Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITE OF METAI~BONDED CUBIC BORON NITRIDE
AN~ A SUBSTRATE AND PROCESS OF PREPARATION
BACKGROUND OF THE INVENTION
This invention relate~ to the production ~f an article
comprising cubic boron nitride (CBN) particles cemented to each
other and bonded to a support l~yer, or substrate. Such com~
-posite articles find utility as wire drawing dies, tool inserts,-
abrasive bodies and wear surfaces. The preparation of the
substrate alone for use as a wear surface is also contemplated.
High temperature, ultra high pressure preparation of
tool inserts made of CBN crystals bonded to each other and
bonded to and supported on a sintered carbide mass is described
in U. S. Patent Nc. 3,743,489 - Wentorf et al. In the Wentor~
et al. patent, particular aluminum alloys are employed as the
bonding medium for the CBN crystals, not the substrate. The
preparatio~ of a metal-bonded CBN composite body containing
greater than 70 percent by volume C8N and prepared at pxessures
at which CBN is metastahle is disclosed in U. 5. Patent No.
3,982,911 - Lee. The method described in the Lee patent
requires placement of bonding matexi~l (i.e. certain aluminum
alloys) on the side of the CBN particulates opposite from the
substrate layer, an arrangement which presents a limitation on
the geometry of the final composite structure. For example,
it is very dif~icult to prepare a wire drawing die by the
methods in the Lee patent.
The aforementioned restriction on bonding material
placement has since been removed by the development of thé
process described in Canadian Appl-n. Ser. No. 394,637,
Lee et al., filed January 21, 1982, and assiqned to the
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assignee of the instant invention. The product produced
by the Lee et al. invention comprises a cemented diamond
mass bonded to a body of silicon-silicon carbide composite
material. The silicon-silicon carbide composite initially
serves as a source of silicon for the bonding, or cementing,
of the diamonds and subsequently provides for the structura'
stability of the article itself as its substrate.
DESCRIPTION OF THE INVENTION
In accordance with the inventive concept disclosed
herein, an integrated article comprising a mass of
cemented CBN particles bonded to a hard strong substrate
is produced by a process in which a quantity of multi-
component material comprising a ceramic and an aluminum-atom
yielding medium functions as the source of aluminum-base
bonding material for both the CBN particles and the
ceramic. Thus, aluminum-base material squeezed out of the
multi-component material by subjecting the system (i.e.
CBN and multi-component material) to sufficient pressure
while it is heated significantly above the melting point
of aluminum enters the mass of CBN particles to provide
the cementing medium for the CBN particles and the aluminum-
base material remaining serves as the bonding medium
for the ceramic with the cemented CBN mass being
affixed to the ceramic/aluminum-base substrate at the
same time.
The process aspect of this invention is conducted by
providing a quantity of CBN powder adjacent to the multi-
component material (i.e. substrate precursor) in a stabilized
geometry in a suitable container and subjecting this stabilized
geometry to the simultaneous application of a pressure of at
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least about two thousand pounds per square inch and heat to a
temperature above about 1200C in an inert atmosphere~ While
the melting point of aluminum is considerably below 1200C,
experimentation has shown that this much higher operating
temperature is necessary in order that the proper wetting angle
between the molten aluminum (or molten aluminum alloyJ and the
CBN surfaces can be secured. Conditioning of the aluminum-base
bonding material in this way to properly wet CBN surfaces is a
prerequisite to ob~aining suitable bonding between the.crystals
a~d betwee~ the crystals and the substrate.
The series of functions to be performed by the alumi-
num dictates that a certain minimum aluminum atom content be
present in the multi-component material at the initiation of
the process. Thus, once a determination has been made of the
size of the composite structure to be produced, i.e. the volume
of the sub~trate plus the volume of the abrasive layer, the
overall initial content of aluminum atom-yielding medium should
be equal to at least about 30 percent of the volume of the com-
posite structure to be prepared. The aluminum atom-yielding
medium may be present other than as pure aluminum, i.e. as an
alloy, providing there is at least 85 percent by weight of alumi-
num atoms in the alloy and the aluminum alloy is one which,when
molten, will wet CBN and is compatible with ceramic content of
the multi-component material. An amount of aluminum atom-yield-
ing medium of as much as about 60 volume percent of the completedcomposite structure may be used recognizing that of this quantity
only from about 30 to 35 percent of the volume of the completed
abrasive layer will be occupied by the aluminum-base bonding
medium. Too much aluminum in the substrate may result in a
reduction of desirable properties for certain uses. Thus, in
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the case of a tool insert the content of aluminum-base bonding
medium in the substrate should not exceed about 40 volume percent,
in the case of a bearing construction it is anticipated that as
much as 50 volume percent can be tolerated. As a practica~
matter, high volume percent contents ~e.g. 60 v/o~ of aluminum
atom-yielding medium would be used, when it is contemplated that
significant 10s9 of the medium will occur during conduct of the
process.
