CA1066512A - Solution-precipitation process for manufacturing abrasive bodies - Google Patents

Abstract

SOLUTION-PRECIPITATION PROCESS FOR MANUFACTURING
ABRASIVE BODIES

Abstract of the Disclosure Hexagonal boron nitride (HBN) is converted to cubic boron nitride (CBN) within a transition metal alloy solvent system containing a small percentage of aluminum.
Precipitous drops in the conversion of HBN to CBN occur as the ratio of the weight of HBN to the weight of metal in the initial mixture increases beyond some maximum yield ratio that may be routinely determined for each alloy. An abrasive body is produced in which the binder for the CBN grains is the metal alloy solvent itself, e.g.
a superalloy.

Description

jS~'2 SOLUTION-PRECIPITATIO~ PROCE'~S FOR M~NUFACTURING
ABRASIVE: BODIES

BACKGROU D OF THE INVENTION

The method of converting hexagonal boron nitride (HBN) to cubic boron nitrida (CBN) employing at least one catalyst selected from the class consisting of alkali metals, alkaline earth metals~ lead, anti~ony, tin and nitrides of these metals is describad in U.S.
Patent No. 2,947,617 - Wentorf, Jr. - issued August 2, 1960.
The use of Fe3Al and certain silver-cadmium alloys as catalysts in the conversion of HBN to CBN has been described in "Synthesis of Cubic Boron Nitride" by Saito et al (Yogyo-Kyokai Shi, Vol. 78, No. 8~3). `
The use of aluminum alloys of cobalt, nickel -~
and manganese as catalysts for the conversion of HB~ to the CBN form at high pressure and high temperature is ~A disclosed in U.S. Patent ~o. 3,4/~,~lq Wentorf~ Jr. et al issued ~ove~ber //, /~7~ and a3signed to the assignee of ~ ~
the instant invention.
The term "minimum composition" is that alloy composition for a given alloy system at which extensive solid solution is obtained at tha lowe t temperature.

.- ' 10665i2 RD-5823 The tenm "room temperature" is intended to mean a temperature in the 70-75F range, "Quenching" means in~tituting a rapid drop in temperature. Wlth the appara~u~
employed herein 8 temperature drop of about 1500C/minute can be achieved by simply turning of ~he power to the reaction vessel with the preB~Ure 8till ~pplied.

D~SCRIPTION OF TQE I~VENTION

This invention is an improvement over the in-ventlon in the Wentorf9 Jr. et al application. The product -`
produced from the process of this invention is a solid abr~sive tran~ition metal-aluminum alloy matr~x body con- ;
~isting of small well-formed CBN crystals distributed uni^ ~`~
fonmly through the metal binder phase. Convers~on of HB~
to CB~ as high ~8 93 per cent h~ve been achieved. These capabilities depend upon the discover~es (not disclosed in Wentorf, Jr. et al) tha~:
a) at pressures and temperatures at which CBN
i8 the 8 t~ble ph~se, ~BN dissolves quickly in a number of alloy sy~ems made up of a small amount of aluminum ~ogether with at lea~ two metals from the group eon~isting of chromlum, mangane~e, iron cobalt and nickel;
the alloy system becomes super~aturated with respect ~o aBN and the CB~ precipi~ates;

b) when the wei~ht per cent of HBN to be used in the HBN/alloy mixture i~
properly selected wlthin the 10-SO
weight per cent (w/o) HBN range9 the m~ximum CBN yield for that glven operat~ng temperature and specific alloy can be ob~ained; the op~im~m w/o HBN is routinely determinable or the p~rticular . .
~lloy to be employed and this determlnation should be made, becauRe r~m~rkably 8teep drop~ in yields have been unexpectadly e~-countered in esch in~t~nce, when increa~ing amount8 of H8N are employed, the peak value :
being encountered in the aforementioned w/o rnnge; ~.
c) the operating temperature should be the lowest temperature at wh~ch ~11 of the alloy will be melted st the operating pres~ure whereby maxlmum liquid formation of the ~lloy will be ~0 made avallable, becau~e yieldQ of CBN appear to decrease with increasing temperature, and d) by utilizing all cornponent materials ~HBN, - preformed ~lloy or lndividual alloy components) in powder form, well mixed to produce fairly unifonm d~8tribution~ the CBN ry8t~18 pro-~- -"

, . ~-~- ~ . . . . . ...

