CA1078196A - Diamond compacts - Google Patents

Abstract

Abstract of the Disclosure High-strength polycrystalline diamond compacts, containing no more than 2% by weight of material other than diamond, are prepared by a process which involves subject-ing fine diamond particles to positive ion bombardment or heating to a temperature in excess of 600°C., both in an inert atmosphere at subatmospheric pressure to produce what is believed to be particles having surfaces of ultra-high cleanliness and enhanced reactivity and then bonding the treated particles at high temperatures and ultra-high pressures.

Description

~D-925 ~f~7~3~
Thi~ in~ention relate~ ~o polycry~talline diamond compactc and to a proces^q ~or preparing ~uch compacts.
- Polycrystalline diamond compacts po~ considerablg potential impor~ance ~or use a~ a commer~ial abra~lve material.
A nwnber o~ such compact~ have been di~clo~ed, bonded by any ons of a varie~y o~ matrix materials or, in ~ome ca~, bonded directly to each other at ~rery high pr~s~ure3 and temperature~.
Such compact~ have not ,, how~er, achieved any commercial importance principally because o~ strength de~icisncie~0 10 Polycry~talline diamond al~o exis~ in natura in the ~orm o~
carbonado~. Such carbo~a~os are impur~ aggregat~ of ~ingle-cry~tal d~amo3ld~ held in a ma~rix o~ m~terial~ which ordinarily occur in the cru~t of ~he aarth in which the ~arbonado~ are fou~d. Thuq c~rbo~ado~ ~enerally hav~ a~ impuriti~ ~ilicate mineral~ or metal~ ~uch as aluminu~, copper, mangazle e, chromium, nickel, titanium, iro~ and magne~ium, u~u~lly in ~ompound form, in quantitie~ ranging from a ~r~c~ amo~ ~o several perc~t by welgh~ of th@ total dialao~d aggregate., The~e xlatural diamond aggregate~ are, ho~verg rela~ively 20 ~c~rce and, in ~dditio~, their ~tructure and propertie~ are ~on-uniform from aggr~gate~ to-aggregate~ and non-homogeneou-~ ~
t~ithin a ~Lr~n aggregats~ An anal~ o~ di~fer~nt port~ons o~ ~he 8ame~ carbo~lado blill disclo~e differen~ con~ti~uen~
den~i~ies and ~tr~ng~h propertie~. ~hile" th~refs)re, ~llch carbo~adoQ ar~ a u~eful arti~le of ~ommerce9 their utility ha~ bee~ 3eriously re3tri~d by both ~heir ~carci~y and the ~o~l-uniformity OI th0ir charact@ri~tlcs ar~d propertie~.
It has no~ been di~co~r~d tha~ polycry~talline d~o~ compaet~ dif~ri~g in certain important r~pe~ts from 30 th~ carbo~do~ fourld in nature a~ po~se~ing outst~ndirlg strength propertie~ may be prepared by first tr~a~ing the surface of a plural$~y o~ particl~ diamond~ ~o produce , D-92$

