U.S. patent application number 17/282062 was filed with the patent office on 2022-08-25 for hard metal having toughness-increasing microstructure.
The applicant listed for this patent is H.C. Starck Tungsten GmbH. Invention is credited to Juliane Meese-Marktscheffel, Carina Oelgardt, Johannes Potschke, Tino Sauberlich.
Application Number | 20220267882 17/282062 |
Document ID | / |
Family ID | 1000006390237 |
Filed Date | 2022-08-25 |
United States Patent
Application |
20220267882 |
Kind Code |
A1 |
Sauberlich; Tino ; et
al. |
August 25, 2022 |
Hard Metal Having Toughness-Increasing Microstructure
Abstract
The invention relates to a nanoscale or ultrafine hard metal,
comprising tungsten carbide, an additional metal carbide phase that
has a cubic crystal structure, and a binder metal phase. The
invention further relates to a method for producing said hard metal
and to the use of said hard metal to produce tools and wearing
parts. The invention further relates to a component that has been
produced from the described hard metal.
Inventors: |
Sauberlich; Tino; (Bad
Harzburg, DE) ; Meese-Marktscheffel; Juliane;
(Goslar, DE) ; Oelgardt; Carina; (Witten, DE)
; Potschke; Johannes; (Dresden, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
H.C. Starck Tungsten GmbH |
Munchen |
|
DE |
|
|
Family ID: |
1000006390237 |
Appl. No.: |
17/282062 |
Filed: |
September 20, 2019 |
PCT Filed: |
September 20, 2019 |
PCT NO: |
PCT/EP2019/075352 |
371 Date: |
September 22, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 29/08 20130101;
C22C 1/051 20130101; C22C 1/1084 20130101 |
International
Class: |
C22C 29/08 20060101
C22C029/08; C22C 1/05 20060101 C22C001/05; C22C 1/10 20060101
C22C001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2018 |
EP |
18200028.1 |
Claims
1. A cemented carbide, comprising a) a tungsten carbide phase
having an average grain size of from 0.05 to 0.5 .mu.m, preferably
from 0.05 to 0.23 .mu.m, more preferably from 0.05 to 0.09 .mu.m;
b) an additional metal carbide phase; and c) a binder metal phase,
wherein said additional metal carbide phase is in a cubic crystal
structure at room temperature, and wherein the proportion of said
additional metal carbide phase in said cemented carbide is at least
4% by volume, based on the total volume of the cemented carbide,
and wherein the average grain size was determined by the
linear-intercept technique according to ISO 4499-2.
2. The cemented carbide according to claim 1, characterized in that
said additional metal carbide phase is selected from the group
consisting of titanium carbide (TiC), tantalum carbide (TaC),
niobium carbide (NbC), hafnium carbide (HfC), zirconium carbide,
mixtures thereof, and mixed carbides of these compounds.
3. The cemented carbide according to claim 1 or 2, characterized in
that said additional metal carbide phase has an average grain size
of from 0.3 to 4 .mu.m, preferably from 0.5 to 1.5 .mu.m, as
determined by the linear-intercept technique according to ISO
4499-2.
4. The cemented carbide according to at least one of the preceding
claims, characterized in that said additional metal carbide phase
in the cemented carbide is in a periodically repeated distribution
with an average distance of from 0.5 to 10 .mu.m, preferably from 1
to 3 .mu.m, as determined by linear analysis (linear-intercept
technique) on electron micrographs of sections.
5. The cemented carbide according to at least one of the preceding
claims, characterized in that a tungsten carbide powder having an
average particle size d.sub.BET of from 0.05 to 0.3 .mu.m,
preferably from 0.05 to 0.25 .mu.m, more preferably from 0.05 to
0.2 .mu.m, is used as a starting material, as determined according
to the BET surface area by converting it according to the formula
d.sub.BET=6/(BET surface area*density).
