Note: Descriptions are shown in the official language in which they were submitted.
: ~ :. 3 ~ ~i t,
~9 3-643 -1-
CE~A~IC-METAL ARTICLES ~ND MET~ODS OE MANUFACT~RE
This invention relates to metal bonded ceramic, e.g.
carbide, nitride, and carbonitride, articles for use as
cutting tools, wear parts, and the like. In particular
the invention relates to such articles bonded with a
binder including both nickel and aluminum and methods for
producing such articles.
The discovery and implementation of cobalt bonded
10 tungsten carbide (WC-Co) as a tool material for cutting
metal greatly extended the range of applications beyond
that of conventional tool steels. Over the last 50 years
process and compositional modifications to WC-Co materials
have led to further benefits in wear resistance, yet the
potential of these materials is inherently limited by the
physical properti.es of the cobalt binder phase. This
becomes evident when cutting speeds are increased to a
level which generates sufficient heat to soften the metal
binder. The high speed finishing of steel rolls serves as
20 an example of a metal cutting application where the tool
insert must maintain its cutting edge geometry at high
temperature and resist both wear and deformation.
Unfortunately, the wear characteristics of WC-Co based
cemented carbides are also affected by the high
temperature chemical interaction at the interface between
the ferrous alloy workpiece and the cemented carbide tool
surface. Additions of cubic carbides (i.e. TiC) to the
WC-Co system have led to some improvement in tool
performance during steel machining, due in part to the
30 resulting increased hardness and increased resistance to
chemical interaction. However, the performance of such
TiC-rich WC-Co alloys is influenced by the low fracture
toughness of the TiC phase, which can lead to a tendency
toward fracture during machining operations involving
intermittent cutting, for example milling.
89-3-643 -2-
Accordingly, a cemented carbide material suitable for
cutting tools capable of withstanding the demands of hard
steel turning (wear resistance) and steel milling (impact
resistance) would be of great value. Such a new and
improved material is described herein.
According to one aspect of the invention, there is
provided a ceramic-metal article comprising: about 80-95%
by volume of a granular hard phase consisting essentially
lO of a ceramic material selec-ted from the group consisting
of the hard rafractory carbides, nitrides, carbonitrides,
oxycarbides, oxynitrides, carboxynitrides, and mixtures
thereof of a cubic solid solution selected from the group
consisting of zirconium-titanium, hafnium-titanium,
hafnium-zirconium, vanadium titanium, niobium-titanium,
tantalum-titanium, molybdenum titanium, tungsten-titanium,
tungsten-hafnium, tungsten-niobium, and tungsten-tantalum;
and about 5-20% by volume of a metal phase, wherein said
metal phase consists essentially of a combination of
20 nickel and aluminum having a ratio of nickel to aluminum
of from about 90:10 to about 70:30 by weight and 0-5% by
weight of an additive selected from the group consisting
of titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum, tungsten, cobalt, boron,
carbon, and combinations thereof; wherein said article has
a density of at least about 95% of theoretical.
More specifically we provide an article in accordance
wherein said metal phase consists essentially of a Ni3Al
30 ordered crystal structure or of a Ni3Al ordered crystal
structure coexistent with or modified by said additive.
According to another aspect of the invention, there is
provided a process for producing a ceramic-metal article
comprisin~ the steps of: presintering, in a vacuum or
inert atmosphere at about 1475-1675C and for a time
89-3-643 -3-
sufficient to permit developmant of a microstructure with
closed porosity, a mixture of about 80-95% by ~011lme of a
granular hard phase component consisting essentially of a
ceramic material selected from the group consisting of (a)
the hard refractory carbides, nitrides, carbonitrides,
o~ycarbides, oxynitrides, carboxynitrides, borides, and
mixtures thereof of the elements selected from the group
consisting of titanium, zirconium, hafnium, vanadium,
niobium, tantalum, chromium, molybdenum, tungsten, and
lO boron, and (b) the hard refractory carbides, nitrides,
carbonitrides, oxycarbides, oxynitrides, and carboxy-
nitrides, and mixtures thereof of a cubic solid solution
selected from the group consisting of zirconium-titanium,
hafnium-titanium, hafnium-zirconium, vanadium-titanium,
niobium-titanium, tantalum-titanium, molybdenum-titanium,
tungsten- titanium, tungsten-hafnium, tungsten-niobium,
and tungsten-tantalum; and about 5-20% by volume of a
metal phase component, wherein said metal phase component
consists essentially of nickel and aluminum, in a ratio of
20 nickel to aluminum of from about 85:15 to about 88:12 by
weight, and 0-5% ~y weight of an additive selected from
the group consisting of titanium, zirconium, hafnium,
vanadium, niobium, tantalum, chromium, mol~bdenum,
tungsten, cobalt, boron, carbon, and combinations thereof;
and densifying said presintered mixture by hot isostatic
pressing at a temperature of about 1575-1675C, in an
inert atmosphere, and at about 34~207 MPa pressure for a
time sufficient to produce an article having a density o
at least about 95% of theoretical.
