 270 microns
had been achieved after 15 hours.
[0045] Another identical body of PCD material was leached for a
total 25 hours using this leaching mixture and the leached depth of
the PCD table was again determined for various portions of the PCD
table using x-ray analysis. It was found that an average leach
depth of 450 microns had been achieved after 25 hours.
Example 2
[0046] Cutting elements, each comprising a PCD table attached to a
tungsten carbide substrate, were formed by HPHT sintering of
diamond particles in the presence of cobalt. The
sintered-polycrystalline-diamond tables included cobalt within the
interstitial regions between the bonded diamond grains.
[0047] The PCD table was leached using a solution comprising
hydrochloric acid, nitric acid, phosphoric acid and sulphuric acid
with a total molar concentration of the leaching mixture being 4.87
M, the nitric acid, phosphoric acid, perchloric acid and sulphuric
acid being present in the leaching mixture at equal Molar
concentrations and the hydrochloric acid being present in a greater
Molar concentration than any of the other mineral acids, for
example, around 3M.
[0048] The PCD table was leached for 10 hours at a temperature at
which the acid leaching mixture was boiling.
[0049] At this time the leached depth of the PCD table was
determined for various portions of the PCD table, through x-ray
analysis. It was found that an average leach depth of 250 microns
had been achieved after 10 hours.
[0050] Another identical body of PCD material was leached for a
total 33 hours using this leaching mixture and the leached depth of
the PCD table was again determined for various portions of the PCD
table, through x-ray analysis. It was found that an average leach
depth of 600 microns had been achieved after 33 hours.
[0051] When compared with the leach depths achievable using
conventional leaching solutions, it has been determined that the
embodiments including the above leaching mixtures may enable a
greater leaching efficiency to be achieved with greater leach
depths being achievable in a shorter period of time for example, a
leach depth of 585 microns was achieved in 20 hours compared to a
conventional acid mixture which is capable of leaching an identical
body of PCD in typically 5 days. Furthermore, health and safety
handling issues are reduced as the acid leaching mixture is less
toxic than other conventional HF-nitric based leaching
mixtures.
[0052] The preceding description has been provided to enable others
skilled the art to best utilize various aspects of the embodiments
described by way of example herein. This description is not
intended to be exhaustive or to be limited to any precise form
disclosed. Many modifications and variations are possible. In
particular, whilst some embodiments of the method have been
described as being effective in leaching PCD containing VC
additives, the method may be equally applicable to the effective
leaching of PCD with other additives such as those in the form of
other metal carbides including one or more of a carbide of
tungsten, titanium, niobium, tantalum, zirconium, molybdenum, or
chromium.
* * * * *