6. The cemented carbide according to at least one of the preceding
claims, characterized in that a metal carbide powder having an
average particle size d.sub.BET of from 0.3 to 5 .mu.m, more
preferably from 0.4 to 1 .mu.m, is used as a starting material, as
determined according to the BET surface area, and by conversion
according to the formula d.sub.BET=6/(BET surface
area*density).
7. The cemented carbide according to at least one of the preceding
claims, characterized in that said binder metal phase is selected
from the group consisting of iron, cobalt, nickel, and mixtures
thereof.
8. The cemented carbide according to claim 7, characterized in that
said binder metal phase is a mixture consisting of iron, cobalt,
and nickel, in which the respective contents of the components are
more than 1% by mass.
9. The cemented carbide according to at least one of the preceding
claims, characterized in that said cemented carbide further
includes grain growth inhibitors, preferably those selected from
the group consisting of vanadium carbide, chromium carbide,
mixtures thereof, and mixed carbides of such compounds.
10. The cemented carbide according to at least one of the preceding
claims, characterized in that said tungsten carbide phase in the
cemented carbide comprises from 40 to 90% by volume, based on the
total volume of the cemented carbide.
11. The cemented carbide according to at least one of the preceding
claims, characterized in that said cemented carbide has a thermal
conductivity of less than 50 W/m*K, as determined by the laser
flash technique at 40.degree. C.
12. A process for the preparation of a cemented carbide according
to one or more of claims 1 to 11, comprising the steps of: i)
providing a powder mixture, including a) a tungsten carbide powder
having an average particle size d.sub.BET of from 0.05 to 0.3
.mu.m; b) an additional metal carbide powder that is in a cubic
crystal structure at room temperature (25.degree. C.) and has an
average particle size d.sub.BET of from 0.3 to 5 .mu.m; and c) a
binder metal powder; and ii) forming and sintering the mixture.
13. The process according to claim 12, characterized in that said
sintering is effected at a temperature of from 1150 to 1550.degree.
C.
14. Use of a cemented carbide according to one or more of claims 1
to 11 for the production of tools.
15. A component, characterized by being obtained by forming the
cemented carbide according to one or more of claims 1 to 11.
16. The component according to claim 15, characterized in that said
component is drills, solid carbide cutters, indexable inserts, saw
teeth, forming dies, sealing rings, extrusion punches, press dies,
and wear parts.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is the national stage entry of
International Patent Application No. PCT/EP2019/075352 having a
filing date of Sep. 20, 2019, which claims priority to and the
benefit of European Patent Application No. 18200028.1 filed in the
European Patent Office on Oct. 12, 2018, the entire contents of
which are incorporated herein by reference.
[0002] The present invention relates to a nanoscale or ultrafine
cemented carbide including tungsten carbide, an additional metal
carbide phase that is in a cubic crystal structure, and a binder
metal phase, to a process for the preparation thereof, and to the
use thereof for preparing tools and wear parts. Further, the
present invention relates to a component prepared from the cemented
carbide described.
[0003] Cemented carbides are metal matrix composite materials in
which hard materials in the form of small particles are cemented
together by a matrix of metal. Cemented carbides are employed
predominantly in applications in which materials having a high wear
resistance and hardness while showing a high strength are required.
Thus, cemented carbides are used, for example, as a cutting
material for tools (such as turning tools, drills, and milling
tools) and as wear-resistant matrices, e.g., in reforming or
punching tools. However, conventional cemented carbides have the
drawback of having a very low fracture toughness, which
significantly limits their applicability. Conventionally,
increasing the fracture toughness is possible by increasing the
content of binder metal, which results in a decrease of hardness,
however. Ideally, a tool made of a cemented carbide should have a
high hardness while also having a high fracture toughness.
[0004] U.S. Pat. No. 5,593,474 describes a sintered body of a
composite material comprising a plurality of regions of a first
metal carbide; and a plurality of regions of a second metal
carbide, the first metal carbide having a larger particle size than
the second metal carbide.
