Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a method for the
preparation of fuIly dense, consolidated diamond or
diamond composite articles as ~or use in cutting and
drilling appIications. The invention involves heat
treating the article to improve wear and fracture
resistance.
Desc~iption of the Prior Art
The conYentional synthesis of diamond grit or
powder involve5 the conversion of a non-diamond carbon
to diamond in the presence of a metal acting as a
solvent-catalyst under conditions of high temperature
and high pressure at which diamond is the
thermodynamically stable form o~ carbon. Although
various carbonaceous materials, such as charcoal, coal,
coke and graphite may be used a~ the carbon source,
typically graphite, and specifically spectrally pure
graphite, is used almos~ exclusively for the ~ommercial
production of diamond grit or powder~ It is also
p~s~ible to us~ as the carbon source carbon-containing
organic compounds, such as anthracene, fluorene,
pyrene, sucrose, camphor and the like.
With the use o~ graphite as the carbon source
in accordance with the preferrQd practice, the graphite
may be a powder, a disc o~ compxessed an~ machined
powder or a cap~ule into which the graphite is placed
with the solvent-catalyst. Typically, the graphite
charge in one o~ the above for~s is converted to
diamond in the presence of one or more metals or
metal-containing compounds serring as the
solvent-catalyst. Graphite can be converted directly
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to diamond in the absence of a catalyst but pressures
of about 130 kbar and temperatures in the range of 3000
to 4000C are required. With the addition of
conventional solvent-catalysts lower pressures and
temperatures may be used in the range of 1200 to 1600C
and 50 to 80 kbar, respectively. The solvent catalyst
dissolves the graphite until a saturated solution of
carbon relative to graphite is obtained. The catalytic
effect is the promotion o~ the structural rearrangement
of the graphite to diamond. Significant
solvent catalysts are the Group VIII ~ransitio~ metals,
including platinum, chromium, tantalum, manganese and
alloys containing at least one of these metals. Iron,-
nicXel, cobalt and manganese are the preferred pure
metal solvent-catalysts and iron-manganese,
nickel-chromium, nickel-manganese, iron-nickel,
nickel-cobalt and various other nickel-containing
alloys are generally the preferred alloys for this
purpose. The solvent-catalyst is employed either in
powder form, which may be loose or compacted, or in the
form of a disc.
Other additives, such a~ boron, are sometimes
used as additions to the charge to be compacted in
order to change one or more of the properties o~ the
resultant diamond consolidated article. The
solvont-catalyst to carbon volume ratios are typically
0.1 to 10 with a preferred ratio o~ 0.5 to 2.
Consolidation is achieved typically by the use of belt
presses or cubic presses. The constituents are loaded
into a cell of cylindrical configuration. Heating is
usually provided by passing an elactric current
directly through ~he charge within the cell.
The graphite-to-diamond conversion is
performed in the diamond stable region of temperatures
and pressures in the range of ~200 to 2500C and 50 to
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120 kb~r, respectively. The reaction time is usually
within the ranye o~ 0.5 to 20 minutes.
Broadly, the consolidation sequence includes
pressurization, heating to desired maximum reaction
temperature, reaction time to permit conversion,
cooling down and pressur~ release.
After cooling of the consolidated charge or
mass, the diamond crystals are separated ~rom the metal
matrix by acid dissolution. ~or ~his purpos~, ni~ric
acid may be used at a temperature of 100 to 300C,
which dissolves all of the constituents except the
diamonds. The diamonds may ~hen be separated ~rom the
liquid by centrifuge or ~iltration. IP, after this
dissolution step, the diamonds are agglomerated, they
may be separated by a light-crushing operation. The
separated diamonds may then be sorted according to size
and shape. The size of the resulting diamond grit or
powder may vary within the range of 1 micron up to
about lmm.