More specifically we provide a process wherein said
presintering step is carried out at about 1475-1575C and
said presintering step is carried out at a temperature at
least 50C lower than that of said densifying step.
89-3-643 -4-
Also, more specifically, we provide a process wherein
said ratio of nickel to aluminum is selected such that
during said densifying step said metal phase component is
substantially converted to a Ni3Al ordered crystal
structure or a Ni3Al ordered crystal structure coexistent
with or modified by said additive.
Some embodiments of the invention will now be
described, by way o~ example, with reference to the
accompanying drawings in which:
FIG. 1 is a graphical representation comparing the ma-
chining performance of a cutting tool shaped article
according to one aspect of the invention and commercially
available tools;
FIG. 2 is a graphical representation comparing the
milling performance of cutting tool shaped articles
according to two aspects of the invention and commercially
available tools;
FIGS. 3-6 are photomicrographs illustrating wear
characteristics of various tools of related compositions,
20 including one tool according- to one aspect of the
invention.
Described herein as exemplary ceramic materials are
those including one or more hard refractory carbides,
nitrides, oxycarbides, oxynitrides, carbonitrides,
carboxynitrides, or borides of a tungsten-titanium solid
solution, or one or more hard refractory carbides,
nitrides, oxycarbides, oxynitrides, carbonitrides, or
carboxynitrides of tungsten, bonded by an intermetallic
binder combining nickel and aluminum. These exemplary
30 materials are considered typical o~ those claimed, and the
following description thereof is not intended to limit the
invention as recited in the claims.
A typical densified, metal bonded hard ceramic body or
article is prepared from a powder mixture including cubic
solid solution powders as the hard phase component, and a
combination of both Mi and Al powders in an amount of
J
89-3-643 -5-
about 5~20yO by volume as the binder component. Typical
solid solution powders include (WX,Til~x3C, (WX,Til_x)N,
(~x,Til_x)(C,N), (Wx,Til_x)(O,C~, (Wx,Til_x~(O,N),
(WX,Til x)(O,C,N), or combinations thereof. Most
preferably, x is a weight fraction o about 0.3 0.7. The
best combination of properties (hardness and fracture
toughness) is obtained when total metal binder addition is
in the range of about 7-15% by volume. For best results
in sintering and in both physical and chemical property
lO balance, the weight ratio in the solid solution hard phase
of tungsten to titanium should be in the range of about
0.3-3.0 and more preferably about 0.6-1.5. Materials with
a W:Ti ratio lower than about 0.3 exhibit lowered fracture
toughnass and impact resistance, which can be important in
some applications, e.g. when used as cutting tools for
steel milling. A ratio of about 3.0 or less can enhance
wear resistance, which can also be important in some
applications, e.g. when used as cutting tools for steel
turning.
Alternatively, the ceramic materials may typically
include compounds of titanium, zirconium, hafnium,
vanadium, niobium, tantalum, chromium, molybdenum,
tungsten, boron, or mixtures thereof. Typical of these
hard phase components are TiC, HfC, VC, TaC, Mo2C, WC,
B4C, TiN, Ti(C,N), TiB2, or WB. The powder mixture
contains the hard phase component, for example a tungstan
carbide powder, and a combination of both Ni powder and Al
powder in an amount of about 5-20% by volume as the metal
component. The best combination of properties ~hardness
30 and fracture toughness) is obtained when total metallic
phase addition is in the range of about 7-15% by volume.