[0005] DE 10 2004 051 288 addressed the object or providing a
polycrystalline powder of hard material with improved hardness
while the toughness is maintained. This object is achieved by a
polycrystalline powder of hard material consisting of
polycrystalline grains of hard material, which are made of crystals
of carbides, nitrides and/or carbonitrides of the transition metals
of groups 4, 5 and 6 (titanium, vanadium and chromium groups) of
the Periodic Table.
[0006] WO 2017/186468 relates to a cemented carbide comprising a
phase of hard material grains and a phase of a heterogeneously
distributed binder metal, wherein said hard material grains have an
average grain size within a range of from 1 nm to 1000 nm, and said
heterogeneously distributed binder metal is present in the form of
binder islands within the cemented carbide that have an average
size 0.1 .mu.m to 10 .mu.m, and an average distance between
neighboring binder islands of from 1 .mu.m to 7 .mu.m.
[0007] EP 1 526 189 describes a cemented carbide comprising WC, a
binder phase based on Co, Ni or Fe, and a gamma phase in which said
gamma phase has an average particle size of less than 1 .mu.m. Said
gamma phase is prepared from presynthesized mixed carbides in the
form (Me,W)C.
[0008] CN 103540823 describes a cemented carbide composition
comprising from 40 to 50% by weight of WC, from 5 to 10% by weight
of vanadium carbide, from 3 to 8% by weight of chromium carbide,
from 5 to 9% by weight of titanium carbide, from 6 to 11% by weight
of tantalum carbide, from 2 to 5% by weight of niobium carbide, and
from 12 to 18% by weight of cobalt. The particle size of said WC is
within a range of from 0.1 to 0.8 .mu.m.
[0009] EP 1 557 230 relates to a cemented carbide body comprising
from 10 to 12% by weight of cobalt, less than 3% by weight of
tantalum carbide, from 1 to 5.5% by weight of niobium carbide, and
from 3 to 5% by weight of titanium carbide, the balance being WC.
Said WC has a particle size of from 0.4 to 1.5 .mu.m, especially
from 0.8 to 1.5 .mu.m.
[0010] U.S. Pat. No. 4,698,266 discloses a cutting tool comprising
a maximum of 70% by weight of WC, and from 5 to 10% by weight of a
cobalt binder phase, the rest of the composition being formed by
metal carbides selected from the group consisting of TiC, TaC, NbC,
HfC, and mixtures thereof. The average grain size of said WC is
from 0.9 to 1.3 .mu.m.
[0011] Even if some solution approaches are already offered in the
prior art, there is still no commercial solution for cemented
carbides that have both a high hardness and wear resistance, and a
high fracture toughness.
[0012] Therefore, it is the object of the present invention to
provide a cemented carbide that pas an improved combination of
hardness and fracture toughness, and preferably is accessible in a
simple way.
[0013] Surprisingly, it has been found that this object is achieved
by providing a nanoscale or ultrafine cemented carbide based on
tungsten carbide, which further includes a metal carbide phase that
is in a cubic crystal structure at room temperature.
[0014] Therefore, the present invention first relates to a cemented
carbide, comprising [0015] a) a tungsten carbide phase having an
average grain size of from 0.05 to 0.5 .mu.m; [0016] b) an
additional metal carbide phase; and [0017] c) a binder metal
phase,
[0018] wherein said additional metal carbide phase is in a cubic
crystal structure at room temperature, and wherein the proportion
of said additional metal carbide phase in said cemented carbide is
at least 4% by volume, based on the total volume of the cemented
carbide, and wherein the average grain size was determined by the
linear-intercept technique according to ISO 4499-2.
[0019] The conversion from percent by volume to percent by weight,
or the conversion from percent by weight to percent by volume, is
effected according to the following formulas:
m i = v i .rho. i 1 .SIGMA. .function. ( v i .rho. i ) .times. v i
= m i .rho. i 1 .SIGMA. .function. ( m i .rho. i ) ##EQU00001##
[0020] wherein m.sub.i represents the mass proportion, v.sub.i
represents the volume proportion, and .rho..sub.i represents the
density of the respective component.
