Method of making cemented carbide articles and the resulting articles

The present invention relates to a method of producing a sintered body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgical methods milling, pressing and sintering of powders. At least part of the binderphase powder consists of non-agglomerated particles of spheroidal morphology having dimensions of 0.1 to 20 .mu.m.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of making cemented carbide 
articles using binder phase powders with spherical, non-agglomerated 
particles. 
Cemented carbide contains mainly tungsten carbide and cobalt, often along 
with certain other carbides, e.g., carbides of titanium, tantalum, 
niobium, chromium, etc. It contains at least one hard but brittle 
(carbide) phase and a relatively less hard but ductile and tough metal 
(binder) phase, particularly cobalt. This results in materials combining 
hardness and toughness which have found many applications, for instance in 
rock drilling and metal cutting tools, wear parts, etc. 
Cemented carbide is made by techniques usual in powder metallurgy, that is: 
mixing the constituent powders (carbides, cobalt and possibly other hard 
materials) by milling, using mills (rotating ball mills, vibrating mills, 
attritor mills, etc.) equipped with non-polluting milling media which 
themselves are made of cemented carbide. The milling is made in the 
presence of an organic liquid (for instance ethyl alcohol, acetone, etc.) 
and an organic binder (for instance paraffin, polyethylene glycol, etc.) 
in order to facilitate the subsequent granulation operation; 
granulation of the milled mixture according to known techniques, in 
particular spray drying. The suspension containing the powdered materials 
mixed with the organic liquid and the organic binder is atomized through 
an appropriate nozzle in the drying tower where the small drops are 
instantaneously dried by a stream of hot gas, for instance, a stream of 
nitrogen. The granules collected at the lower end of the tower have an 
average diameter adjustable by the choice of appropriate nozzles, between 
100 and 200 .mu.m. Such granules flow easily, in contrast to fine or 
ultra-fine powders. The formation of granules is necessary in particular 
for the automatic feeding of compacting tools used in the subsequent 
stage; 
compaction of the granulated powder in a matrix with punches (uniaxial 
compaction) or in a bag (isostatic compaction), in order to give the 
material the shape and dimensions as close as possible (considering 
shrinkage) to the dimension wished for the final body. If necessary, the 
compacted body can be subjected to a machining operation before sintering; 
and 
sintering of the compacted bodies at a temperature and for a time 
sufficient to obtain dense bodies with a suitable structural homogeneity. 
The sintering can equally be carried out at high gas pressure (hot 
isostatic pressing), or the sintering can be complemented by a sintering 
treatment under moderate gas pressure (process generally known as 
SINTER-HIP). 
The sintered cemented carbides can be characterized in particular by their 
porosity and their microstructure (observed by optical or electron 
microscopy). 
The cobalt powders conventionally used in the cemented carbide industry are 
obtained by calcining cobalt hydroxide or oxalate followed by a reduction 
of the oxide so obtained by hydrogen; see for instance, "Cobalt, its 
Chemistry, Metallurgy and Uses", R. S. Young Ed., Reinhold Publishing 
Corporation (1960) pages 58-59. These conventional cobalt powders are 
characterized by a broad particle size distribution with strongly 
aggregated particles in the form of agglomerates with a sponge-like 
aspect, which are difficult to mill since there are strong binding forces 
between the elementary particles in these aggregates. 
In U.S. Pat. No. 4,539,041, the disclosure of which is herein incorporated 
by reference, the making of metallic powders by a process for reducing 
oxides, hydroxides or metal salts with the aid of polyols, is described. 