a surf~cs of ultra-h~gh cleanlines~ and enhanc~d reactivity and then bonding ~he treated diamonds by qubjecting them ~o a pressure in excess of about 50 kilobars, pre~erably ~rom 50 to 100 kilobar3, and a t~mperature in ~xces~ o~ abouk 1300 C., ~ pre~erably îrom 1300 to 3100 C. The diamond particles are cleaned to produce a ~ur~a~e o~ ul~ra-high cleanlines~ and enhanced reactivity by eith~r h~at~ng the diamonds at a tsmpera~ure in exce~ of 600 C. in an inert atmosphere at ~ubatmo~pheric pre~sure$ ~ or alt~rnativ~l3r, by 10 bombarding 3ub~tantially all sur~ac~s of the diamond particle~
with po~itive îon~ in an inert atmosphere at subatmo~pheric pres~re~. Both proce~se~ ~hould be perf'ormed in a dynamically pumped or gettered sy~tem~ otherwise, the contaminati~g ga~e~
~rill be reabsorbed on the dia~ond sur~ace and thl3 cleanir~g will be negated. After the diaraonds haYs bee~ ~hlls treated, they are compacted and hot-pres~ed at the pres~ and te~nparatur~ set forth abo~e, preferably in a high-pres~ure"
high-temperature apparagus of the typ~ used in the ~y~thetic productio~ of siIlgle-crystal diamond. Diamond compaGt~ ~e 20 prod~ced ha~e u~i~ormly high prop~r~ie~ both from compact--to-compaGt and within the ~ame ~ompaetD In addition, they e~ibit ~hear stre~gths o~ 50,000 to 90,000 pound~ per ~uare inch. This i~ in~ the range o~ s~re~gths mea~ d for good qualitg ~ le ~ry~tal~ of r~atural diamond aIld greater than that m~a~urod for carbonados., The compacts pos~e3~ a den~ity great~r than about 3.2 gra~s per ccO" ~hich i~ exce~ o~ -93% of ~he th~ore~ical ds~ y of diamo~d ~3~2 gram~ per ccO).
The in~sntio~ ~111 b~ more clearly under~ood ~rom the follo~g description ta~ken itl cor~tio~ ~ith the accom-30 panying drawi~g în ~ic~
- FI&URE~ a ~ ematic vi~w of an appara~u~ ~or modifying the ~ ace of diamo~d ~n accordanc~ ~h ~he

2 ~

~D 925 invention, ~nd FIGURE ~ i~ a sectional view of a reac~ion ~e~sel for use in a high-pres~ure, hi,gh-~emp~rature apparaku3 ~or bonding the treated diamond~ i~to polycry~talline diamond compast~ in accordanee with the in~ention.
The apparatu~3 shown in FIG. 1 may be u~ed ror cleaning ~he ~ ace diamond to a 3ta~e of ultra-high purity by positi~7e ion bombardment. E~en~ially, ~he ~ame apparatu~
may al~o bo u~ed ~or cleaning by firing ak ~ high temparature 10 eithor in ~accum or in khe pre~enc3 o~ hydrogen.
In th~ loII bombardm3n~ method o~ clea~ing, dia~ond~
are placed upon a pan 1 o~ titanium, molybdenum or cobalt ~onnected a~ a cathode ~hro~gh alumina in~ula~or 2 into the electrical circ~t relation~hip shown with power ~upply 3 and anoda 4~ Bell jar 5, af~ar b~ing placed in sealing eDgagement with ths surrace o~ ba~ plate 6, i~ evacuat@d v~ pipe 7 to ~ .
a pre~sure o~ abou~ ~ z 10-6 Torr or le~O After e~ra~u~tion, all inert gas, 3uch as argo~, h~lium or kryp~on, thal; will not be ad30rb~d appre~iably by th~ ace~ o~ m~erial within the 20 bell jar, i~ admitted ~hrough inlet 10 to a~t a~ ~he glo~
dl~eharg~ ga~ while ~he sy~k~m is being p~mp@d~, Sufficient inert ga~ i~ admitted ~o exert a pre3~llre o~ about 1~.0 1~5 x 10-2 Torr. ~t this pre~sure a vol~cag~ differential ~f 1000 - 2000 ~ol~s" and preferably from 1500 1~00 ~lt~, is imprs~ed betwa~ a~ode 4 and c~thode 1 b~ d.,c. po~er ~upply

- 3. ~h thi~ vol~age9 ga~-di~charge c~rrent~ are produeed su~ici~nt to cause cathod~ 1 to be bombarde~ b~ io~ havi~g very high ki~etic energi~, thsreby di#lodging fro~ ~he ~urface o~ the diamond a~ ad~orbsd ga~ parti~le or oxide coa~i2Lg 30 pr~ent ~hereo~. Du~i~g ~his pr~ce~, it i~ de~irable to ~gitate ~a~hode 1 ~o in~ure th~t ~he ellkire s~ ac~ of th~
diamo~d ;~ sxpo~ or a ~ eiently long peri~ ko the D-92$