In the preferred embodiment, the multi-component
material consists of a ceramic powder and a source of aluminum
atoms. The ceramic powder should be compatible with the
aluminum source, pure or alloyed, such that any chemical
reaction occurring therebetween under the operating conditions
of the process will, at most, be slow enough such th~t the
ceramic particles will survive the process intact or suffer
very minor reduction in v~lume.
Upon completion of the process for making the
composite body, it will consist of a hard, relatively strong
su`bstrate to which is bonded a mass of cemented C3N particles.
The substrate itself, will consist of ceramic particles cemented
together with aluminum or with alumin~m plus an aluminum
intermetallic, depending upon the initial sourcP of th~ aluminum.
The aluminum content of the substrate may contain di~solved
material deri~ed from the ceramic or, in the-event an aluminum
alloy is employed, from alloy constituents.
Objects and the nature and advantages of the instant
invention will be apparent to ~hose skilled in ~he art from the
description set forth herein and the accompanying drawings.
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BRIEF DESCRIPTION OF THE DR~WINGS
The present invention will be readily and clearly
understood by those skilled in the art upon reviewing the
accompanying drawings in which:
Figure 1 represents a vertical sectional view of a
suitable containment of constituents to whi~h substantially
isostatic pressure is applied prior to forming a c~mp~ite
structure according to the inventive concept disclosed herein; -
Figure 2 is a view similar to Fig. 1 with the pressure-
transmitting medium, ~he containment and the constituents all
present in a stabilized geometry and transferred as such to a
graphite pressure die in which simultaneous heat and pressure
are applied thereto; and
Figure 3 represents a vertical sectionàl view through
one e~bodiment of the composite that can be produced by the
practice of this invention; in particular it represents the
composite structure produced from the constituents disposed in
the arrangement shown in Figs. 1 and 2.
MANNER AND PROCESS OF MA}CING AND USING THE INVENTION
Referring now more particularly to the drawings and
the following description, the reader may envision in Fig. 1
that in accordance with this invention a process for preparing
a composite structure is carried out by placing a.quantity of
fine, clean CBN crystals 10 and a mixture 12 of cer2mic
particles together with a powdered source of aluminum atoms
within a suitable metal container 14. The mass of CBN powder
should contain at least 70~ by volume CBN. Container 14, as
shown, consists of two interfitting cups 15, 16. Outer GUp 15
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is of refractory metal, such as molybdenum, for contaiNment and
inner cup 16, a lining for cup 15, is of a metal le.g. zirconium)
having gettering capabilities.
After the multi-component substrate precursor material
12 has been placed on top of the mass of fine CBN crystals 10,
initial containment may be completed by enclosing container 14
and the conten~s thereo with an inverted cup 18 of refractory
metal, which may be molybdenum, ~or example. In those instances
in which substrate precursor 12 is in the form of a eonsolidated,
close-fitting plug, cup 18 need not be used. This assembly is
packed in a mass of very fine particles 20 (preferably i~ the
size range from about 0.5 microns to about 20 microns) of a
pressure tr nsmitting medium ~preferably hexagonal boron
nitride) in a pressure mold 21 which comprises ring 22 and
pistons 23, 24. The mold components are preferably made of
tool steel. m e contents of pressure mold 21 is subjected to
pressures of greater than about Z0,000 psi, preferably about
100,000 psi, at room temperature (about 68-72F) to stabilize
the geometry thereof.
The powdered source of aluminum atoms may be aluminum,
p~r se, a preferred alloy of aluminum or aluminum plus a
separate quantity of an aluminum alloy. Manifestly, the molten
aluminumrbase metal, which is intended to enter the mass of CBN
and cement the particles together, should be chemically
compatible with CBN in that it will wet and bond thereto, but
not react extensively therewith. It is preferred that the CBN
crystals be significantly less than 20 microns in largest
dimension, although the range of particle sizes may, for sound
CBN c~ystals, extend even higher.
