Note: Descriptions are shown in the official language in which they were submitted.
193~ R~-5662
METHOD FOR THE WORK-H~RDB~I~G OE' DIAMO~DS
BACKGROU~D OF THE INVE~TIO~
Polished sections o framesite, a naturally-
occurring bort type diamond present ceYtain surface
striations The nature of these striations is reported
in the article "Evidence for Plastic Deformation in the
Natural Pol~crystalline Diamond, Framesite" by R C
DeVries (Mat. Res. Bull Vol 8, pp 733-742, 1973). It
is pointed out therein that the narrow zones represented
b~ these striations are strain-hardened, are haxder than
any orientation o the diamond matrix and appear to indi-
cate the presence o oriented deformation bands within
the grains. It is concluded in the article that the
microstructure of framesite diamond is the result of
plastic deformation of diamond grains therein under
conditions such that brittle fracture was inhibited
U S Patents 3,141,746 issued July 21, 1964 -
DeLai and 3,136,615 issuecl June 9, 1964 - Bovenkerk et al
are typical of prior art disclosures relating to the
preparation of diamond compacts. In both of these patents
the provision of a bonding medium together with preformed
diamond crystals enables the unification of the diamonds
under the simultaneous application of appropriate pressure
and temperature conditions Compact formation is, as is
explained herei~below, the antithesis of the invention
described herein.
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RD-56~2
D~SCRIPTION OF THE INVENTION
The work-hardening of diamond cry tals~ a~
evidenced by the exten~ive development of deormation
bands in the surfaces of the crystal~, i8 accomplished
by filling a volume solely with di~mo~d cry~als (in
other words, no bonding medium 1B employed) or 801ely
.with diamond crystals embedd~d in a powdered mAterial
3elected from the group cons~ting of diamond and cubic
boron nltride and then subjecting the filled volume to
the simNltaneou~ application o~ high pressure and e~mper-
ature in a reglon defined on the carbon ph~se diag~m.Pressure and tem~erature condieion~ ~mployed in thi~
process are incapable of bringing about crystal-to-
crystal bonding o diamond (or o cubic boron nitride
pQyder, if ~mployed) o~ any conRequence. Thu8, after
the temperature ~nd pressure have been reduced, the work-
hard~ned diamond~ are readily separat~d for use in dia~ond
tools, for example, ~aws or single-point tool8t
The pressures and tamperntures employed m~y
range, for example, from about 10 kb at about 1200C to
about ~0 kb at about 900C~ When e~bedd~ng a larger
diamond erystal to be work-hardened In puwdered mater~al
as noted above, brittle racture thereof i~ inhibited.
As will be ~urther defined herein~ the Reglon of Plastic
Deformation in which the work-hardening of dia nd~ may be
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conducted includes temperature/pre~ure condi~ion~ both
in and out of the diamond ~table region. Preferred
operation i~ in that portion of the Regio,n o Pla~ic
Deformation below a pressure of 55 kb and at a temperatNre
of le~s than 1500C~
The size designation for diamond cry~tal~ a~
expressed herein is for the largest linear crystal
dimension~ The abbreviation "CBN" is used herein for
the term "cubic boron nitride",
BRIEF DESCRIPTION OF THE DRAWI~G
The exact nature of this invent~on a~ well as
objects and advantages thereof wil~ be readily app~rent
from consideration of ~he foll~wing ~pecification re-
lating to the annexed drawing ln which:
Fig. 1 represent~ the pha~e dlagram of carbon
having defined thereon the Region of Plastic Defonmatlon
in which the in~tant invention may be practiced and
Fig. 2 is a Nomarski interference ¢ontrast
photomicr~graph showing strain-hardened zo~es or l~nellae
20 proJecting above a surface of a diamond, which i8 approxi-
mately a ~135) planeO
MA~NER AND PROCESS OF MAKING AND USIM~
THE INVE~TION
One preferred form o~ ~ high pressure9 high
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RD-566~ :
temperature apparatus in which the instant: inven~ion m~y
be practiced is the subject of U~ S. Patent No. 2,941,248 -
issued June 21, 1960 - Hall and is also disclosed in
numerous other patents and publica~ions. Those skilled
in the art should, therefore, be well ac~lain~ed with
thi~ '~elt-type" appar~tus and, for thi~ reason, no eort
has been made to illustrate the apparatu~ in the drawing~.