bombardment of ion~ in order to e~ect complete cl.eaning thereo~. This may be dono by solenoid~actuated vibrator ~uring ion bombardm~nt. During the ion bombardn~en~, ~he bell jar is dynamically pumped by bleeding in puri~i~d inert ~a~
to ~weep the contaninatirlg ga~e~ out o~ ~;he bell jar a~d to main~ain the pre~3ure ~rhile ~he ga~es are cont;inuou~ly ~ ,h-dr~n and puri~i~d by p~sing ~hrough cold trl~lp30 In the high-t~mperature trea~ing method; the diamonds . .
ars placed in the ~ame apparatu~ on metal pan 1 Or titanium 10 or mol~bdenum which act~ a~ ~ crucible ~or suppor~ing the di~mond. Bell ~ar 5 i5 evacuated ~o a pre~ure o~ le~ than abou~ 1 x lo-l Torr~ If a hydrogen a~mo~phera i~ u~ed3 1~ i~
~ed through inlet 10. Th~ bottom ~ ace o~ th~ crucible is heat~d by radiation by a re~i~tance h~ater 9, con~isti~g o~ a spiral-~haped molybdenum coil, f'rom about 60û C. to 900 C.
for from about 30 minutes to an hourO Temp~ratures b~lo~ 600 C.
or aboY~ ~50 - 900 C. produce compac~ h grsatly r~duced ~hear ~trer~th. The pr~ure during th~ he~t~ng op~ratisn Dlay raxlge from 1 x 10-~ Torr (1 Torr = 1 mmO o~ ~gz ~ to a~ high 20 a~ 1 x 10~1 Torr, but in any ~ase ~ at all ~ime~ le~ than atmo~pherie~ The diamond~ ~hould be agitated duri~g the hea~ng cycle~ a3 i~ the ca~e of the positive io~ bombardment, so that all surfaces o~ th~ diamond cr~s~al are expo~d to the cleaning operation9 thu~ also in~ring e~Epo ~re OI all crystal~
to th~ temperatu;res measv;red ~t the center o~ ~he crucibl0.
III addition, the ~ystem i3 dynRmically pumped as in the ion bombardment method to pr~ent rea~orbption o~ ~ontamilla~ing ga~. Af`ter ~h~ diamond3 ar~ ~ool~ ~o room ~empera~ure, th~
vaccum ~y~em ~hould be back-gilled ~ h a~ i~ert ga~ before 30 openi~g ~o the atmosph~re,, A~r ~h~ diamollds hav~ been treated by either positiYe io~ bomb~dment or by the high-temp~rature treatm~Ilt,

- 4 ~ ~7 ~ ~ 9 ~ ~D-925 the di~monds ~hould not normally be expo~ed to air ~or period~
longer ~han about lg hours b~ore the high-pre~ure ~in~eri~g ~tep take~ place. It ha3 bee~ found tha~ ~xposure of the diamond~ for periods a~ long as 1~ hour~ does not detrimentally affect ~he propertie3 of ~h~ re~ulting compact~ It i~, how~er, pr~erable to p~r~orm the compactin~ operakion immediately.
Regardles~ o~ wheth~r the po~itiYe ion bombardm~nt or ~he h~ating m~thod is u~ed to clean and modify th~ diamond ~ur~ac~, ~he diamonds should be trea~ed in an ~tmosph~re which ha~ a partlal pre~sur9 of oxygen, nitrogen and water ~apor of 3~ than 5 x 10-6 Torr. In the ca~e of the h~ating m0thod~
the atmo~phere may be ~imply evacuated ~o that the propar d~gra~ o~ low pre~-~ure i~ ~rea~ed and mai~tained~ or the atmo~ph~re m~y ~on~i t of highly purifi~à hydrog~n. The hydro~en i~ pre~erably o~ ~lec~rol~kic origi~, and e~e~ more erably a "pr~ puri~i~d grad~n, and i~ ~hould bs pa~d throug~ a purifying cataly~ or ~ r ~uch ag p~lladium and a liquid nitro~ r~p to remoY~ oxygell and water ~apor from the hydrog~n~ ~-Bo~;h the haating a~d th~ lon bombardm~nt ~tep~
hav~ hereis~ been referr~d to ~or br~vi~y a~ ultra-high purity or cleaning ~ep~. Consid~rable efi~ort ha~ been mad~ to undsr~tand th~ m~chanl~m by which th~ great~r bond i$ achi~ed when diamond~ are thu~ treat0d9 inclu~ing r~view of chemical ~nalyse~ and bo~h X-ray and el~ctro~ diffrac~ion skudie~ ~f the ~ur~ac~ o~ khe t~atod dia~ond~. Ho~eY~r, the e~act ; change oc~urrin~ aft~r th~ h~ing or ion bom~ardment ~p~
i3 ~till no~ clearly under~cd~ It i~ believed that a sur~a~e modification t~ke~ place o~ ~he diamond cry~tals ~h~n tr~ated -. in accordan~e with ~he inve~io~, and that th~ modificatio~
includ~s a r0mo~al of solid and/or ga~ou~ ~ilm (e~gO~ non~