In this exemplary material, the tungsten carbide ceramic
component provides excellent wear resistance, which is
important in applications such as cutting tools for steel
turning. The metallic phase provides greater fracture
toughness for the material than the sintered ceramic
! ~ ?
89-3 643 -6-
material alone, and the metallic phase combining aluminum
and nickel in the above ratios provides improved high
temperature properties such as creep resistance over
cobalt or other single metal.
In any of these materials, as stated above, the metal
powder component represents about 5-20% by volume and
preferably about 7-15% by volume of the total starting
formulation. The binder metal powder includes nickel in
an amount of about 85-88% by weight, and aluminum in an
lO amount of about 12-15% by weight, both relative to the
total weight of the binder metal powder. A minor amount
of titanium, zirconium, hafnium, vanadium, niobium,
tantalum, chromium, molybdenum, tungsten, cobalt, boron
and/or carbon, not to exceed about 5% by weight of total
binder metal, may also be included. The preferred
composition is 12-14% by weight Al, balance Ni. In the
most preferred binder compositions the Ni:Al ratio results
in the formation o~ a substantially Ni3Al binder, having
the Ni~Al ordered crystal structure. The amount of Ni3Al
20 is also dependent on the processing, e.g. the processing
temperatures, and may be selectecl to achieve various
properties in the cermet, e.g. 100%, 40-80%, less than
50%, etc. of the metal phase. The ratio of Ni:Al powders
required to achieve the desired amount of Ni3Al may be
readily determined by empirical methods. Alternatively,
prereacted Ni3Al may be used in the starting formulation.
In some compositions, this ordered crystal structure
may coexist or be modified by the above-mentioned
additives. The preferred average grain size of the hard
30 phase in a densi~ied body of this material for cutting
tool use is about 0.5-5.0 ~m. In other articles for
applications where deformation resistance requirements are
lower, e.g. sand blasting nozzles, a larger range of grain
sizes, e.g. about 0.5-20 ~m, may prove satisfactory. The
material may be densified by known methods, for example
,1, . ' I C ~
89-3-~43 -7-
sintering, continuous cycle sinterhip, two step
sinter-plus-HIP, or hot pressing, all known in the art.
An alternate densified, metal bonded hard ceramic body
or article has the same overall composition as those
described above, but differs in that it exhibits a
gradat~d hardness, most preferably exhibiting lower
hardness in the center portion of the body and
progressively increasing hardness toward the tool surface.
To obtain a body with these characteristics, the
10 densification process includes a presintering step in
which the starting powder mixture is subjected to
temperatures of about 1475-1575C, preferably
1475-1550C, in vacuum (e.g. about 0.1 Torr) or in an
inert atmosphere (e.g. at about 1 atm) for a time
sufficient to develop a microstructure with closed
porosity, e.g. about 0.5-2 hr. As used herein, the term
"microstructure with closed porosity" is intended to mean
a microstructure in which the remaining pores are no
longer interconnected. Subsequently, the body is fully
20 densified in an inert atmospheric overpressure of about
34-207 MPa and temperature of about 1575-1675C,
preferably 1600-1675C, for a time sufficient to achieve
full density, e.g. about 0.5-2 hr. The presintering
temperature is at least 50C lower than the ~inal
densification temperature. These gradated bodies exhibit
outstanding impact resistance, and are particularly useful
as milling tool inserts and as tools for interrupted
cutting of steel.
The depth to which the gradated hardness is effected
30 is dependent on the presintering temperature. Thus, if a
fully gradated hardness is not critical a similar process,
but with a broader range of presintering temperatures,
about 1475-1575C, may be used, and a 50C difference
between the presintering and hot pressing temperatures is
not required.
s
89-3-643 -8-
For certain applications such as cutting -tools the
articles described herein may be coated with refractory
materials to provide certain desired surface
characteristics. The preferred coatings have one or more
adherent, compositionally distinct layers of refractory
msotal carbides, nitrides, and/or carbonitrides, e.g. of
titanium, tantalum, or hafnium, or oxides, e.g. of
aluminum or zirconium, or combinations of these materials
as different layers and/or solid solutions. Such coatings
may be deposited by methods such as chemical vapor
deposition (CVD~ or physical vapor deposition (PVD), and
preferably to a total thickness of about 0.5-lO ~m. CVD
or PVD techni~ues known in the art to be suitable for
coating cemented carbides are preferred for coating the
articles described herein.