Particularly when starting with cobalt hydroxide, it is possible to obtain 
powders of metallic cobalt as essentially spherical, non-agglomerated 
particles. Further studies have shown in particular that it is possible to 
obtain non-agglomerated metallic powders having controlled average 
diameters of the particles, for instance by varying the .concentration of 
the starting hydroxide or metal salt, in relation to the polyol(s). Thus, 
in the case of cobalt, it is possible to obtain particles with an average 
diameter of, for instance 1, 2 or 3 .mu.m, by using the ratios cobalt 
hydroxide/polyol of 0.033, 0.1 or 0.340 g cobalt/cm.sup.3 polyol, 
respectively. Similarly, it is possible to obtain particles with 
adjustable average dimensions, smaller than 1 .mu.m by seeding the 
reaction mixture with the aid of very fine metallic particles (for 
instance palladium) either by adding a metal salt or hydroxide reacting 
more quickly than the cobalt salt or hydroxide with the polyol. This is 
particularly the case with silver salts, in particular silver nitrate, 
which are quickly reduced to metallic silver in the form of very fine 
particles of which the number is roughly proportional to the quantity of 
silver introduced into the reaction chamber. The silver or palladium 
particles so formed serve as seeds for the growth of cobalt particles 
which are subsequently formed by reduction of the cobalt hydroxide or salt 
by the polyol. The higher the number of seed particles, the smaller the 
dimensions of the final cobalt particles. For instance, when using a molar 
ratio silver/cobalt in the range of 10.sup.-4 -10.sup.-2, one can obtain 
cobalt particles having average dimensions that vary from 0.1 to 0.3 .mu.m 
and the range can be extended by varying this ratio between 10.sup.-5 and 
10.sup.-1 for all the appropriate metals. These various methods for 
controlling the size of the metallic particles are particularly known and 
described by M. Figlarz et al, M.R.S. International Meeting on Advanced 
Materials, Vol. 3, Materials Research Society, pp. 125-140 (1989); F. 
Fievet et al, Solid State Ionics 32/33, 198-205 (1989); and F. Fievet et 
al, M.R.S Bulletin, December 1989, pp. 29-34. 
OBJECTS, SUMMARY AND ADVANTAGES OF THE INVENTION 
It is an object of this invention to avoid or alleviate the problems of the 
prior art. 
It is also an object of this invention to provide an improved process for 
making cemented carbide bodies by powder metallurgical techniques, the 
resulting bodies and methods for their use. 
In one aspect of the invention there is provided a method of making a 
sintered body comprising: 
mixing powders comprising a hard constituent and a metallic binder of 
cobalt, nickel and/or iron, said metallic binder comprising 
non-agglomerated spherical particles having dimensions in the range of 
from 0.1 to 20 .mu.m; 
pressing the mixed powders into a compact; and 
sintering the pressed compact. 
In another aspect of the invention there is provided a sintered cemented 
carbide body comprising WC and a binder phase comprising cobalt and/or 
nickel, said body having a porosity better than A02 and B00, less than 0.5 
binder phase lakes per cm.sup.2 with a maximum dimension of &gt;25 .mu.m and 
less-than five carbide grains per cm.sup.2 with a grain size of more than 
5 times the average grain size of the matrix. 
It has now been discovered that cobalt powders having the properties of 
those obtained by the reduction of cobalt hydroxide or a cobalt salt with 
the aid of polyol, according to U.S. Pat. No. 4,539,041 and the references 
just mentioned, that is, powders of individual, essentially spherical 
non-agglomerated particles, can be used as binder phase powder in the 
manufacture of cemented carbide and that this preparation gives several 
advantages which are discussed below. 
It has been particularly discovered that when using such non-agglomerated 
cobalt powders, it is possible to obtain in a reproducible way, cemented 
carbide exhibiting interesting characteristics, in particular, reduced 
porosity. It is also possible to decrease the milling time for starting 
mixtures (carbide and binder) without impairing the quality of the final 
cemented carbide. Acceptable results can be obtained even after a simple 
blending operation. Alternatively, the degree of milling may be further 
reduced and the cemented carbide subjected to a hot isostatic pressing 
process, either incorporated into the sintering process or as a separate 
operation, giving an increase in the grain size of the hard phase and 
correspondingly an increase in resistance to thermal cracking. 
In addition, it has been discovered that, due to the use of such cobalt 
powders, it is possible to sinter at temperatures below those which are 
generally used. This decrease of sintering temperature: is interesting not 
only from an energy point of view, but also because it possibly permits 
the possibility of adding to the powder mixture other hard or superhard 
materials (in the form of powders) which cannot normally be used at the 
temperature required for conventional sintering. Among these other 
superhard materials, one can note particularly diamond, of which it is 
known that it starts transforming into graphite in air at a temperature 
around 800.degree. C. and cubic boron nitride. Alternatively, the 
sintering temperature may be lowered even further and the cemented carbide 
subjected to a hot isostatic pressing process, either incorporated into 
the sintering process or as a separate operation, giving an increased 
hardness level and a more uniform grain size and binder phase distribution 
leading to an increase in mechanical strength. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
Generally, the cobalt particles used as binder phase according to the 
invention have dimensions that can vary from 0.1 to 20 .mu.m, preferably 
from 0.1 to 10 .mu.m, most preferably from 0.1 to 5 .mu.m. Especially 
interesting results have been obtained with submicron particles (that is 
with a size less than 1 .mu.m). 