[0021] The cemented carbide according to the invention is a
nanoscale or ultrafine cemented carbide, whose classification is
effected in accordance with ISO 4499-2.
[0022] Within the scope of the present invention, "cemented
carbide" describes a sintered composite material. Said additional
metal carbide phase, which is in a cubic crystal structure at room
temperature, i.e., at 25.degree. C. within the scope of the present
invention, is hereinafter referred to interchangeably as a "cubic
metal carbide".
[0023] The cemented carbide according to the invention has a high
hardness and a high fracture toughness. The problem that the
fracture toughness decreases as the hardness of the cemented
carbide increases, i.e., that the material becomes brittle and
friable, which occurs in conventional cemented carbides, was not
observed in the case of the cemented carbide according to the
invention. Without being bound by theory, it is considered that the
positive properties of the cemented carbide according to the
invention can be attributed, in particular, to the combination of
the small grain size of the tungsten carbide and the presence of
the cubic metal carbide phase. Therefore, the tungsten carbide used
in the cemented carbide according to the invention has an average
grain size of from 0.05 to 0.5 .mu.m, preferably from 0.05 to 0.23
.mu.m, more preferably from 0.05 to 0.09 .mu.m, as determined by
the linear-intercept technique according to ISO 4499-2.
[0024] In a further preferred embodiment, the metal carbide phase
that is in a cubic crystal structure at room temperature is
selected from the group consisting of titanium carbide, tantalum
carbide, niobium carbide, hafnium carbide, zirconium carbide,
mixtures thereof, and mixed carbides of these compounds.
[0025] Preferably, the metal carbide phase used in the cemented
carbide according to the invention has an average grain size of
from 0.3 to 4.0 .mu.m, preferably from 0.5 to 1.5 .mu.m, as
determined by the linear-intercept technique according to ISO
4499-2.
[0026] Surprisingly, it has been found that a particularly
advantageous relationship of hardness and fracture toughness could
be achieved if the metal carbide phases present in the cemented
carbide according to the invention are homogeneously distributed.
Therefore, an embodiment is preferred in which the metal carbide
phase contained in the cemented carbide is in a periodically
repeated distribution with an average distance of from 0.5 to 10
.mu.m, preferably from 1 to 3 .mu.m. Said average distance can be
determined by linear analysis (linear-intercept technique) on
electron micrographs of sections, and relates to the distance from
grain center to grain center. Without being bound by theory, the
particularly homogeneous distribution of the metal carbide phase in
the cemented carbide according to the invention is attributed,
inter alia, to the use of a tungsten carbide powder having the
above mentioned grain sizes.
[0027] It has been found advantageous if powders having a
particular particle size are used as starting materials for the
tungsten carbide and the cubic metal carbide, wherein a "starting
material" within the scope of the present invention means an
unsintered powder. Therefore, in a preferred embodiment, a tungsten
carbide powder having an average particle size d.sub.BET of from
0.05 to 0.30 .mu.m, preferably from 0.05 to 0.25 .mu.m, more
preferably from 0.05 to 0.2 .mu.m, is used as a starting material.
The average particle size d.sub.BET is calculated from the specific
surface area of the starting material as determined according to
BET (BET surface area) by converting it according to the formula
d.sub.BET=6/(BET surface area*density). The specific surface area
can be determined by the BET method according to DIN ISO 9277. The
density corresponds to the physical density of the pure solid and
can be extracted from the literature, the density of tungsten
carbide usually being stated as 15.7 g/cm.sup.3.