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The na~ure of the hexagonal boron nitride is su~h
that the fine particles will slip over each other and readjust
in an approximation of a hydrostatic action in response to the
uniaxially applied pressure to exert pressure over ~he en~ire
S surface of the ascembly. It is a~sumed that the applied
pressure is transmitted substantially undiminished to the
assembly.
The make-up of the multi-component precursor for the
substrate will employ ceramic particles in the 1-100~ range and
aluminum-atom yielding medium in the fonm of particles also in
the 1-100~ range. These materials, pxoperly mixed, may enter
this process either as a consolidated mass or as a mixed
p~wder.
When the geometry of the contents of pressure mold 21
has been stabilized by the pressure application described, it is
transferred as a packea mass from steel die or mold 21 to an
identical diameter graphite mold 30 shown in Fig. 2. Graphite
mold 30 comprises ring 31, pistons 32, 33, and a thermocouple
34, which enables monitoring of the temperature prevailing in
the dimensionally-stabilized a~sembly disposed between pistons
32, 33. The consolidated assembly including containex 14, CBN
crystals 10, the multi-component substrate precursor material
12, inverted cup 18, and pressure transmitting medium 20 i~
then simultaneously subjected (in a suitable furnace,-not
shown~ to elevated pressure, preferably about 10,000-12~000
pounds per square inch between pistons 32, 33 and to a tempera-
ture in the range of from about 1200C to about 1400C for from
about five to eight minutes. After the heater is shut off, the
die is kept under pressure until it has cooled significantly
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bel~w the melting temperature of the aluminum atom sourre.
Thereafter, the assembly is removed.
The heating-pressurizing step is conducted in an
atmosphere of nitrogen, hydrogen or an inert gas. During the
period of time in which this step is conducted, the po~dered
metal source of aluminum atoms is melted, raised to a tempera-
ture at which it will satisfactorily wet CBN and squeezed from
mixture 12 so that it can infiltrate the interspaces of CBN
mas~ 10. Assuming the asembly does not leak, the rest of the
powdered source of aluminum atoms remains in layer 12 to cover
- the ceramic particles and function as the cementing medium
therefor. Among these ceramic materials suitable for use in
this invention and able to employ aluminum or alumin~m alloys
as the cementing medium to form a strong, hard compo ition are
silicon carbide; silicon nitride; the carbides, nitrides and
borides of titanium, hafnium, zirconium, vanadium, niobium,
tantalum, molybclenum and tungsten, and mixtures of the fore-
going. Preferred ceramic materials are titanium diboride,
tungsten carbide (more expensive and not as stable as tit~nium
diboride), silicon nitride and silicon carbide.
Although eventually the heat and pressure must be
simultaneously applied to container 14 and its contents, it
may be of advantage, d~pending upon the source of alumlnum
employed, to apply heat before the application of pressure or
to apply pressure before the initiation of the heating
operation.
After completion of the simultaneouc heat/pressure
operation, the assembly (i.~. container 14 and its contents)
is removed from the system, cleaned and a composite body is
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recovered. For the arrangement of materials described herein,
by way of example, such a composite body is ~hown in Fig. 3.
Similarly, an article useful a~ a blank for the operation of
a wire drawing die can be prepared using the appropriate
arrangement of material~ described in aforementioned Ser. No.
394,637..
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The composite structure shown in ~ig. 3 comprises a
mass 40 of cemented CBN, which ma~ is affixed to the stiff
~upport material constituting sub~trate 41. Substrate 41
consi~ts essentially of ceramic particles together with the
c2menting medium therefor, which cementinq medium comprises
either aluminum containinq dissolved material derived from the
ceramic constituent and/or an aluminum intermetallic depending
on the starting source of aluminum atoms.
Practice of the aspect of this invention-productive
of the CBN~substrate composite has required the development of
new substrate compositions; namely, compositions in which
ceramic particles are cemented, i.e. bonded, together by a
medium very high in aluminum atom co~tent.
The following examples set forth experiments
illustrating the results obtained in the practice of the
invention as descxibed herein; in an analo~ous process using
other than a ~our~e of aluminum, and i~ an analogous process
using diamond crystals in place of CBN. Abbreviations in the
examples are explained as follows: weight percent (w/o);
volume percent (v/o); pounds per s~uare inch (psi); thousand
pounds per square inch (kpsi); surface feet per minute (SFPM);
micrometer (~); hexagonal boron nitride (HBN); milligram (mg);
Rockwell (Rc); l/lO00 inch (mil). Where abbreviations used for
the elements are set forth, standard designations are employed.