Coatings of alumina, titanium carbide, titanium
nitride, titanium carbonitride, hafnium carbide, hafnium
nitride, or hafnium carbonitride are typically applied by
CVD. The other coatings described above may be applied
either by CVD techniques, where such techniques are
applicable, or by PVD techniques. Suitable PVD techniques
include but are not limited to direct evaporation and
sputtering. ~lternatively, a refractory metal or
precursor material may be deposited on the above-described
bodies by chemical or physical deposition techniques and
subsequently nitrided and/or carburized to produce a
refractory metal carbide, carbonitride, or nitride
coating. Useul characteristics of the preferred ~VD
method are the purity of the deposited coating and the
en~lanced layer adherency often produced by diffusional
interaction between the layer being deposited and the
substrate or intermediate adherent coating layer during
the early stages of the deposition process.
For certain applications, for example cutting tools,
combinations of the various coatings described above may
be tailored to enhance the overall performance, the
89-3-643 ~9-
combination selected depending, for cutting tools, on the
machining application and the workpiece material. This is
achieved, for example, through selection of coating
combinations which improve adherence of coating to
substrate and coating to coating, as well as through
improvement of microstructurally influenced properties of
the substrate body. Such properties include hardness,
fracture toughness, impact resistance, and chemical
inertness of the substrate body.
The following Examples are presented to enable those
skilled in the art to more clearly understand and practice
the present invention. These Examples should not be
considered as a limitation upon the scope of the present
invention, but merely as being illustrative and
representative thereof.
EXAMPLES
Cutting tools were prepared from a powder mixture of
10% by volume metal binder (86.7% Ni, 13.3% Al, both by
20 weight, corresponding to a Ni3Al stoichiometric ratio) and
90% by volume hard phase ~either a non-solid solution
carbide or boride, or a (W,Ti)C in a 50:50 ratio by weight
solid solution W:Ti).
~XAMPLE 1
A charge of 111.52 g of the (W,Ti)C and metal powder
mixture, 0.0315 g of carbon, 4.13 g of paraffin, and 150
cc of heptane was milled in a 500 cc capacity tungsten
carbide attritor mill using 2000 g of 3.2 mm cemented
30 tungsten carbide ball media for 2~ hr at 120 rpm. After
milling, the powder was separated from the milling media
by washing with additional heptane through a stainless
steel screen. The excess heptane was slowly evaporated.
To prevent binder (wax) inhomogeneity, the thickened
slurry was mixed continuously during evaporation, and the
caking powder broken up with a plastic spatula into small,
'. ~ ! j
89-3-643 -10-
dry granules. The dry granules were then sieved in two
steps using 40~ and 80-mesh screens. The screened powder
was then pressed at 138 MPa, producing green co~pacts
measuring 16 x 16 x 6.6 mm and containing 50-60% by volume
o solids loading.
The pressed compacts were placed in a graphite boat,
covered with alumina sand, and placed in a hydrogen
furnace at room temperature. The temperature then was
raised in increments of 100 every hour and held at 300C
10 for 2 hr to complete the removal of the organic binder.
The dewaxed samples were then taken from the hot zone,
cooled to room temperature, and removed from the hydrogen
furnace.
The dewaxed samples were then densified in two steps:
presintering and hot isostatic pressing (HIPing). The
dewaxed compacts, on graphite plates which had been
sprinkled with coarse alumina sand, were presintered at
1650C for 1 hr at about 0.1 Torr in a cold wall graphite
vacuum furnace. The initial rise in temperature was
20 rapid, 15C/min up to 800C. From 800C the rise was
reduced to 4.5C~min, allowing the sample to outgas.