[0028] As the starting material for the cubic metal carbide, there
is preferably employed a cubic metal carbide powder having an
average particle size d.sub.BET of from 0.3 to 5 .mu.m, more
preferably from 0.4 to 1 .mu.m, as determined according to the BET
surface area of the starting material, and by conversion according
to the formula d.sub.BET=6/(BET surface area*density). The physical
density of the respective cubic carbide is to be used as said
density. The values can be extracted from the literature.
[0029] In a preferred embodiment, the binder metal is a compound
selected from the group consisting of cobalt, iron, nickel, and
mixtures thereof. More preferably, the binder metal is cobalt. In a
further preferred embodiment, the binder metal is a mixture
consisting of iron, cobalt, and nickel, in which the proportion of
the respective metals in the mixture is more than 1% by mass.
[0030] Surprisingly, it has been found that the sole addition of
the cubic metal carbides as described above has no influence on
grain growth during the production process, so that grain growth
inhibitors may be optionally added to the cemented carbide
according to the invention for reducing grain growth during the
production process thereof. Therefore, an embodiment is preferred
in which the cemented carbide further includes grain growth
inhibitors, preferably those selected from the group consisting of
vanadium carbide, chromium carbide, mixtures thereof, and mixed
carbides of such compounds. The proportion of grain growth
inhibitor in the cemented carbide is preferably from 0.05 to 6% by
volume, based on the total volume of the cemented carbide.
[0031] Within the scope of the present invention, it has been found
advantageous if the proportion of tungsten carbide in the cemented
carbide according to the invention does not exceed a proportion of
95% by volume. Therefore, an embodiment is preferred in which the
proportion of tungsten carbide in the cemented carbide according to
the invention is from 40 to 80% by volume, based on the total
volume of the cemented carbide. In this way, a sufficient hardness
and fracture toughness of the cemented carbide can be ensured.
[0032] Further, it has been found advantageous to limit the
proportion of binder metal in the cemented carbide. Therefore, an
embodiment is preferred in which the proportion of binder metal in
the cemented carbide according to the invention is not more than
40% by volume, preferably from 10 to 32% by volume, respectively
based on the total volume of the cemented carbide.
[0033] Surprisingly, it has been found that the hardness of the
cemented carbide can be increased while the fracture toughness is
maintained, if the volume proportion of the additional metal
carbide phase in the cemented carbide according to the invention
comprises at least 4% by weight. Therefore, an embodiment is
preferred in which the proportion of the additional metal carbide
phase is from 4 to 30% by volume, preferably from 10 to 20% by
volume, alternatively from 25 to 37% by volume, respectively based
on the total volume of the cemented carbide.
[0034] In a particularly preferred embodiment, the cemented carbide
according to the invention has the following composition: [0035] i)
from 40 to 90% by volume of tungsten carbide phase; and [0036] ii)
from 10 to 32% by volume of binder metal phase; and
[0037] balance: additional metal carbide phase;
[0038] wherein the proportion of the additional metal carbide phase
is at least 4% by volume, based on the total volume of the cemented
carbide, and wherein said percent by volume are respectively based
on the total volume of the cemented carbide and sum up to 100% by
volume, optionally considering further components, such as grain
growth inhibitors.
[0039] Conventional cemented carbides have the disadvantage that
although the hardness is increased by reducing the content of
binder metal, the fracture toughness decreases. At the same time,
an undesirable increase of thermal conductivity may occur.
Surprisingly, it has been found that the cemented carbide according
to the invention has an advantageous thermal conductivity. In a
preferred embodiment, the cemented carbide according to the
invention has a thermal conductivity of less than 50 W/m*K,
preferably less than 40 W/m*K, as determined by the laser flash
technique at 40.degree. C.
[0040] In addition to an advantageous thermal conductivity, the
cemented carbide according to the invention is further
characterized by an improved fracture toughness. Therefore, an
embodiment is preferred in which the cemented carbide according to
the invention has a fracture toughness of more than 8.0
MPa*m.sup.1/2, as determined from Vickers hardness impressions
according to the Palmquist method as described in Shetty et al.,
Journal of Materials Science 20 (1985), pp. 1873 to 1882.