E _
About 150 mg of jet milled CBN powder (4-8~ size) was
packed in a zirconium cup with an additional zirconium strip
in~erted around the edge of the cup. A mixture of 200 mesh
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silicon carbide powder (60 w/o) and 100 mesh aluminum powder
(40 w/o; ~44 v/o) weighing 385 mg was packed directly on top of
the CBN powder. A hot pressed HBN disc tightly fitting in the
cup was inserted to cover the packed powder. The entire assem-
bly was then packed with HBN powder in a cemented carbide-
lined steel die and the mass was pressed up to lOQ,000 psi.
The pressed ~i.e. stabilized) mass was then transferxed into a
graphite die for hot pressing. ~he hot pressing conditions
.
were 6 minutes under 8,000 psi at 1300C in a nitrogen atmos-
phere. It took 4 minutes for the induction heater to bring
the die temDerature u~ to the process temperature, and the die
was kept under pressure at the end of the pressing cycle until
the die was cooled sufficiently below the meltingb~mperature
of the binder.
The CBN layer of the recovered sample was thoroughly
infiltrated with the aluminum-base binder metal and remained
bonded strongly to the aluminum~silicon carbide composite
substrate.
ExAMæLE 2
Two samples were processed simultaneously in this
example. A first zirconium can was packed with 150 mg of the
same CBN powder as in Example 1, while a second zirconium can
was packed with 300 mg of 325/400 mesh CBN powder. Both cans
were then filled with 50 w/o silicon nitride (-325 mesh) and
50 w/o aluminum (100 mesh) as a mixture. Both cans were
processed for hot pressing according to the steps set forth
in Example 1.
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8055
Both the fine CBN powder as well as the more coarse
CBN samples were completely infiltrated by the aluminum-base
binder a~d each formed an inte~ral body of C~N bonded on the
aluminum~bonded silicon nitride substrate.
EX~MPLE 3
In this example, a mixture of 85 w/o of silicon
carbide and lS w/o (~17 v/o) aluminum was evaluated as the
substrate composition. The same CBN powder as the one in
Example 1 was also used for this case and the same steps were
conducted as in Example 1. The result showed no sign of metal
infiltration and the CBN layer remRined powdery~ illustrating
that the aluminum atom-yielding medium was present in too ~mall
an ~mount.
EXAMPLE 4
A jet milled CBN powder of 4-8~ size was placed in a
molybdenum can having a zirconium liner in contact with a
substrate material comprising a mixture of 70 w/o of Ti82~
25 w/o of Al, and 5 w/o of NiA13. The substrate material had
previously been pressed in a cylindrical die under 12,000 psi
to form a pill-shaped body.
The open end of the molybdenum can was then covered
with another molybdenum can. The two molybdenum cans were not
fastened to each other but could freely slide with respect to
each other.
The cell assembled in this way was packed in a fine
grain size HBN powder in a steel die and pressed to about 95
kpsi at room temperature (^~68-72~) to stabilize the geometry.
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The HBN pa~ked cell was then inserted into a graphite die and
simultaneously pressed and heated (at 12 kpsi and at 1360C)
for about 6 minutes. Infiltration of the CBN ma~s by binder
material from the substrate was excellent and a very good
composite was formed with the CBN layer cemented to the TiB2
substrate with`its aluminum-base cementinq medium.
EXAMPLE S
A quantity of mixed grain size (80 w/o of 4-8~ and
20 w/o of -2~) CBN powder was placed in a zirconium-lined
molybdenum can in contact with a pressed pill of substrate
material compri~ing a mixture of 70 w/o of TiB2~ 25 w/o of Al,
and 5 w/o of NiA13, the pill being pxepared as in Example 4.
The open end of the first molybdenum can was then
covered with a second (i~e. inverted) molybdenum can. The two
molybdenum cans were not attac~ed to each other, but could
freely slide with respect to each other.
The cell assembled in this way was packed in a fine
grain size HBN powder in a die and pressed to about 95 kpsi at
room temperature to stabilize the geometry. The stabilized
assembly packed in HBN was then inserted into a graphite die
and simultaneously pressed and heated (at 12 kpsi and at 1360C~
for about 6 minutes. Infiltration of the CBN mass by aluminum-
base binder material from ~he substrate was again excellent,
as in Example 4, and a very good compact was also formed with
the CBN layer cemented on the TiB2 substrate.