Essentially9 the apparatu~ consi~s of a pai~
of cemented tungsten carbide punches disposed to either
slde of an intermedlate belt or die member o~ the same
materi~l. The space between the two punches and the die
i~ occupied by the reaction v~el and surrounding
gasket/insulation a3semblies therefor. High pres~ure~
are generated in the reactlon vessel from the c~mpre~si.ve
1~ forces caused by the rel~tive m~vement of the co-axially
dispo~ed punches toward each other within the die~ ~leans
are provided for heating the reactlon ve~sel during th~
application o~ pressure~.
Various reaction ve~sel conflgurations ar~
~hown in the pa~ent literature (e.g. U. ~. Pa ~nt NOe
3,423,177 - issued ~anuary 21~ 1969 - Boven~cerk., The~se
reaetion ves~el~ or cells, usually consist of several
inter~itt.ing cylindrical members and end plug~ for
containing the reaet-lon syst~m.ln the centermo~ cyl:inder~
In indirectly heated re~ction v~s~els one o~ the cylindri-
cal me~bers iB made of graphite~ which is heated by the
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RD-5~62
; passage of electrical current ~herethrough~ The r~ac~ion
mass is heated thereby~
Operational technique~ for s~multaneou~ly
applying both high pressures and high teml~erature~ in
such ~pparatus are well kncwn to th~e ~killed in the
superpres~ure art, There are~ of course, v~rlous other
apparatuses capable of providing the required pressure~
and temperatures thRt may be employed within the scope
of t'his invention
DiEmond i8 a brittle materlfll and cleaves easily
along (111) planes whe~ sub~ected ~o shearing 8tre~8. In
order to produce a wor~-hardened dia~ond, i~ i8 neoe8sary
to confine each diamond crys~al during the pres~ure appli~
cations so that brittle fracture i8 inhibi~ed as mNch ~5
possible, Tran~mission of the ~pplied pressure to the
dia~ond crystal itself need not be truly hydrostatic,
but the compscted crystal must be sufficiently w~ll con-
flned and the orce distri~u~ion thereover must be uniform
enough to avoid creating a larg~ unopposed shear ~or~e
acting in any one direction,
An optimNm BiZe range ~or the diamond cry~al
to be work-hardened i8 ~rom ~bout 5 ~icr~m~ters to ~bout
S millim~ters, A diamond crystal that ~8 too large m~y
crack, if it i9 not properly confinad and/or i~ p~n~i~t~d
to receive a non-uniform pre~sure distribution duril~;
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:~D-5662
conduct of the process. If ~he diamond crystal i8 too
small~ it may crack completely or m~y merely ad~ust lts
posltion ~o the application o~ pre~ure and no~ deform.
Both naturally-occurring ~Type I and Type II) and synthetic
(Type II) diamonds have been work~hardened by this pro-
cessO
Inhibition of brittle fracture of ~ given dia-
mond in order to maximize recoverable yield during work-
hardening thereof may be accompli~hed as follow8:
a) diamonds in the size range ~rom about
5 micrometers to about 250 micrometers
should constitute the entire charge
filling the reaction ves~el; each
crystal provide~ the requisi~e $upport
for ~djacenk crystale; u~ of a gradation
of sizes in the upper end of thls rsnge in
a given charge is preferable, but no~
critical;
b) diamonds in the Rize range from abou~
250 micrometers to about 5 mm should
be embedd~d in diamond or CBN powder,
; the combination of larger crystal and
powder constituting the en~ire charge
~illing the reaction volume and
., ,
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RD-5662
c) diamonds in a size range (from abou~ 250 to
abou~ 500 micrometers) may be work-harde~ed
u~ing either a) or b) aboveO
In the conduct o~ th~ method of this invention
using the "belt" apparatus ~he ~harge i placed in and
fills a cylindrical sleeve made of pyrophyllite, ~alt,
hexagonal boron nitride or similar material, th~ sleeve
i~ closed with end plug8 (preerably o the same material
as the cylindrical ~leeve, or enclosure)~ The sleeve is
then enclosed in the balance of the reaction ~essel (e.g.
within a graphite heater sleeve which, in tu~n, i8
surrounded by a sleeve of pyrophyllite or salt)~
Various hard embedding p~wder materials have
been tried (boron car~ide, ~ilicon carbide~ ~lumina,
pyrophyllite, tun~sten carbide~ diamond and cubic boron
nitride Diamond and cubic boron n~tride were the only
ones of these embedment material~ succe~fully employed
in the deformation of diamond by the present invention.