Throughout the entire presintering cycle, the chamber
pressure was maintained at about 0.1 Torr.
The final consolidation was carried out in a HIP unit
at 1650C and 207 MPa of argon for 1 hr, using a heating
rate of about 10C/min. The maximum temperature (1650C)
and pressure (207 MPa) were reached at the same time and
were maintained for about 1 hr, followed by oven cooling
to room temperature. Cutting tools prepared by this
30 process exhibited improved performance over that of
commercially available cutting tools in machining of
steel, as shown in FIG. 1. The tools were used in the dry
turning of 1045 steel, 600 ft/min, 0.016 in/rev, 0.050 in
D.O.C. (depkh of cut). The wear values shown in FIG. 1
are averages of the wear induced at three corners;
29 1 in3 of metal were removed. As may be seen in FIG. 1,
89-3-643
the tool of this Example compared avorably in turning
performance with commercial tool #1, showing significantly
superior notch wear, and was far superior to commercial
tool #2. The composition and room temperature hardness of
the commercial materials of FIG. 1 and of the tools of
this Example are compared in Table 1 below.
EXAMPLE 2
The cutting tools of this Example were prepared as de-
10 scribed above for Example 1, except that the dewaxedcompacts were presintered at 1500C for 1 hr. at 0.1 Torr
in the same cold wall graphite vacuum furnace. The rise
in temperature was the same as in Example 1: initially
rapid, 15C/min. up to 800C. From 800C, the rise was
reduced to 4.5C/min., allowing the sample to outgas.
The metal bonded carbide cutting tool of Example 2 was
characterized by a specific microstructure in which a
gradient of hardness ~as shown in Table 1) and fracture
toughness was developed from the surface of the densified
article to its core. The performance of the gradated
cutting tool material was measured by machining tests, the
results of which are shown in FIG. 2. The impact
resistances of the tool of khis Example (with gradated
hardness), the kool of Example 1 (without gradated
hardness), and two commercial grade tools were determined
by a dry flycutter milling test on a steel workpiece
(Rockwell hardness, Rc = 24) using a standard milling
cutter (available from GTE Valenite Corporation, Troy, MI,
U.S.A.) at 750 ft/min, 4.2 in/rev, 0.125 in D.O.C. The
wear values shown in FIG. 2 are four corner averages at
341 impacts per corner. The specific cutting tools used
in the machining tests are listed in Table 1 with their
compositions and room temperature hardness.
As shown in FIG. 2, the tool of this Example was
superior in milling performance to both commercial tools.
Further, although the tool of Example 2 was mosk suitable
89-3 643 -12-
for this application, the tool of Example 1 also proved to
have commercial value for such high impact machining.
TABLE 1
Hardness*, Hardness*,
SampleCompositionKnoop, GPa Vickers, GPa
Example(W,Ti)C +15.4 + 0.3 13.8 + 0.3
110 v/o (Ni ~ Al)
Example(W,Ti)C +Gradated** -
210 v/o (Ni -~ Al)core: 18.10
surface: 20.34
Commer- TiC 14.5 + 0.2 16.53 + 0.16
cial10 Ni + 10 Mo (v/o)
Tool #l
Commer-10 Co + 10 Ni13.4 + 0.2
cial+ 80 other~ (v/o)
Tool #2
* l.ON load.
** 0.5N load.
~ MoC, TiC, TiN, VC, WC (proprietary composition)
EXAMPLES 3-6
Cutting tools were prepared as described above for
Examples 1 and 2, using the same hard phase/metal phase
powder ratio, but were presintered and some of them hot
isostatically pressed at the temperatures and for the
times shown in Table 2. The rise in temperature was the
same as in Example 1: initially rapid, 15C/min. up to
30 800C. From 800C, the rise was reduced to 4.5C/min.
Characterization by X-ray diffraction determined that the
compacts evidenced varying amounts of ~' crystal ~tructure
Ni7Al formation in their metal phases.