[0041] The present invention further relates to a process for the
preparation of a cemented carbide according to the invention,
comprising: [0042] i) providing a powder mixture, including [0043]
a) a tungsten carbide powder having an average particle size
d.sub.BET of from 0.05 to 0.3 .mu.m, preferably from 0.05 to 0.25
.mu.m, more preferably from 0.05 to 0.2 .mu.m; [0044] b) an
additional metal carbide powder that is in a cubic crystal
structure at room temperature (25.degree. C.) and has an average
particle size d.sub.BET of from 0.3 to 5 .mu.m; and [0045] c) a
binder metal powder; and [0046] ii) forming and sintering the
mixture.
[0047] The average particle size d.sub.BET is determined as
described above from the BET surface area and conversion according
to the formula d.sub.BET=6/(BET surface area*density).
[0048] The proportion of said additional cubic metal carbide powder
in the powder mixture is selected for the cemented carbide obtained
to have a proportion of at least 4% by volume of the cubic metal
carbide phase, based on the total volume of the cemented
carbide.
[0049] The binder metal powders as stated above are preferably
used.
[0050] In a preferred embodiment, said forming and sintering of the
mixture is performed to obtain a cemented carbide body. Said
cemented carbide body may be, for example, a component.
[0051] In a preferred embodiment, the sintering within the scope of
the process according to the invention is effected at a temperature
of from 1150 to 1550.degree. C. In this way, the cemented carbide
according to the invention is accessible by a process that can be
realized simply in industry.
[0052] Within the scope of the present invention, it has been
surprisingly found that, for preparing the cemented carbide
according to the invention, it is not necessary to use
presynthesized mixed carbides of the form (Me,W)C, as described in
the prior art.
[0053] Rather, the cemented carbide according to the invention can
be prepared from the pure metal carbides or mixtures thereof.
[0054] The cemented carbide according to the invention is suitable,
in particular, for use in fields of application in which a high
hardness and at the same time a good fracture toughness are
required. Therefore, the present invention further relates to the
use of the cemented carbide according to the invention for the
production of tools. Preferably, the tools are tools with defined
and undefined cutting edges, and tools for the machining of all
kinds of materials.
[0055] The present invention further relates to a component
obtained by forming the cemented carbide according to the
invention. Preferably, the component is selected from the group
consisting of drills, solid carbide cutters, indexable inserts, saw
teeth, forming dies, sealing rings, extrusion punches, press dies,
and wear parts.
[0056] The present invention is further explained by means of the
following Examples, which are by no means to be understood as
limiting the idea of the invention.
EXAMPLES
Example 1
[0057] As the starting powder, a WC powder having a d.sub.BET value
of 90 nm, a cobalt metal powder having a d.sub.BET value of 205 nm,
a TiC powder having a d.sub.BET value of 610 nm, a TaC powder
having a d.sub.BET value of 370 nm, a Cr.sub.3C.sub.2 powder having
a d.sub.BET value of 430 nm, and a VC powder having a d.sub.BET
value of 350 nm were used. A 200 g mixture of 62.7% by volume (77%
by weight) WC, 15.9% by volume (11% by weight) Co, 12.9% by volume
(5% by weight) TiC, 4.4% by volume (5% by weight) TaC, 1.9% by
volume (1% by weight) Cr.sub.3C.sub.2, and 2.2% by volume (1% by
weight) VC was ground in n-heptane in a ball mill for 48 hours. The
dispersion of cemented carbide obtained was dried and pressed
uniaxially with a pressing power of 300 MPa into rectangular test
specimens with a green density of >50% of the density to be
expected for a solid body (theoretical density). The test specimens
were compacted under vacuum at a temperature of 1450.degree. C. and
with a holding time of 30 min to above 95% of the theoretical
density, followed by a final compaction under an argon atmosphere
at the same temperature (Sinter-HIP technology). The test specimens
proved to be completely dense under an optical microscope. The
porosity according to ISO 4505 corresponded to >A02, B00, C00.