The size of particle~ for the embedment mater~al should
be in the range of 1/10 to l/100 of tha longes~ linear
dimension of the embedded di3m~nd.
After as~embly of the reaction ves3el and
introduction thereof in the high pre~sure~ high temperature
apparatus within the gasket/insulation a~emblies, pressure
and Eemperature are raised simultaneously or separate!ly
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RD 566~
(5-10 kb/min; 50-200C/min) to a level in the Re~ion of
Plastic Deformation defined in Fig. 1 and are held or
a period of at least about 1 minute~ e.g. in the range
of ~rom about 1 to about 30 minutes. Electric power to
the heater sleeve is shut off and ~he s~ple quickly
cools (in less than a minute) to below 50C~ The pre~,sure
is then released a~ a rate of about 10 kb/minr to one
atmo~phere for pres~3ures of 10 kb and abov~. For pre~3~ures
below 10 kb the release of pressure and the return to
atmospheric pre~sure is almost immediate.
As may be seen in Fig. 1, the Reglon o Plastic
Deforma~ion extend~ into both the diam~nd-stable and the
graphite-~table regions (i.e~ aboue and~below the line
indicated as the~Diamond-Graphite Equilibrlum Line)~ In
case of ~peration at pressure/temperature condLtions below
the diamsnd-~table region, but in the Region of Plastic
De~ormation, 00me graphitization of the work-hardened
diamond occurs s1mul~aneou~1y with the deformation,
However, in a 5-minute run, the ~m~unt of graphitlz~tion
has been found to be negligible. In a 15-minute run in
a pyrophyllite enclosure, a thin surface layer of graphite
has often been seenJ probably due to impurit:Les en~ering
the diamond charge from the pyrophyllite~
It is not uncommon for some breakage of diamond
crystals to occur during work-hardening, h~wever, diamnnd-
to-diamond bonding is to be avoided.
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RD- 566 2
Initially, diamond crystals were polished on
at least one surface prior to being subjected ~o de-
formation in order to establi~h the initial microstructure.
The diamond crystals were repolished on the same face
S after the deformation process to provide a c~mpari~on.
Later, it was determined that the presence o new de-
forma~ion zones could be clearly detec~ed by micro~copic
observation alone without prior or 3ubsequent polishing.
Crystals that are initially clear become cloudy and less
transparent ater dsformation, a change that is ususlly
apparent at 20X - 50X magnification,
To insure recovery of work-hardened diam~nds . ~`
intact from the embedment materi~lg pl~Gement o~ the
diamond in the emb~dment m~teri~l in relation to the
direction of the compressive force ~hould~be consider~d~
Thu~, an octahedron pl~ced in the c~ll with a set of
(111) faces disposed perpendicular to the dlrection o
the c~mpre~sive orce and th~n worlc hardened will almost
always delaminate9 because the crystal is gripped
sufficiently well by the embedment material to be pulled
apart by cleavage along the (111) plane as the punches
o~ the press separate on pressure relea8e~ On the other
hand with a ~100] axi~ o the ~c~hedron dlsposed parallel
to ~he axis of the piston~ (direction of compressive
force), most crystals are r~covered intact a~ter the
release of pres~ure 9 because the surrounding embedment
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RD-5662
powder pulls away from the crystal along the pointed
pyramids on either side of ~he girdle of Ithe octahedron~
Similarly~ cube-shaped crystals should be orientéd with
a [lll~ axis parallel to the axis of the pi~tons even
though this will orient a (111) cleavage plane perpendi-
cular to the axis of the pistons. If the llO0] axis of
a cube-shaped crystal is placed parallel to the axis
of the piston~, ~he crystal has a high probability of
delamination~ Using these geometrical criter-la in
placing the crystal in a cell, the recovery of work-
hardened diamond crystal~ completely intac~ from their
embedment is optimLzed.