, `, . S,;3 .'.,
8 9- 3 - 6 ~ 3 - 13 -
TABLE 2
Sinter Sinter HIP HIP
Fx.Composition Temp., C Time, hrTemp., C Time, hr
-
3CW,TI)C +
10 v/o Ni-Al1650 1 1650
4CW, Ti )C ~
10 v/o Ni-Al1550 1 1650
10 5(W,Ti~C ~
10 v/o Ni-Al1650
6(W,Ti)C +
10 v/o Ni-Al1500 1 -- --
8g-3-643 -14-
EXAMPLES 7-lO
Ceramic-metal cutting tools with a nickel and aluminum
metal phase were prepared as described above for
Example 1, except that the compositions were as shown in
Table 3. Th0 performance of the cubic solid solution
(W,Ti)C-based ceramic-metal cutting tools was compared to
that of similar tools not containing solid solution
carbide in the dry -turnlng of 1045 steel, 475 ft/min,
0.012 in/rev, 0.050 in D.O.C. (depth of cut).
TABLE 3
Nose FlanX Crater Metal
Ex. Composition Wear, Wear, Wear, Removed,
in in in in3
-
7 WC ~ Tool
10 v/o Ni-Al -- -- -- failed
8 TiC +
20 10 v/o Ni-Al 0.0090.006<0.001 70
9Mixture
WC ~ TiC* +
10 v/o Ni-Al 0.00750.0070.004 64.8
10Solid soln.
(W,Ti)C*
10 v/o Ni-Al 0.0080.0035<0.001 70
* W:Ti = 50:50 by weight.
The wear values shown in Table 3 are averages of the
30 wear induced at three corners during extended cutting
tests. The WC-based cermet tool failed before the
extended cutting tests were completed. About 65-70 in3 of
metal were removed in the remaining tests. As shown in
Table 3, the titanium carbide-based cermet tool was
superior in extended wear performance to the similar
89-3-643 -15-
tungsten carbide-based tool (which failed before the
extended cutting test was completed), and surpassed the
crater wear performance of a similar tool based on a
mixture of tungsten carbide and ti-tanium carbide.
The tool of Example 10 was similar in every way to
those of Examples 7, 8, and 9, except that it included a
cubic solid solution carbide of tungsten and titanium.
The tools of Examples 9 and 10 were actually of an
identical chemical composition, both including tungsten
lO and titanium in a 50:50 weight ratio. Surprisingly,
however, it was found that this solid solution
carbide-containing tool outperformed the WC-based tool and
even the (TiC + WC)-based tool in the machining tests.
The solid solution carbide-based tool also showed superior
flank wear performance and equivalent crater wear
performance to the presumably harder TiC-based tool of --
Example 8.
The surprising superiority of the cubic solid solution
carbide-based tool may be clearly seen in FIGS. 3-6, which
20 are photomicrographs of the wear induced at one corner of
each of the tools listed in Table 3 af-ter 20 in3 of metal
removal. As illustrated in FIG. 3, the tungsten
carbide-based tool exhibits the severe cratering which
ultimately led to failure of the tool. FIG. 4 illustrates
the severe nose deformation o the titanium carbide-based
tool; this tool, however, exhibits essentially no
cratering. In FIG. 5 is illustrated the effect of
combining the cratering resistance of titanium carbide
with the resistance to nose deformation of tungsten
30 carbide in the (WC ~ TiC~-based tool: the tool exhibits
little deformation and only slight cratering. The
superiority of the tool in accordance with one aspect of
the invention, the solid solution carbide-based tool of
Example 7 is illustrated in FIG. 6, in which the tool
exhibits essentially no cratering and far less deformation
and wear than any of the similar tools.
89-3-643 -16-
~XAMPLES 11~16
Ceramic-metal compacts were prepared from a powder
mixture of 10% by volume metal phase (86.7% Ni, 13.3% Al,
both by weight, corresponding to a Ni3Al stoichiometric
ratio) and 90% by volume ceramic hard phase.
A charge of 221.28 g of the tungsten carbide and metal
powder mixture, 0.0315 g of carbon, 4.13 g of paraffin,
and 150 cc of heptane was milled in a 500 cc capacity
tungsten carbide attritor mill using 2000 g of 3.2 mm
10 cemented tungsten carbide ball media for 2l~2 hr at 120 rpm.