~ ~ ~ 6 5~ Z RD-5~23 duced are well-fonmed, more equl~xed with individual face development and ~ee o~
gro~ defect~.

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When the properties (e.g. ~oughnes~, hardnesa, etc.) of the alloy binder are to be op~imiz~d, the speclfic composition o the trsnsition metal alloy will be selected -from ~he phase di~gram for the alloy sys~em. Otherwl~e, for convenience, the composit~on o~ the transltion metal alloy i8 selected by choosing th~ bin~ry or ternary eutectic or the minimNm composition o the given alloy system, Once the speciic combination has been selected, a 8m~11 amount (le88 th~n 5 per cent) o~ aluminum i~ added ~hereto.
The aluminum can be added as aluminum metal, AlN or A14C3. ~ ~
When the eutectic or minimum compositions for the given ~ -alloy system can be used~ maximNm liquld formatio~ can be obtained a~ the lowest temperature and this, ~n turn, ~ ~;
help~ in ma~mizing the yield of CB~. The percent~ge o~ ~-HBN converted to CB~ i8 a function of the ~lloyr the pressure-temperature conditlons and the initial amount of HBN.
The ~etals listed hereinabove for the alloy : .
formation are used, because they do not fonm such stable nitrides and borides ~s will r~dw e ~he availabilLty of nitrogen and boron at~m ~t ~he CB~-metal lnterface or slgnificsntly reduce (by dlssolution) th~ ~mount of CBN4 ~ 6 6 ~Z RD-58~3 The method of thi~ inven~ion com~rises the following steps:
1. mixlng HBN powder wlth a powdered metallic phase to produee a homogeneous mixture, the atomlc con~ent of sa~d metallic phase consisting es~entially of aluminum atoms, atoms of a metal selected from the group consi~ting of chromium and manganese, and atom~ of at least one metal ~elected from the group consisting of ir~n, cobalt and nickel~ the we~ght per cent of HBN ~`-in said mixture, being in the range of from about 10 to about 50 weight per cent;
20 pressing ssid mixture into ~ome predetermined shape; .
3, simNltaneously subjecting said mixture to an ~ :
operating tempera~ure and operatlng pressure within the stabil~ty region of CBN defined by the use of the selected metallic phase, the operat~ng temperature being h~gh enough ~o render molten all of the metalllc phase, the period o~
time of simNltaneous temperature and pre3sure application belng sufficient to permit dis-solution of all of the HBN in the molten metallic phase and the precipitation of CBN crystal~ : .
thèrefrom; ~ -4. quenohing the`resulting CBN/alloy system to about room temper~ture while maintaining the oper~tlng pressure;
- ~ :

~66~1Z
D-sa23 ~, 5. reducing the pressure to atmospheric pres~ure and 6. recovering tha preshaped abrasive body consist-ing essentially of CBN crystals distributed in a ~lansition metal-aluminum alloy matrix. ~`~

The minimum pressure for the conversion of HBN
to CBN has ~een found to be about 45 47 kb regardless of tha specific metallic phase (unalloyed mix or pre-fonmed alloy~ employed, but the minimum temperature varies. Thus~
once a metallic phase formulation has been selected it is preferable to detenmine-the Pressure-Temperature Stability ;~
Region for CBN for that given formulation. A represen~ative P-T phase diagram for bo~on nitride showing CBN-stable and ,~ HBN-stable regions is shown in Fig. 1 of the Wentorf ~ -patent. Such a phase d~agram is routinely detenminable for a given metalllc phase formulàtion by one skilled in the high temperature-high pres~ure art, In order to determine the w/o HBN for maximum conversion to CBN for the specific metallic phase the above me~hod step~ were repeated using a number of different weight percen~ges of HBN. The CBN produced in each abras~ve body was recovered by scid dis~olution of the alloy portion. If the chromium content of the alIoy was low, aqua regia or dilute hydrochloric acid was used. If the chromium content w~s high, solutions of H2S04-H3P04 8C ids were used.
6 -- .