After work-harden~ng, when the pres~ure and
temperature have been reduced to am~ient, the reaction
vessel is removed from the appara~us and ~he diam~nd
crystal content o the charge is recovered (i.e. dia-
mond crystals are separated rom e~ch other or from the
embedmQnt powder). The indications o deformation a~
seen by micro~copic observation ~ppear as straight
lines s~ightly elevated above the surface o~ the host
diamond and may be clearly seen in the photomierograph
of Fig.~ 2 extending in four different directions. -Each
of thes sl~p lines is the manifestation at the surace
of the iam~nd o~ a deformat~on zone or l~mella. In
~S general, the depth of the deformed reg~on i~ shallow
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RD-5662
(about 100 microns) but it is also common to ~ind
lamellae penetrating almost all the way l:hrough a
crystal as large as one millimeter. The pre~ence of
lamellae proj~cting above the surf~ce of a work-hardened
diamond crystal in four directions (or four different
crystal orientations) i9 typi~ied by numerical de-
~ignation~ 119 129 13, 14,
The deformation ~mellae introduce~ ln~o dia-
mond crystals by the practlce of this invention appear
to be ldentical in all respect~ to those earlier aeen
in ~ramesite. The lamellae were ound to be associated
with regions of high strain ba~ed on observation between
crossed polarlzers and the fact ~hat the l~mellae etch
preferentially in fused sal~,
Deformation lamellae or ~lip line~ were ound
to have a higher ~brasion resistance than even the (lll)
8ur~ace of the host dl~mond (the most abra~ive resistant
face thereof) and, this i8 the reason that these z~nes
pro~ect above the surface of~the di~amond ater po~ishingO
Example 1
A natural Type I diamond about 1 mm in greatest
dimension was embedded in 230/270 mesh s~nthetic diamond
in a high pre~cure cell~. This a~semblage was ~ub~ecte~
to a final pre~ure of 60 kb and a temperature of 800C
(in the dlamond stable region), The pressure and temper-
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RD-5662
ature were raised simultaneously at rates of about 3 kb/min
and 50C/min, respectively. After 5 minutes at ~he peak
temperature and pressure, the temperature and pres~ure
were decreased to room conditions and the crystal was
removed from the embedding diamond powderO The diam~nd
crystal showed no evidence of p~as~ic de~;ormation.
Example ~
The 3ame experimental ~echniques as in Ex~mple
1 were used uslng another diamnnd cry~tal measuring ~bout
1 mm, The peak pressure-temperattlre condltion~ were
60 kb and 1000C~ respectiv¢ly. These condltions are
in the diamond stable region. Upon removal of the dia-
mond cry~tal ~rom the polycrystalline diamond powder
m~trixS evidence of pia~tic deformatio~ was easy to see,
Slip lines were present, and the crystal was no longer
clear~
Exa~ple 3
A Type I natural di~mond (abou~ 1 mm) wa~ em-
bedded in 230/270 me~h diamond grains in a high pressure
cell, Thepre~sure was raised to 20 kb in about 7 minutes
simultaneously with a tem~erature rise to llOO~C in the
same tim~ The assembly wa5 held a~ the peak pressure -
and temperature for 5 minute~. These conditions sre in
the diamond ~table region. Upon rem~val of the d~amond
5 from the cell af~er quenching the power input to the
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RD-5~62
internal heater and then releasing the pressure~ slip
lines were observed in the crystal.
Example 4
A Type I n~tural diamond ~about 1 mm) was em-
bedded in 230/270 mesh diamond grains in a ~igh pressure
cell. The pressu~e wa~ rai~ed~ to 20 kb in about ~ mi~u~es
simwltaneously with a temperature rise ~o 900Cin the
same time, The assemblag~ was held at the peak pres~ure
and tempera~ure for 5 minutes. The diamond crys~al had
not been deformed by thi~ proce~ - i.e. no 91ip Iineg
could be seen. In the short dur~tion of this experiment
no graphitization was seen even though ~he pressure-
temperature conditions were in the graphite stabl~ region.
~ .
A Type II natural diaTnond (about 1 rmn) embedded
in 230/270 mesh synthetic diamond was raised to 50 kb
and 1200C at respective rates of about 3 kb/mln and
abou~ 100C/min simNltaneously. These maximum pressure-
temperature conditions were maintalned ~or 8 minu~es and
then decreased to normal ambient condition~. The crystal
was plastically deformed as evidenced by a heavy con-
centration of slip lines.