- 5 : -8~
diamond carbon, adsorbed oxygen or other atmospheric gases) that inhibits bonding of untreated diamonds, even when they have been chemically cleaned. In addition, a thin layer of the surface of the diamond crystal is disturbed in such a way that the regular array o~ carbon atoms is distorted. Low angle X-ray diffraction analytical methods indicate that diamond so treated has a thin layer of "amorphous" structure.
Thus, the reference to ultra-high cleaning, while believed generally descriptive, should not be construed as limiting with respect to the process.
Following the ultra-high cleaning step, the now-clean diamond particles or crystals, with or without a small amount of ~atrix material, are ready for the sintering or compacting operation in a high-pressure apparatus. The -sintering step is carried out at pressures in excess of 50 ; kilobars, preferably about 65 to 100 kilobars and temperatures in excess of 1300C., preferably about 1800C. or higher, for periods of time ranging from about 10 to 30 minutes. One suitable apparatus for carrying out the sintering operation is disclosed in UOS~ patent 2,941,248 - Hall. A reaction vessel suitable for use with an apparatus of the type shown in the Hall patent and which may be used for preparing polycrystalline diamond compacts in accordance with the present invention is shown in FIG.
2. The reaction vessel 17 is of the so-called indirectly heated type having a pyrophyllite outer cylinder 1~, a graphite heating tube 19 placed concentrically within cylinder 18 for indirectly heating the sample to be subjected to the high temperature-pressure operation. A further cylinder 20 of alumina is placed within the graphite heater tube 19, and finally a graphite inner liner 21 is placed within the alumina. Graphite end plugs 22 and 22' and alumina end plugs 23 and 23' fit within the upper and lower portions of the graphite inner liner and the alumina .: . .
-- 6 - .

~D-925 cyli~der respectivoly to support ~hield and insul~ the compon~nt~ o~ the reaction ves~el.
Our experiments indicat~ that the sinterî~g operation i~ be3t p~rformed in an inert container or prefer~bly one in which a reducing atmo~phere is pre~ent during the ~intering.
For thi~ reason, we have chosen a ~raphite-lined reac~ion ~e~s~l. If ~he graph~t~ l~nar 21 is not pre~en~ ~nd khe p~rticlea to be compacted are in contact with the alumina 20, it ha~ been found bhat ~ compact of low~r ~trength will resultO
Tho raason i~ th~t tha alumina provide~ a ~ourc~ o~ oxyg~n to recontaminate the diamond; pre~enting a good dia~ond-to-diamond bond, ~herea~ graphit~ i~ a good g~ttar for oxygen and tend~ to maintain the atmo3phere in the react~on ~e~el - rsd~ing durlng the sintering ~ro~e~. Ther~ are altornat~
~chem~ to do this, suGh a~ providing a ~itani ~ getter o~ a metal of ~imilar characteriqtie~. Fur~hermore, it ha~ been fo~nd khat it is important to ~h~ld the di~mond ~rom contamination ~hile ~i~teri~gO The alumina lin~r plu~ th~
graphi~e li~er, ~eparately a~d in combinati~n~ provid~ ~hield~
~or the diamond from decont~ination produc~ o~ the heated pyrophyllite ~tone. Other ~hield3 or barrier~ could be u~d in placs of the abo~ material~ or ln ~ddition ~e ~hemj 3uch as ~ap~ul~ o~ re~rackory metal~ lik~ tan~al~m, t~ng~ten, molybdenu~, titanium or zirc~ium.
The pr~ures ~hich should be u~ed in prep~rin~ the compact~ of the invention are based upon a ~libratio~ procedure ~hich i~ r~lated to known ele~tri~al resistanee changes o~
~ariou~ metal~ at room te~para~ure und~r kn~ pr~sure~ a~ :
de~crib~d ~nd illu~tr~d i~ ~he a~or@men~io~ed U.S. pa~n~
2~941,24~ and as modlfied b~ correcti~g the ~al~bratio~ a~ :
ds~cribed in ~Calibrat30~ T~eh~iqu~ Ultra High Pre~r ~pparatu~, F. P. Bu~dy, Journal o~ ~ngineering for Indu~t~

