Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
RD-5823
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.
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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;
1066512 RD-5823
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-
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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
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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
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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;
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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.
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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. -
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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
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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
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~665~2
RD-5823
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 .
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~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.
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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
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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
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RD-5823
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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.
EXAMPLE 1
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 ;~
''` -''
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:~,
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14-
~3665~
RD-5823
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.
':
EXAMPLE 2
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.
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RD-5823
EXAMPLE 3
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 ~ ~
EXAMPLE 4
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),
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~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.
EXAMPLE 5
. .
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.
EXAMPLE 6
A metal HBN mixture was made from powders
taken in the following amounts:
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.-
~06G5~Z
RD-5823
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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