In the examples set ~orth in Table l ~aIow a
total of about 7.9 gm of clean 25/30 mesh synthetic
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RD-5662
equiaxed diamond crystals were subjected to pressure~
temperature conditions in the Region of Plas~tic Deformation
simultaneously applied ~or the times indicated, The~e
diamonds, which were of approximately equal ~ize, were
~rocessed in 16 runs consisting of about 0.5 gm each in
a belt-type apparatus. In each instance, after removal
of the reaction vessel from the appar~tu~ the work-
hardened diamonds were easily recoverable as discrete
cry~tals or la~er use, No ~raphitization wa9 see~. ~,f the
work-h~rdened diamonds recovered about 73% (5,8 gm) re-
mained on a 40 mesh sleve, ~he remaining 27% belng :Einer-
grained due to crushing during the deformation step.
TABL~ 1
Time
Run #'s P(kb) ~ (minutes~
73-138
to 40 1200 30
73 141
73-1~2
to ~5 1300 30
73-145
73-146
to 51 140~ 30
73-149
73 150
to 57.5 1~00 30
73 153
The physical appearance of a work-hardene~
diamond is noticeably dif~erent from lts appearance before
the deforMation bands were introduced. These changes i.n
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938
RD-5662
appearance apply whether or not the original clean cry~tal
has been reduced in size by crushing thereof. For smaller
crystals observation at relatively low pow~r m~gniica~`ion
may be needed to make th~s assessment~ Natural d~amond
5 crystal~, which may be colored, but are usually tran~parent3
became cloudy or frosty in appearance with attendant loss
in transparency. The frosty appearance is the result o
diffuse light~scattering rom the many new surfaces created
by deforma~ion of the crystal (i.e. the 81ip line~ shown
in Fig~ 2)& Synthetic diamonds are usually colored
(yellow, green, greenish-yellow, blue, blue-green, etc.),
h~ve ~urface etching from contact with the catalyst-solvent
during manufacture and generally contai~ impuritie~ in
varying degrees. The regions of clean synthetic diamonds
. ~
not etched or occupied by impurities are usually trans-
parent. After work-hardening, however, a definite re-
duction in transparency i6 noted, being replaced by a
frosty appearance due to diffu~e light~scatterlng that
prevails for the reason described above.
In the case in which diamond crystals of sbout
the same size are subjected to deformation usually ~ome
faces of each work-hardened crystal remains unchanged in
whole or in part depending upon the extent to which the
crystals have been able to press against each other~
However, there is no need in having each face plastically
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3 ~
~-56~2
defonmed to be able to produce tools that c~n present
substantial amounts of work-hardened crystalline area to
~he workpiece in an abrading or grinding operation.
Once these work-hardened diamond~ have been
recovered as discrete crystals fro~ the ~igh pressure,
high temperature apparatus, they can be s;2ed and graded
and used industrially in the same manner as such diamonds
have previously been used (l.e. in grinding wheels, saws9
files, single point tools, etc.) to abrade or grind
workpieces.
BEST MODE CONTEMPLATED
. .
It is preferred to operate in that portion of
the Region of Plastic De~on~ation (Fig. 1) defined by
line 10, line 11 (at 55 kb) and line 12 (at 1500C). In
those instances in which an embedment material i~ employed,
relative1y coarse diamond powder ~230-400 me~h) is pre-
ferred as the embedding medium.
OptimMm oper~ting conditions of pressure and
temperature lie in the diamond-stable region of the pre-
ferred portion of the Region of Plastic Deformation. Thiswould be an area on ~he carbon phase diagram defined by
line 10~ line 11 and the Diamond-Graphite Equilibrium Line.
The process of thi~ invention is best applied to
clean equiaxed ~i.e. blocky) diamond erystals. Inclu~io
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RD S66 2 : ~
., . ,,;
present in the crystals and/or the presence of e~ching
on surfaces of the crystal~ do not appear ~o have an ..
effect on the plastic deformation s~ep.
It is pre~erred, but not essen~ial" tO 8imNl-
~aneously raise ~ressure and temperature to the opera~ingcondition. Shortest effective defonmation times are preerredO
When diamond crystals in the 250-500 micrometer
range are used as the charge (non-embedment arrangement)
to the reaction vessel, packing of these crystals should be
optimized by using a gradation of crystal sizes.
The term "cleanl' as used herein (and in the
claims set forth hereinbelow) means being free of exposed
reac tive cons titutents .
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