78~.916 ~D-925 May, 1961, Tran~actions of the ASM~, Serie~ B.
In a typical po~iti~e ion bombardment cleaning method, a one and one-half` gram sample of minus I~OO me~h (U.S. ~tandard~
sliamond single crystals wa3 placed 02~ a ~itanium ca~hode pa~
fabricated fro~ 0.015" ~hick ti~anlum shee~. The diamond-containing pan was placed ~rikhin the bell ~ar o~ an apparatus as shown in FIG. 1 oî the drawing. A 1-1/2'~ diame~r ~i~anium anod~ di~c wa~ placed 3~4 to 11l above th~ c~thode rim. The be~l ~ar was lo~red o~rer the elec~rode as~embly, and the 10 ~ystem ~a~ e~acuated to a pres~ur~ of about 1 x 1O-6 Torr.
A~ter the vacuum ~y~tam bad b~n pumped under th~e co)lditi~s ~or about lO minut~, highpurity (99~997% a~say) ar~on gas ~RaS introduced into th~ ~y~t~rQ through inl~t pip~ 10. Argon wa~ leaked into the 3y~t~m at a r~t~ corre~ponding to a dyn~c sy~tem prs~ of 1 to 1.5 :c 10 2 Torr. Th~ diamond crys~ wer~ agit~t~d m~chanically by the solenoid;type vibrato~ llrhile b~ing sub~ct~d to ion bombardm~ntO A negative .~ pot~ntial of 1500 ~olts was impre~s~d on the diamond-co~tai~ g re~eiv~r ca~hode for one hour. The titanium ca~hode ~urrent dell~it~r during sample bombardme~t wa~ ~ypically 6 x 10'5 to 1.5 x 10 4 amp./cm2.
A~ter the ~ample h~d be~n ~xpo~ed to argon lon bombardment îor îrom 1/2 to ~-1/2 hours, th~ vacuum sy~tem ~ras back-fi11~d with high-puri~y grads argon and the~ o~elled to tha atmosph~r~. The e1eaned diamond cry~ta1~ were then manually pa~ked into ~he gr phi~e 1ined, indirec~ly heated ~mple ho1d~r shs~ .~ 2, and s1ntered at pres~ure~ of ~out 65 to 70 ki1Obars at ~emperature~ of ~rom 1500~ to 1800 C.
In a ~ al ~xample of the preparat10n o~ a d1am~nd cvmpact by fir~t heatillg in hydrogen or hi~h vacullm9 a one-~ram ~alllpl8 oi~ mi~u~ 400 rae~h (U.5. ~kandard) diamond ~ingle .; ~................................. , 1~78196 ~D~g25 crystals w~s placed in a m~tal crucible fabricate~ from 0.010" thick titanillm or molybdenum ~hee~. The crucibles were supported in~ide ~he b~ll jar by a molybdenum wire~ The bottom ~ ac~ of khe crucible ~ra~ heated by radiation :~rom spiral-shapsd heating coil 9 located about 1/16~ below the bottom ~urface of ~he ~rucible. All t~mperatur~ wera mea~ured by mean3 o~ a thermocouple w~ld~d to the cent~r of th~ top surface o~ the metal cruc~ble. After ~he dlamon~ cryætals ~ere plac~d in ~he mstal cathode, ~he bell ~ar wa~ lowered and evaeuated to about 5 x 10-`6 Torr pres~ure. I~ a partial pre3~ oi~ hydro~en wa~ us~d, ~he hydrogen wa~ drawn ~rom a tank o~ pre-purified grade hydrogell pa~ed through a palladium ~athalyst and then through a liquid nitrogèn ¢old trap to remo~ an~ water vapor formed from oxygeli. The heatiIlg ~
carried out to temperature~ o~ ~rom 60C) to 903~ C. ~or ~rom 30 to 60 minut~ while th~ hy~rogen wa~ beillg ~wept through the bell jar. The ~acuum ~ys~em w~ then back-filled ~i~h purifiad arg~n a~l opened ~o ~he atmQsphere. The dia~no~d~
w~r~3 th~n ~i~tered at high pre~ and t~mperature~ i~ the ~ame manrller a~ ~he clia~ond~ which had bea~ cl~aned by ion bombard:~ent .
The diamo~d~ ~rom w~i~h ~he polycry8tal1ine diamo~d compa~ts ar~ prepared may b~ either natural dismonds or diamonds ~ich are prod~ced ~ynthetically~ Th~ ~tar~ing material ~ay b~ singl~-crys~ iamond~ or a mix~ure o~ gle-cry~al diamond, ~ned-~r~tal diamond or eve~ ~mall diamo~d polycrystal~. The ~iamo~d particles should ha~ a 3ize o~
pre~rabl~ lea~ than lû~ micro~3, and e~en mor~ pre~erably a ~i~e ~maller than 40 micro~ Th~ ~pecific nîcron size oî
~he diamond 3i~gle cry~tal~ ~lect~d ~rill, of cour~e, b~ :
d~pendant on gh~ application i~t;en~ed f~or ~h~ polycrystalline diamond compac~O It i5 also desirable to use a ra}~ge o~