For the compacts including other hard phase components,
the milling process was repeated, using a weight of hard
phase powder which would produce an equivalent volume
percent.
After milling, each batch of powder was separated ~rom
the milling media by washing with additional heptane
through a stainless steel screen. The excess heptane was
slowly evaporated. To prevent binder ~wax) inhomogeneity,
the thickened slurry was mixed continuously during
20 evaporation, and the caking powder broken up with a
plastic spatula into small, dry granules. The dry
granules were then sieved in two steps using 40- and
80-mesh screens. Each screened powder was then pressed at
138 MPa, producing green compacts measuring
16 ~ 16 x 6.6 mm and containing 50-60% by volume of solids
loading.
The pressed compacts were placed in a graphite boat,
covered with alumina sand, and placed in a hydrogen
furnace at room temperature. The temperature then was
30 raised in increments of 100 every hour and held at 300C
for 2 hr to complete the removal of the organic binder.
The dewaxed samples were then taken from the hot zone,
cooled to room temperature, and removed from the hydrogen
furnace.
The dewaxed samples were then densified in two steps:
presintering and hot isostatic pressing ~HIPing). The
~g-3-643 -17~
dewaxed compacts, on graphite plates which had been
sprinkled with coarse alumina sand, were presintered at
1650C for 1 hr at about 0.1 Torr in a cold wall graphite
vacuum furnace. The initial rise in temperature was
rapid, 15C/min up to 800C. From 800C the rise was
reduced to 4.5C/min. Throughout the entire presintering
cycle, the chamber pressure was maintained at about 0.1
Torr.
The final consolidation was carried out in a HIP unit
10 at 1650C and 207 MPa of argon for 1 hr, using a heating
rate of about 10C/min. The maximum temperature (1650C)
and pressure (207 MPa) were reached at the same time and
were maintained for about 1 hr, followed by oven cooling
to room temperature. The Knoop hardness at the surface of
each densified compact is shown in Table 4 below.
, ..~`..~`.J ~
89-3-643 -18-
TABLE 4
-
Powder Composition, v/oAve. Swrface
_ Hardness~,
S~mpla Ni+Al~ WCTiC TiB2 VC NbC TaC Knoop, MPa
~ _ _
11 10 90 - -- -- -- -- 17.D8
12 10 -- 90 -- -- -- -- 17.69
13 10 -- -- 90 -- -- -- 20~50
14 10 -- -- -- 90 -- -- 15.17
1 89 -- -- -- -- 15.43
- 16 10 7~.168.30 -- -- ~.183.36 14.77
CommPrcial 14.5
Tool ~lt
Co~mercial 13.4
Tool ~Zt
l.ON load.
~ 13.3% by weight Al, balan~e Ni.
20 t See Table 1 for co~positions.
As shown in Table 4, carbide compacts prepared as de-
scribed above axhibited improved hardness over that of
commercially available cutting tools. Titanium and
tungsten titanium carbide compacks prepared as described
above exhibited good performance in the dry turning of
1045 steel, 475 ft/min, 0.012 in/rev, 0.050 in D.O.C.
(depth of cut).
EXAMPLE 1Z
Compacts are prepared as described above for Examples
11-16, using the same powders in the starting formulations
and the same process, except that the dewaxed compacts are
presintered at 1500C for 1 hr. at 0.1 Torr in the same
~9-3-643 -19-
cold wall graphite vacuum furnace. The rise in
temperature is the same as in Example 1: initially rapid,
15~C/min. up to 800C. From 800C, the rise is reduced to
4.5C/min.
The metal bonded carbide cutting tool of Example 17 is
characterized by a specific microstructure in which a
gradient of hardness is developed from the surface of the
densified article to its core.
The present invention provides novel improved cutting
lO tools capable of withstanding the demands of hard steel
turning, which requires a high degree of wear resistance,
and steel milling, which requires a high degree of impact
resistance. It also provides wear parks and other
structural parts of high strength and wear resistance.
While there has been shown and described what are at
present considered the preferred embodiments of the
invention, it will be obvious to those skilled in the art
that various changes and modifications can be made therein
without departing from the scope of the invention as
20 defined by the appended Claims.