Diamond particles so produced may be
compacted into a substantially Pully dense consolidated
article, such as drill blanks ~or use in producing
drill bits. For this purpose, the charge may be
compacted to produce a monolithic ~tructure or may be
compacted onto a disc or substrate of or example
tungs~en carbidQ and cobalt. The resulting disc o~ the
substrate with a diamond layer thereon may be assembled
in various configurations depending upon the cutting or
drilling device with which it is assembled, In any
event, consolidation is achieved by ~intering the
diamond powder at high temperatures and high pressures
in the diamond stable region in the presence of a
ca~alyst or a non-catalytic sintering aid to obtain a
strong, int~rbonded, polycrystalline consolidated mass
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or article o~ substantially full density. The
apparatus used ~or compacting may be the same as used
in the synthesis of the diamond particles. Cell
assemblies typically used in these applications ars
described in U.S. Patent 3,407,4S5 and U.S. Patent
4,604,106.
According to prior-art compacting or
consolidating practice, including the U.S. patents
listed hereafter, the preferred charge is diamond
powder although graphite powder may be mixed therewith.
In tbi~ application, the diamond powder generally
constitutes at least 70 volume % of the total mass,
preferably 90 to 99%. The final compacted article has
diamond grainæ of 10 to 20 microns but depending upon
the temperature may have a large-grain structure of
about 100 microns.
Prior to charging of the diamond powder to
cell, the diamond powder may be cleaned by heating it
in the presence o~ hydrogen gas typically for one hour
at a temperature within the range o~ 800 to 1000C.
Boron may be employed as a sintering aid for the
diamond powder and is typically introduced by doping
the diamond powder prior to introducing the diamond
charge to the cell ~or compactinq. Also, a
pretreatment step involving sur~ace graphitization o~
the diamond powder may be per~ormed to provide thereon
a uniform coating of graphite which promotes the
p~netration o~ the catalyst into the diamond layer
within the cell by continuously dissolving ~he graphite
to form diamond during high tempera~ure compacting.
The catalyst-carbide charge may consis~ o~ cobalt,
nickel or iron catalyst powder mixed with tungst2n
carbide, titanium carbide or tantalum carbide powder.
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The following table lists patents
representative of conventional practices relating to
consolidated diamond or diamond composite articles:
Patent Issue Date Summary
U.S. 3,141,746 7/21/64 Diamond compact abrasive
by sintering a mixture of
diamond powder (50~ vol%)
with a catalytic metal
: powder (one or more of
Fe, Ni, C~ and Ti) in the
diamond stable region.
U.S. 3,574,S30 4/13/71 A method of making
interbonded diamond
compacts by sintering
clean diamond powder in
the diamond stable
region, optionally
intermixed with up to 3
wt% B, Si, or Be powder
as a sinteri.ng aid.
U.S. 3,745,623 7/17/73 Relates to powder diamond
compact blanks having a
70~ vol% interbonded
diamond layer joined to a
cemented carbide
substr te and the method
for making them.
.S. 4,224,380 9j23/80 A temperature-resistant,
leached powder diamond
compact formed by the
removal of the metallic
catalyst phase form the
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interbonded diamond.
U.S. 4,28~,248 9/8/81 A method of making the
temperature-re istant,
leached powder diamond
material and compacts of
U.S. 4,224,380 by acid
leaching.
U.S. 4,518,659 5/21/85 An improved process ~or
making powder diamond
compacts using a first
catalyst (copper) to
sweep through the diamond
charge preceding a Co
catalyst.
U.S. 4,592,433 6/3/86 A powder diamond compact
blank of diamond strips
in a grooved cemented
carbide substrate.
As described in U.S. Patent 3,7~5,623, the
cell assembly for consolidation may include a salt
5pacer, a zirconium disc separator, a tungsten
carbide/cobalt disc, a diamond powder layer and an
additlonal zirconium di~c separator. The loading
se~u~nce involves the s~acking of several single
c~arges of this constructlon in a zirconium or tantalum
metal sheath or capsule which is placed in the cell
after the capsule is fu}l.
The steps involved in consolidation are
similar to the processing ~or synthesis of ~he diamond
powder. Namely, the process includes prsssurization
from G.001 to 50 kbar or greater and heating up to
sintering temperature from 20 to 1500C or greatex.