g :

. .

78~L~6 ~D 925 particle ~i~e~ to achieve high initial packing d~nsitie3 according to known procedures. In many inætans8~ may be necessary to clean ~he diamond powder chemically prior to subjecting it to the cleaning proces3 oî the pre~nt in~ntion.
Such chemical cleaning may be performed by m~an~ w~ll kno~m in the art, as ~or example by the use o~ hydrochloric acid or aqua ragia or by other acid treatmentO
The diamond may be compacted, if de~ired, in conjunction with a ~mall amount of an add:i ti~re m~1terial either 10 in the Iorm of a matrix or a coating on ~he diamond crystal~.
Among ths matrix materials whi~h may be u~ed are boron, tantal~Dn, molybd~num, and titanium or their carbides and boriàes.
For example, boron carbid~ (B4C) may be u~d in amour~ rom about 0~2 to abouk 0.~% by weight, boron i~ amount~ ra~ging from about Ool to about 0.6%~ or titaxlium boride (TiB2) in amou~t~ rang~ng as high a~ 1% by ~ight o~ the PQ1~CSY~a11i~e diamond compa~t. Molybdenun, tit~ am, niç}cel, anà th~ir alloy~ ~re lllu~tr~ive coa~ing mater1al3. How~ver~ kh~
compacts ~hould not con~airl in ex~e~ o~ abou~ 2%. by total 20 ~ight o~ ~he compac~ o~ material other ~ha~ single-cry~t~l -- diamond. Compaots containing more than 2% o~ such material do not pOJBeBB th~ requisit~ str~rlgth properti~s.

~ .

, - 1~

Claims (7)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A process for producing polycrystalline diamond compacts comprising: heating at a temperature in excess of 600° C. a plurality of fine diamond particles while said diamonds are maintained in an inert atmosphere at subatmospheric pressures, compacting the treated diamonds at a pressure in excess of 50 kilobars and a temperature in excess of 1300°C.
to form a high-strength coherent polycrystalline diamond compact.

2. The process of claim 1 in which the diamonds are agitated during the heating step.

3. The process of claim 1 in which the compacting step is carried out in a reducing environment shielded from contamination.

4. The process of claim 1 in which the diamond particles are of less than 40 micron size.

5. A high-strength coherent polycrystalline diamond compact consisting essentially of a plurality of fine diamond particles and no more than 2% by weight of material other than diamond, said compact having a density in excess of 93% of the theoretical density of diamond, the structure and density of said compact being homogeneous throughout.

6. The diamond compact of claim 5 having a shear strength in excess of 50,000 psi.

7. The diamond compact of claim 5 in which the diamond particles are of less than 40 micron size.