~ O ~ 6 51 2 RD-5823 As may be seen from the data set forth belowg the percentage yield of CB~ increa~e~ sharply wi~h increasing w/o of HBN in the mlxture, reache~ a peak and then falls off in a very steep ,drop in per cent yield that was not expected and is not understood. In principle a continued increase or a leveling off in yield would have been expected. Th~s peaking out and sharp decre~se in CBN yield occurs in the 10-50 w/o HBN range regardle~s of the alloy solvent.
Table I below shows the per cent yield o CBN
obtained aB a function of increasing w/o of HBN in the mixture. In the various runs the powders for y~eld~ng the alloy composition (46 w~o Fe, 32 w/o Ni, 21 w/o Cr and 1 w¦o Al) and HBN po~Jder were mlxed and pressed into a cylindrical shape in a m~ld and were then subiect~d to tempera~ures in the 1440~1460C range and pressures in the 50-55 kb range. After lowaring the temperature and pressure, a-cylindrical abrasive body ~CBN grains in an alloy binder) was removed fr~m the reaction ve~el rem~ins. The metal wa~ d~ssolved away in acid and the remaining C~N was weighed. -7 ~
' ~ .

, . ~ ' ~ S~'~ RD-5823 TABLE I
Metal. HBN HBM Timle Yield (~ms) (gms~ w/o (~min~ (Z) _ 1076~ 0.0251.4 120 12 ~oS7 0.050 2.~ 71 26 1.~70 0.1~0 6.4 }20 48 1.270 0.15010.6 80 S9 1.080 0.20015.64 120 70 0.876 0.25022.2 80 B3 0.804 0.27025.0 80 ~-25 0.684 0O30030 D 5 77 9.3 0~300 0.400S7.2 12011.8 T~ble II shows changes occurring in CBN
yield as the w/o HBN in the mixture was variedO As above, powders were combined to yield the reguisite 2110y (3902 w/o Ni, 5808 w/o Mn and 2~0 w/o Al) in :~
~itu. Preparation and shaping of the mixture to be converted to the abrasive body ~nd determination of CBN yield were as de~cribed above~ The conversion was conducted at 52.5 kb and 1450~Co , ~ 66 5~ ~ Rn-5823 TABLE II
Metal ~BN HBN Time Yield ~ms~ ~8~ (w/o3 (m~n~ (%) 1~470 OolOO 6~4 60 31~0 1~07~ 0~200 15~6 60 88~5 0~684 0~300 .30~5 60 91~0 ~)~486 0~3S0 42~0 ~iO 79~4 ~``
- 0~ 4 00400 570~ 60 2600 Table III and Table IV are derived from data obtained a~ in Tables I an~ the me-tal alloy com-position for Table I~ was 49 w/o Nl, 49 w/o Cr and ~-

2 w/o Al and the metal alloy composition for Table IV
was 8 w/o Fe, 43 w/o N~9 47 w/o Cr ~nd 2 w/o Al. The opexating temperatures were 1450C and the operating pressure~ were 52~5 kbo T~L~
Metal HBN HBN Time Yield 1 ~ 470 0 ~I 100~i o 4 60 1~; o 2 1 ~ 0725 0 o 200 ~5 ~ 7 60 53 o 8 ;
0~684 0~300 30~5 60 621~5 ~ ~ `
0~486 ()~350 ~1 ~9 60 700 2 `
0~294 0~400 57~6 6() 34~1 0~096 0~450 82~4 6~) 201 :';''' .' ,' ' ' ','-,. , ' ' '" , `'` ''`"";"' ,''','` - ' ' ' ' ~ -:

~665~2 TABLE; IQ
Metal HBN HBN Time Yield (~s? ~ ~ ~1l? ~ ~ ~
1 . 627~ Oo 0603 . 56 50 0 51 .4679 O. 100 6 .4 4~ 16 1.2728 0~50 10.5 73 38.8 1.0781 00200 ~5.7 ~7 57.0 `
. 8~11 0 . ~5022 . 1 77 67 . 5 ; ~:
~ . 6834 0 ~ 30030 . 5 ~0 82 ~, 5 100.4916 0c350 41.6 60 93.0 .3gO 0.375 4g.0 ~0 7~.0 002878 0.400 58,2 73 55.1 . ~ .

Data for Table V was obtained as deqcribed hereinaboveO The me~al alloy resulting from the- powders ~ -was 3902 w/o Fe, 58~.8 w/o Mn and 2.. 0 w/o Al~ Operating condition3 were 52. 5 kb and 1450~C .
TABLE V
Metal HBN - NBN Time Yield (gm~ ms) ~w/o~ (min2 (%2 1 . 470 0 . 100 6 . 4 6~ 53 . 8 ~;
1 . 074 0 0 20015 . 6 ÇO 82 . O ~ . :
O ~ 684 0 ~, 30030 ~ 5 60 85 . 9 :
0.588 0.3~5 35.fi 60 90.6 ~`
O . 486 0 ~ 3504~ . 0 60 13 0 . 294 0 . 40057 . 0 60 6 . 4 .