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Sintering may be effected at a pressure of 50 kbar and
a temperature of 1500C for 10 minutes. Cooling down
is then effected from a temperature of 1500~C to a
temperature of 20C or less with pressure release from
50 to less than 0.001 kbar. Sintering is generally
conducted within the temperature range of 1200 to
1500C and the pressure range of 40 to 70 kbar.
Sinterin~ times are generally within the ranye of 10 to
15 minutes, particularly when a belt preæs is ~mployed,
with sintering times less than 3 minutes being possible
with the use of a cubic press.
After consolidation, the stack of sintered,
consolidated blanks is separated manually and the
z~rconium capsule is removed. Lapping and polishing
operations are employed to remove any particles o~
material adhering to the edges and flat surfaces of the
blanks. The blanks are then ground to shape, which is
typically cylindrical, and to the dimensions required
~or the particular cutting or drilling assembly with
which they are to be used. Sizes conventionally
employed for this purpose are diameters of about 1 to
5.5 c~ with thicknesses of 3.5 to 8 mm, which includes
a 0.7 to 1 mm thick diamond layer on the blank
assembly. The resulting product is a di~c of two layer
structure, specifically a substrate of a composition,
such as tungsten carbide and cobalt, with a fully dense
layer o~ diamond particles bonded thareto.
Further post-consolidation acid leaching
treatments involving nitric and hydrochloric acid have
also b~en used for fabricating temperature-resistant
powd~r diamond ma~erial and compacts, from which most
of the interp~netrating network of Co has been removed.
This prior art is described in U.S. Patent 4,224,380
and U.S. Patent 4,288,248.
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For spe~ific appllcations such as the
production of drill bits used ln oil well dril~-ng
applications, the disc is mounted on a cutter by che
use of a brazing step. Specifically, the blank is
braxed onto a tungsten carbide/cobalt post. A
plurality of these post-disc assemblies are then
mounted on drill bits of various configurations with
the diamond portion of each acting as a cutting
surface. Multiple cuttars of leached powder diamond
material may also be brazed into the sur~ace of
matrix-body drill bits, replacing either some or all of
natural diamond stones t~pically used in such bits.
Drill bits of these types constructions are well known
in the art.
During use of the above-described
consolidated diamond articles for cutting and drilliny
applications, it is advantageous that these articles be
characterized by high wear resistance and resistance to
cracking. Applicants have determined, in this regard,
that during the high temperature compacting operation
to achieve the fully dense, consolidated diamond
article, dislocations in the diamond crystal structure
result. Dislocations in crystalline materials, such as
diamond, are linear regions of lat~ice imperfection~
These imper~ections allow the crystal to underyo
plastic deformation at sufficiently high temperatures
and are also generated by the deformation process.
Since these imperfections consist of regions of lattice
distortion, they generate highly loralized stress
fields. As such, they provide sites for crack
initiation and propagation when the diamond article is
under high applied stress characteristic of use thereof
in cutting and drilling applications. Likewi e, these
dislocations in the diamond crystal structure adversely
affect the wear resistance of the consolidated diamond
arcticle during use thereof in cutting or drilling
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applications by providing sites for ~racture or
chipping away o.~ the article at regions of stress
difference caused by these dislocations resultinq
during the high temperatur~ compacting of diamond
particles to form a consolidated article therefrom
adversely affect the performance of the article from
the standpoints of both cracking, which in severe
instances may rPsult in catastrophic failure, and wear
resistance.
ummary of the Invention
It is accordingly a primary object of the
present invention to provide a method for fabricating a
substantially fully dense diamond or diamond composite
article, wherein the production of dislocations in the
crystal structure adversely affecting resistance to
cracking and promoting wear is diminished..
A more specific object of the invention is to
provide a method for consolidating diamond particles
wherein a heat~txeating step i~ employed to rearrange
and remove dislocation~ in the crystal structure to
achieve therein substantially strain-freQ diamond
gralns .
An additional ob;ect of the invention is to
provide a heating step in the compac~ing o~ diamond
powders ~o produce a subs~antially skrain free state or
racovered state in the microstructure of the
consolidated article, and in addition pro~ide for
control of the perfection of the crystal structure
thereof.