EXAMPLE 6
About 150 mg of CBN powder with an average particle
size of about 7~ was packed into a Mo cup having a zirconium
117726Z R~-8055
liner. A cemented tungsten carbide disc (87 w/o WC and
13 w/o Co~ of 125 mil thickness was placed on top of the CBN
powder. The cup assembly was then packed in H~ powder and
the whole charge was pressed to about 100 kpsi. The pressed
assembly was loaded into a graDhite mold and heated to 1350C.
The assembly was kept at this temPerature for 8 minutes. A
constant pressure of 10 kpsi was maintained throughout the
heating and cooling cycle until the mold had cooled suffi-
ciently. Since the cemented carbide disc effectively sealed
the assembly, no inverted Mo cup was used.
The final compact showed that the cobalt binder from
the substrate cemented carbide had infiltrated into the CBN
pGwder. However, the resultiny compact did not possess
adequa~e strength, because cobalt did not bond strongly to the
CBN r
EXAMPLE 7
400 mg of Grade 45 (30-60~ diamond powder was packed
at the bottom of a zirconium cup, and a mixture of 50 w/o
tungsten carbide (average 5~), 32.4 w/o silver, 12.5 w/o copper,
and 5 w/o titanium was placed on top of the diamond powder to
fill the cup. The can was then processed through the same
procedures as in Example 1. However, the sample was h~ated to
the hot pressing temperature (1300C) before the pressure was
applied to ensure proper alloying of the infiltrant.
The diamond layer of the recovered sample was not
infiltrated by the metallic medium in the tungsten car~ide/
metal mixture.
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EXAMPLE 8
The coarser diamond powder (140/170 mesh) than the
powder used for Example 7 was used in this example to evaluate
~he effect of diamond particle size on the infiltration process.
In addition, a second assembly using diamond (140/170 mesh) and
10 w/o zirconium powder as a mixture in place of pure diamond
was also processed simultaneously with the first can. Other
process steps were the same as in Example 7.
The first sample containing diamond alone was
infiltrated with metallic bindex from the substrate, but
diamond particles in the iniltrated layer pulled out rat~er
easily during polishing, indicating that the diamond-to-metal
bond ~trength in the diamond layer was not good. The second
sample containing zirconium in the diamond layer was not
infiltrated at a~l by the alloy from the substrate powder.
EXAMPLE 9
Grade 45 diamond powder (30-60~) was used in this
example in two assemblies. Powder mixture used for the source
of binder for the diamond layer as well as the proposed
substrate was 60 w/o TiC (approx. 2~ size) and 40 w~o Si for
the first assembly and 60 w/o WC (approx. 5~) and 40 w/o Si for
the second assembly. The hot pressing temperature for this
example was 1550C and the rest of the process steps were the
same as in Example 7.
Silicon in the carbide layer did not infiltrate into
the diamond layer in either case.
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EXAMPLE 10
In this example, a mixture of 75 w/o of tungsten
carbide with average particle size of 5~ and 25 w/o ~65.7 v/o)
o~ 100 U. S. mesh size aluminum was evaluated as the multi-
S component substrate precursor composition. The CBN powder andother process steps were the same as in Example 1. The results
were that the CBN layer was infiltrated thoroughly,but the
excesæ aluminum in the subs~rate caused severe cracking along
the CBN layer-substrate interface.
EXAMPLE 11
Example 10 was repeated with a mixture of 85 w/o
tungsten carbide and 15 w/o (50.4 v/o) aluminum as the multi-
component substrate precursor composition. Again the CB~ layer
was infiltrated thoroughly, but miS time this bonded layer was
securely bonded to the aluminum~bonded tungsten carbide
substrate body.
From the foregoing examples, it may be understood
that a mass of metal~bonded CBN and a meta~-bonded substrate
can be simultaneously prepared with the CBN mas affixed to the
substrate by a process in which molten aluminum-base material is
caused to leave the substrate precursor and enter the parti-
cuiate CBN to effect the bonding thereof. various multi-
component substrate precursor materials have been mentioned
hereinabove as being suitable in combination, preferred ceramic
components include titanium diboride, tungsten carbide, silicon
nitride and silicon carbide, while suitable binders include
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aluminum and very high aluminum content (i.e. at least about
85 w/o) aluminum alloys. A preferred aluminum alloy contains
aluminum accompanied by a strengthening element such as nickel.
It will be o~vious to those skilled in the art that
various changes may be made without departing from the scope
of the invention as disclosed herein in its best mode and the
invention is not to be considered limited to what is shown in
the drawings and described in the specification.