The Vickers hardness was determined to be 1770 HV10, and the
fracture toughness (K.sub.1C) was calculated by measuring the crack
lengths and using the formula of Shetty (Shetty 1985--Indentation
fracture of WC-Co cermets, see reference above) to be 9.5
MPa*mJ.sup.1/2. The thermal conductivity (TC) was determined to be
29 W/m*K (measurement at 40.degree. C. by the laser flash
technique).
[0058] Table 1 shows the characteristics determined as compared to
a cemented carbide having a composition without additions of cubic
metal carbide, but with an otherwise comparable content of binder
metal.
Example 2
[0059] As the starting powder, a WC powder having a d.sub.BET value
of 90 nm, a cobalt metal powder having a d.sub.BET value of 205 nm,
a TiC powder having a d.sub.BET value of 610 nm, a TaC powder
having a d.sub.BET value of 370 nm, a Cr.sub.3C.sub.2 powder having
a d.sub.BET value of 430 nm, and a VC powder having a d.sub.BET
value of 350 nm were used. A 200 g mixture of 68.9% by volume
(80.6% by weight) WC, 16% by volume (10.6% by weight) Co, 4% by
volume (2.6% by weight) TiC, 7% by volume (4.3% by weight) TaC,
1.9% by volume (0.9% by weight) Cr.sub.3C.sub.2, and 2.2% by volume
(1% by weight) VC was ground in n-heptane in a ball mill for 48
hours. The dispersion of cemented carbide obtained was dried and
pressed uniaxially with a pressing power of 300 MPa into
rectangular test specimens with a green density of >50% of the
density to be expected for a solid body (theoretical density). The
test specimens were compacted under vacuum at a temperature of
1450.degree. C. and with a holding time of 30 min to above 95% of
the theoretical density, followed by a final compaction under an
argon atmosphere at the same temperature (Sinter-HIP technology).
The test specimens proved to be completely dense under an optical
microscope. The porosity according to ISO 4505 corresponded to
>A02, B00, C00. The Vickers hardness was determined to be 1690
HV10, and the fracture toughness (K.sub.1C) was calculated by
measuring the crack lengths and using the formula of Shetty (Shetty
1985--Indentation fracture of WC-Co cermets, see reference above)
to be 9.7 MPa*mJ.sup.1/2. The thermal conductivity (TC) was
determined to be 39 W/m*K (measurement at 40.degree. C. by the
laser flash technique).
[0060] Table 1 shows the characteristics determined as compared to
the characteristics from Example 1.
TABLE-US-00001 TABLE 1 Composition and achieved hardness, fracture
toughness, and thermal conductivity of nanoscale or ultrafine
cemented carbides having a content of binder metal of 16 .+-. 0.2%
by volume with and without additions of cubic metal carbide (MeC)
of 17 and 11% by volume, respectively. Comp. Ex. without MeC WC Co
TiC TaC Cr.sub.3C.sub.2 VC hardness 1783 .+-. 20 HV10 % by weight
89.1 10 0 0 0.6 0.3 K.sub.1C 8.9 MPa*m.sup.1/2 % by volume 81.7
16.2 0 0 1.3 0.8 TC 50 W/m*K Ex. 1 17% by volume MeC WC Co TiC TaC
Cr.sub.3C.sub.2 VC hardness 1770 .+-. 20 HV10 % by weight 77 11 5 5
1 1 K.sub.1C 9.5 MPa*m.sup.1/2 % by volume 62.7 15.9 12.9 4.4 1.9
2.2 TC 29 W/m*K Ex. 2 11% by volume MeC WC Co TiC TaC
Cr.sub.3C.sub.2 VC hardness 1690 .+-. 20 HV10 % by weight 80.6 10.6
2.6 4.3 0.9 1 K.sub.1C 9.7 MPa*m.sup.1/2 % by volume 68.9 16 4 7
1.9 2.2 TC 39 W/m*K
Example 3
[0061] As the starting powder, a WC powder having a d.sub.BET value