- 10 , .

~06G5i2 One preferred form of a high pressure, high temperature apparatus in which the method of the instant invention may be practiced is the ~3ubject of U.S. Patent 2,941,248 - Hall and issued June 21, 1960 and is well-known in the art as the "belt apparatus". Essentially, the apparatus includes a pair of cemented tungsten carbide punches in opposed rslationship to each other disposed on opposite sides of an intermediate belt or die member, and are aligned with a hole through the die mem~er having tapered sides. The space between the punches and the wall of the hole accommodates a pair of gasket/insulating assemblies, which in turn surround a reaction vessel.
The gasket/insulating assembliQs are typically made o~
thermally insulating, electrically non-conducting pyrophyllite and include means by which electrical energy may be con-trollably applied to the system to provide the requisite `~
heating of the reaction vessel~
Preferably, with the exception of the heatsr, which is usually made of graphite, the reaction vessel parts to be amployed in the conduct of this method should be made of ~odium chloride, although other matarials such as talc, potassium chloride, etc. as described in U.S. Patent

3,030,662 - Strong, issued April 24, 1962, may be employed. Techniques for calibration of the device for pressure and temperature are well established in the literature.

~ ~ , 1 ~ 6 6 512 RD-5823 The produot o~ this process is a ~olid body recovered in ~UmQ preselected form and consi~ting of small well-fonmed CBN cry~tal~ distributed uniformly through a met~l binder phase. The volume per cent of abrasive grain present therein may be readily made as high as about 55 per cent by volume o~ the abra~ive bodyO
Some ~mall amount of boron nitride remain~ olu~ion in the metallic phase ~counting for the 8m~11 dlfferential between the HBN present in ~he original mixt~re and the amount of CBN recovered when the met~l phase ha8 been dissolved aw~y to determine CB~ content.
Abr~ve bod~es produoed by the practice of this inven~ion have been utilized to grind sapphire, s~licon carb~de, cemented tungsten c~rbide~
steel ~nd quartz. For convenience in brazing, these abrasive bodie~ have al~o been formed as compo3ite~ having a layer on one surface thereof of the solvent-binder alloy employed. Thls metal surface has been successfully brazed into a holder for mounting of the abrasive ~ody for use in revolving machinery. Such composites m~y be advantageou~ly bra~ed into saw blades and coring tools~
Further, since the metal ~olvent-binder is acid soluble~
the abrasive grain at the surface of the abrasive tooI may be readily expo~ed by dipping ~he tool in a dilu~ acid ~olutionO

~0 ~6 51 2 RD-582~

Thi~ method i~ particularly advantag~ous bec~use the matrix for the complcted tool serve~ as the 801vent from which the CBN crystal~ appea:r to be precipitated.
The HBN i~ rapidly soluble ther~in at the operating pressure/temperature cond~tions, This preparation of the CBN crystal by precipitat~on fron a metallic solvent that remains as the binder promotes cxcellent ~etal-to-grain contac~ (no we~k intermediate phases~ resulting ~n ~uperlor bonding between the b~nder and each abrasive crystal. The ability to u3e a ntmlber of transition metals for tha con-duc~ of the conversion of HBN to CBN enable~ the selection of m~ny alloy ~y8tem8 from among ~he superallQys and stainless 8teels. Superalloy mstrices, in particular, provide very tough 801vent-binders or CBN grains. Con-duct of the method of the instan~ invention fo~ ~he pre~
para~ion of abrasive bodies in which ~he binder is a - supe~alloy composition ~8 en~ompa$sed within the best mode :~
of thi~ invention as desc-r~bed he~ein~elow.

~ `~
~ High melting alloy systems that have been effect~vely employed in the practice of this inven~iorl ars the iron~niekel-chromium-aluminum 8ystem; the nicke~-chromium-aluminum system and the nickel-manganese-aluminum syst~m. :-The ~mount of aluminum employed will preferably - 13 :
~ .