Yet a further object o~ the invention is to
provide an improved leaching step ~or extracting
substantially all the cobalt from the strain-free
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compact, thereby further improving its thermal
stability.
Additional objects and advantages of the
present invention will be set forth in part in the
description that follows and in part will be apparent
from the description or may be learned by the practice
of the invention. The objects and advantages of the
invention may be realized and obtained by the method
particularly pointed out in the appended claim~.
In accordance with th~ me~hod o~ the
invention, con olidation of finely divided diamond
particles is achieved to produce a substantially fully
dense article. The method comprises heating a charge
including finely divided diamond particles to an
elevated, compacting temperature and in compacting the
charge, while at this elevated temperature! to form the
desired substantially fully dense ~rticle therefrom.
Thereafter, in accordance with the invention, the
article is held at an elevated temperature and time
~ufficient to rearrange and remove substantially all
the dislocations in the article resulting during the
aforementioned compacting. This achieves, in the
article, a substantially strain-free state. The
article i~ finally cooled to room temperature.
Further, in accordance with the invention,
the atep o~ holding the article at elevaked tamperature
may comprise maintaining the article at an elavated
temperature af~er compac~ing and prior to cooling to
room temperature from the elevated compacting
temperature. The elevated temperature at which the
article is maintained may be lower than the compacting
temperature but still sufficient to rearrange and
remove said dislocations. Alternately, in accordance
with the inven~ion, the step of holding the ar~icle at
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elevated temperature may comprise cooling the article
from the elevated compacting temperature and then
reheating the article to said sufficient elevated
temperature for a time sufficient to rearrange and
substantially remove any di~locations in the article
resulting during compacting ~o achieve a substantially
strain-free state in the articlP. The reheating may be
to an elevated te~perature sufficient to achieve
diamond cxystal growth or may be below the diamond
crystal growth temperature.
Further, in accordance with the invention,
prior to cooling the article to room temperature, the-
article may be heated to a higher temperature and
cooled from this higher temperature at a controlled
cooling rate sufficient to rearrange and substantially
remove any dislocations in the article resulting during
compacting to achieve a substantially strain-free
state. This heating ~tep may be at a te~p rature
sufficient to achieve diamond crystal growth or at a
temperature at which substantial diamond crystal growth
do~s no~ result. As an alternate practice in
accordance with the invention, acid leaching may be
performed on the article a~ter compactiny to remove
ther~from any metal employ~d during syn~hesis of the
article. The leachant may be nitric acid, a
combination o~ nitric acid ~nd hydrochloric ~cid, or
hydrogen peroxide. The metal ~mployed during a
synthesis of the article may be iron, cobalt, or
nickel.
~ he holding of the diamond compact at
elevated temperature for purposes og rearranging and
removing a substantial portion of the dislocations
therein to achieve a substantially strain-free state in
accordance with the practice o~ the invention may be at
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an elevated temperature within the range o~ 1200 ~o
2000C for 13 ~o 125 minutes.
Typically, in accordance with the practice of
the invention, the finely divided diamond particles
used for producing the consolidated article are within
the particle size range of 1 to 200 microns.
Detailed Dascription o~ the Preferred Embodiments
Reference will now be made in detail to
presently preferred embodiments of the invention,
examples of which are described below.
In the experimental work resulting in the
inv~ntion, applicants have examined conventional
diamond particle consolidated articles subjected to
wear incident to typical cutting and drilling
applications. The wear and fracture characteristics of
tha particles examined indicated that wear thereof
results ~rom chipping away at dislocations and that
these di~location~ also provide sites for crack
propagation under applied working stress which may
result in catastrophic failure of the articles. By
heat treating the articles in accordance with
applicants' invention, applîcants have provided for
4rearranging and removing these dislocations to achieve
a ~ubstantia}ly strain-free state in the article. In
this man~er, both wear resistance and resistance to
cracking is improved.