of 90 nm, a cobalt metal powder having a d.sub.BET value of 205 nm,
a TiC powder having a d.sub.BET value of 610 nm, a TaC powder
having a d.sub.BET value of 370 nm, a Cr.sub.3C.sub.2 powder having
a d.sub.BET value of 430 nm, and a VC powder having a d.sub.BET
value of 350 nm were used. A 200 g mixture of 68.5% by volume
(79.1% by weight) WC, 10% by volume (6.5% by weight) Co, 10.1% by
volume (3.7% by weight) TiC, 9% by volume (9.6% by weight) TaC,
1.2% by volume (0.6% by weight) Cr.sub.3C.sub.2 and 1.2% by volume
(0.5% by weight) VC was ground in n-heptane in a ball mill for 44
hours. The dispersion of cemented carbide obtained was dried and
pressed uniaxially with a pressing power of 300 MPa into
rectangular test specimens with a green density of >50% of the
density to be expected for a solid body (theoretical density). The
test specimens were compacted under vacuum at a temperature of
1460.degree. C. and with a holding time of 30 min to above 95% of
the theoretical density, followed by a final compaction under an
argon atmosphere at the same temperature (Sinter-HIP technology).
The test specimens proved to be completely dense under an optical
microscope. The porosity according to ISO 4505 corresponded to
>A02, B00, C00. The Vickers hardness was determined to be 2020
HV10, and the fracture toughness (K.sub.1C) was calculated by
measuring the crack lengths and using the formula of Shetty (Shetty
1985--Indentation fracture of WC-Co cermets, see reference above)
to be 8.5 MPa*m.sup.1/2. The thermal conductivity was determined to
be 35 W/m*K (measurement at 40.degree. C. by the laser flash
technique).
[0062] Table 2 shows the characteristics determined as compared to
a cemented carbide having a composition without additions of cubic
metal carbide, but with an otherwise comparable content of binder
metal.
TABLE-US-00002 TABLE 2 Composition and achieved hardness, fracture
toughness, and thermal conductivity of nanoscale or ultrafine
cemented carbides having a content of binder metal of 10 .+-. 0.2%
by volume with and without additions of cubic metal carbide (MeC).
Comp. Ex. without MeC WC Co TiC TaC Cr.sub.3C.sub.2 VC hardness
2010 .+-. 20 HV10 % by weight 93.1 6 0 0 0.6 0.3 K.sub.1C 8.0
MPa*m.sup.1/2 % by volume 87.9 10 0 0 1.3 0.8 TC 61 W/m*K Ex. 3 19%
by volume MeC WC Co TiC TaC Cr.sub.3C.sub.2 VC hardness 2020 .+-.
20 HV10 % by weight 79.1 6.5 3.7 9.6 0.6 0.5 K.sub.1C 8.5
MPa*m.sup.1/2 % by volume 68.5 10.0 10.1 9.0 1.2 1.2 TC 35
W/m*K
[0063] As can be seen from Tables 1 and 2, the cemented carbides of
the invention according to the Examples have a fracture toughness
that is improved over that of conventional cemented carbides, and a
lower thermal conductivity without adversely affecting the Vickers
hardness of the cemented carbides according to the invention within
the accepted tolerance of .+-.20 HV10.
[0064] FIG. 1 shows a scanning electron micrograph of a cemented
carbide according to the invention, which shows the periodically
repeated distribution of the additional metal carbide phase with an
average distance of about 1 to 3 .mu.m. The picture was recorded on
an electron microscope with an EsB detector having an acceleration
voltage of 2 kV and a 10,000.times. magnification. The numbers
represent:
[0065] 1--tungsten carbide phase
[0066] 2--cubic metal carbide phase
[0067] 3--binder metal phase
* * * * *