.. . ... .. . :: -Sl~ ~ ~
be less than 5 w/o in the aforementioned alloy system and as such will not seriously affect the eutectic or minimum melting compositions for the systems.
Thus, the minimum melting composition for the iron-nickel-chromium-aluminum alloy system is about 1315C (at one atmosphere); the minimum melting composition for the nickel chromium-aluminum system is ab~ut 1345C ~at one ~
atmosphere) and the minimum melting cmposition of the ~ -nickel-manganese-aluminum system is about 1010dC (at one atmosphere).
Specific combinations of the metals set forth above have been successfully employed for the preparation of abrasive bodies. Once the pressure was applied to the reaction vessel the temperature thereof was raised to the desired value in a period of from 1 to 4 minutes and was held at the operating temperature. Quenching to room temperature was accomplished with the pressure applied to the system.

0.282 gms of HBN and 0.396 gms of metal (58.8 w/o Mn, 39.2 w/o Ni and 2.0 w/o Al) were mixed and pressed into a pellet about 0.250" high x 0.250"

diameter. ~BN constituted about 42 w~o of the (metal ;~
''` -'' ': :
:~, ';

~. .
,.' ;~

~3665~

plus HBN) mixt~re. A separate disc ~0.060" deep) of met~l alloy powder only wa~ placed against the BN-met~l pellet and both were simultsneou31y ~exposed to 52.5 kb and 1450C for 30 minu~e~. CBN grain~ precipita~ed in the pellet and the metal ~lloy dlsc bec~me firmly bonded together and bonded to the abra~ve~containing portion.
Thi8 metal alloy "pad" was silver-soldered to a steel cup hsving a 1/8" x 1" shuft ~ttached thereto to produce an abrasive tool. The abrasive gr~itns were exposed (i.e.
10 the wheel was "opened"~ by etching the surface for 3 minutes ~n aqua r~gia. This tool when mounted in a ro~ating machine 3uch as a drill easily ground a steel file, a 8apphire single cry~tal on bo~h basal and prism planes, a SiC block, 8 piece of tungsten c~rbide, and a piece of talc.
':

Two CBN cylinders w~th attached metal alloy pad of the type de0cribed in ~xample 1 were made s~multaneously by u8ing ~n inert ~ep~rator of Na~19 which was in cont3ct w~th ~he metal alloy pad for each pellet. The cond~tions for ~ynthesis were 52.5 kb and 1450C applied for 45 minu~as. A metal alloy pad was found to be securely fa~ened to each abrasive~
contain~ng portion by thi~ proce~s.

, .

- , , .
: : ' '' 6 5. Z `

A mixture of metal snd HBN ~nd CBN was made and pre~sed into 3 separata cyllndler~ about 0.25l' in diam~ter. The mlxture compositiom was 0.240 gms CBN
0.060 gms HBN
O.4824 gm~ Fe (46 w/o~ :
9~336 gms ~i (32 w/o) 0.2208 gms Cr (21 w/o~
0.01053 gms Al (1 w¦o) The 3 pellets were placed (one above the other and in contact) in a high pressu~e cell and subjeeted to 55 kb and 1450C for 60 minutes. Upon removal from the cell the 3 pellets had 3intered together and had cemented the CBN grains ~both original and as prec~p~tated)to fonm a single cylinder 0~262" high and about 0O250ll in diameter. Metallogrsphic ex~mination of a poli~hed ~ection of thi~ specimen ~how~ good wetting of the CBN

grain30 ~ ~

Two grinding tool~ ~ith a central hole to -~.
facilits~e mounting were m~de ~multaneously ~n a high pressure cell by treatment for 60 minutes at 52.5 kb and 1450C. Two di~cs 0.140" high x 0.250" in diameter were 2S pressed from a powder mixture of HBN (0.140 gm), ~, , . . .. , ,, . , . . ., : . .

~Oti6S~2 RD~5823 Mn(0.170 gm~ Fe(0.114 gm) and Al(0.006 gm). A 1/8"
dia~eter hole W~8 then drilled through the eenter of each disc. In the high pressure cell these holes were filled with a 1/8" diame~er NaC1 plug~ and the two discs S were separated by a 0.030" salt d~sc. Two t'dough~ut-3haped" grinding tools consisting of CB~ in a metal matrix were produced. UQ ing the central hole these tools could be mounted directly on a shaft without ur~her pre-paration. In actual practice the initial disc3 could be pre3~ed out ln the final shape beore the hlgh pre~ure treatment rather than having to drill the central hole.

. .
The process of Example 4 was repeated exsept that the central hole was made 0.099" in diameter. Two annular grinding tool~ with sharp edges were s~multaneously :~`
prepared. One such tool wa~ taken as recovered from the high pressure~high temperature apparatus and was mounted on a shaft wi~hout add~tional preparat~on. ~he shaft W88 u~ed to aecommodate the tool in a ~mall rotating m~chine and a piece of tool steel ~as ground easily therewith.