Tha following constitutes typical examples of
the prac~ice of the inventionO
Exam~le l
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A diamond particle charge produced in
accordance with the aforementioned conventional
practice is placed atop a tungsten carbide-cobalt
substrate, with a salt and zirconium spacer, within a
~irconium tube, which i~ then sealed with zirconium
discs on both ends. Thi~ capsule structure is in
accordance with the structure and practice described in
U.S. Patents 3,745,623 and 4,604,106.
The capsule is heated to a temperature of
1550~ during which time pressure is applied by the use
of a belt press constructed and operated in accordance
with the disclosure in U.5. Patent 3,407,455. The
sample is maintained for 10 minutes at a temperature
and pressure of 1550C and 60 kbar, respectively, to
achieve a. substantially fully dense article.
Thereafter, the article i~ held at a te~peratur~ of
1550C ~or 60 minutes prior to cooling to room
temperature. This heating step results in rearranging
and removing a substantial portion of the dislocations
in the article resulting during th~ high temperature
compacting to achieve therein a substantially
strain-free state.
Example ~
The practice of Example 1 is rep~ated except
that the axticle is heated to a higher temperature
after consolidation, which temperature is 1700~C, and
control coolPd ~rom this tQmperature over a period of
about 15 minutes to room temperature, whereby
rearranging and removing of dislocations in the article
resulting during compacting is obtained to achieve a
substantially strain-~ree state.
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~xam~le 3
The cycle of Example l is repeated except
that after compacting, the article is cooled from the
compacting temperature ts 1300C and then reheated to
an elevated temperature of l700aC for 45 minutes to
substantially reduce the n~mber of disloc tions in the
article r~sulting during compactinq to achieve a
substantial1y strain-fxee state.
E~ample 4
Improved acid leaching o~ the compacts
produced in accordance with the foregoing examples was
performed ueing the following practices, which result
in a cobalt-free leached diamond composite free of
cobalt impurity,t hereby resulting in better
temperature resistance of the leached compact.
The diamond compact lay~r was first removed
from the tungsten carbide-co~alt substrate by electric
discharge machining. The resulting diamond composite
disc was then leached with acid reagents in a glass
beaker under the influence of heat and ultrasonic
agitation as described below. EDS analysis o~ the
leached compo~ite in a SEM indicated that all
intra-granular cobalt had been removed. Two procedures
were demonstrated to be effective, each carried out at
or close ~o the boiling point, 200F or higher, for
about 72 hours.
In the firs~ ~rocedure, a combination of HCl
and H20 (hydrochloric acid and water) in 50%-50% by
volume was madej into which combination H22 (hydrogen
peroxide) was added in 95%-5% by volume. Thi~ mixture
reacted vigorously with the diamond compact. ~s the
reaction s~bside~, more H22 was added and further
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treatment con~inued until the vigorous reaction no
long~r occurred. At that time the reagent was spent,
and the aforementioned steps were repeated until the
leaching was completed.
In the second procedure, a combination of HCl
and HN03 (hydrochloric and nitric acid) was made in
75%-25%, respectively, by volume and heated to boiling,
in contact with the diamond composite. Vigorous
reaction took place with the development o~ a strong
a~ber color in the solution and the evolution of dense
brown fumes. When the reaction began to subside, the
spent reagent was discarded and new reagent generatged
per the seguence described.
As may be seen from the above specific
examples of the practice of the invention, by the
introduction of a heat-treating step to the
conventional processing sequence for consolidating
finely divided diamond particles, it is possible to
rearrange and substantially reduce the number of
dislocations in the article that have resulted during
compacting to achieve a substantially strain-free state
in the article. In this manner, these dislocations do
not act as sites for crack nucleation. Consequently,
cracked propagation ~hat may result in catastrophic
failur~ of the article under conditions o~ applied
str~ re~ulting during the use thereo~ in typical
curring and drilling applications is avoided. It may
be seen, there~ore, that the inventive practices for
fabricating dense, consolidated articles of diamond and
diamond composites provide an improvement with respect
to conventional practices for consolidating such
articles, wherein both improved resistance to cracking
and improved wear resistance ~re achieved. It may
further be seen tha~ the inventive practice~ for
leaching the improved compacts impart additional
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advantages of improved thermal stability, as well as
superior fracture resistance.