A metal HBN mixture was made from powders taken in the following amounts:

: . . - - - - :
-. - .

.-~06G5~Z

0.200 gms HBN

0.0865 Fe .. ~ (8 w/o~ ~:

0.405 Ni ....... (43 w/o) :

0~505-Cr ....... (47 w/o) 0.0216 Al ...... (2 w/o3 . - :
., After mixlng, this material was divided into three ~pproxi- ~
mately equal port~ons and pressed into three disc~. These ~ ;
were placed in a high pressure cell and were ~eparated from each other with NaCl discs. After treatment at 55 kb and 1450C for 60 minutes, the discs were removed from the cell. Well-bonded CBN wa~ visible in each metal-B~7 disc, and the discs were suitable for mount~
for use as abrasive uni~8 a3 removed from the cell. The .
dimension of each metal-BN disc was 0.250" diameter x approximately .050" hi h.

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Claims (19)

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

1. The method of preparing cubic boron nitride abrasive tools comprising the steps of:
a) mixing HBN powder with a powdered metallic phase to produce a homogenous mixture, the atomic content of said metallic phase con-sisting essentially of aluminum atoms, atoms of a metal selected from the group consisting of chromium and manganese, and atoms of at least one metal selected from the group consisting of iron, cobalt and nickel, the weight per cent of HBN in said mixture, being in the range of from about 10 to about 50 weight percent;
b) pressing said mixture into some predetermined shape;
c) simultaneously subjecting said mixture to an operating temperature and operating pressure within the stability region of CBN defined by the use of the selected metallic phase and thereby forming a melt of the constituents of the metallic phase, the period of time of simultaneous temperature and pressure applic-ation being sufficient to permit disolution of all of the HBN in the metallic phase melt and the precipitation of CBN crystals therefrom;
d) cooling the resulting CBN/alloy system to about room temperature while maintaining the oper-ating pressure;
e) reducing the pressure to atmospheric pressure and;

f) recovering the preshaped abrasive body consisting essentially of CBN crystals distributed in a transition metal-aluminum alloy matrix.

2. The method of claim 1 wherein the metallic phase consists of iron, nickel, chromium and aluminum.

3. The method of claim 2 wherein the mixture contains from about 10 to about 22 weight percent HBN.

4. The method of claim 1 wherein the metallic phase consists of nickel, chromium and aluminum.

5. The method of claim 1 wherein the metallic phase consists of iron, manganese and aluminum.

6. The method of claim 5 wherein the mixture contains from about 15 to about 36 weight percent HBN.

7. The method of claim 1 wherein the metallic phase consists of nickel, manganese and aluminum.

8. The method of claim 7 wherein the mixture contains from about 16 to about 42 weight percent HBN.

9. The method of claim 1 wherein the metallic phase consists of iron-nickel-chromium-aluminum alloy containing 8 weight percent iron, 43 weight percent nickel, 47 weight percent chromium and 2 weight percent aluminum.

10. The method of claim 9 wherein the mixture contains about 42 weight percent HBN.

11. The method of claim 1 wherein the predetermined shape is annular.

12. The method of claim 3 wherein said metallic phase consists of 46 weight percent iron, 32 weight percent nickel, 21 weight percent chromium and 1 weight percent aluminum.

13. The method of claim 6 wherein said metallic phase consists of 39 weight percent iron, 59 weight percent manganese and 2 weight percent aluminum.

14. The method of claim 8 wherein said metallic phase consists of 39 weight percent nickel, 59 weight percent manganese and 2 weight percent aluminum.

15. A preshaped abrasive body comprising a matrix consisting essentially of aluminum, and an alloy of at least one metal selected from the group consisting of chromium and manganese, and at least one metal selected from the group consisting of iron, cobalt and nickel having small, uniform CBN
crystals distributed uniformly therein.

16. The abrasive body of claim 15 further comprising HBN.

17. The abrasive body of claim 16 wherein said HBN
and CBN together comprise about 10-50 weight percent of the total weight of said body.

18. The abrasive body of claim 15, 16 or 17 wherein said alloy has a composition intermediate the minimum composition at which extensive solid solution is obtained at the lowest temperature, and the eutectic composition of said alloy.

19. The abrasive body of claim 16 or 17 when prepared by the process of claim 1.