The present invention has thus as an object the use, as at least part of 
the binder phase, in the preparation of cemented carbide by milling and 
sintering a mixture of powders with at least one hard material based on 
tungsten carbide and a binder phase, of at least one powder of cobalt, 
that is homogeneous as regards the size of the particles, and particularly 
one powder having an average particle size x (in the range discussed 
above), of which at least 80% of the particles have sizes in the range 
x.+-.0.2x, provided the range of variation (that is, 0.4x) is not smaller 
than 0.1 .mu.m. The cobalt powder used in accordance with the invention 
consists of individual, essentially spherical, non-agglomerated particles. 
Such powders can be especially obtained with the polyol reduction which is 
discussed again below. It is preferable to start with cobalt hydroxide or 
cobalt acetate. 
The cobalt powders obtained by the reduction of cobalt hydroxide with the 
aid of polyol generally contain a small proportion of carbon (most often 
less than 1.5% by weight) and oxygen (most often less than 2.5% by 
weight). These powders can be directly used in the manufacture of cemented 
carbides. 
Generally, according to the present invention the cobalt powder used as the 
binder in the preparation of cemented carbide will exclusively be a powder 
as defined above. But it is possible to use such powders in combination 
with a second cobalt powder exhibiting other characteristics, provided the 
proportion of the first powder is sufficient for giving the advantages 
indicated in the preparation of cemented carbide, for instance, a decrease 
of the sintering temperature. Generally, the first powder represents at 
least 10%, and preferably at least 50% of the total weight of the cobalt 
used as binder phase. 
In addition, it is possible to use as binder phase a mixture of two or more 
powders as defined above, these two powders having different average 
particle dimensions. 
It has also been found that the use of cobalt according to the invention is 
very suitable to adjust the binder content of an already dried cemented 
carbide mixture. Such an adjustment is not possible with a conventional 
binder phase powder since the resulting mixture lacks necessary 
flowability. Adding polyol reduced cobalt does not adversely affect 
flowability and can even improve it. Thus, a unique `mother-mix` may be 
used for producing a variety of cemented carbide grades having different 
binder phase contents. After the addition of the polyol reduced cobalt, 
preferably with a particle size of &lt;3 .mu.m, up to the desired content, 
the mixture is homogenized (e.g., blended) before pressing and sintering. 
The starting powder mixture contains cobalt in sufficient proportions for 
the final cemented carbide to contain 0.1 to 40% by weight of cobalt, and 
preferably 3 to 25%. It is particularly advantageous in grades with very 
low contents of cobalt (typically &lt;0.5%) often referred to as binderless 
grades. 
Sintered cemented carbide bodies based on WC, particularly with a grain 
size &lt;1.5 .mu.m, manufactured according to the method of the invention has 
a porosity better than A02 and B00, less than 0.5, preferably less than 
0.2, binder phase lakes per cm.sup.2 with a maximum dimension of &gt;25 .mu.m 
and less than five carbide grains per cm.sup.2 with a grain size of more 
than 5 times the average grain size of the matrix. 
In the manufacture of cemented carbides where the sintered grain size of 
the hard phases is fine, i.e., 1 .mu.m or less, it is commonplace to 
substitute a small amount of other refractory metal carbides for tungsten 
carbide. The carbides commonly used are those of titanium, tantalum, 
niobium, vanadium, chromium and hafnium. The effect of these substitutions 
is to control grain growth of the hard phase during sintering. A side 
effect is that they inhibit melt formation during sintering with the 
result that often higher sintering temperatures are needed than would be 
the case without the substitution to ensure freedom from microporosity and 
a uniform binder phase (cobalt-rich phase) distribution. The result is to 
partly negate the advantage of the substitution, leading to a degree of 
grain growth, recrystallization, of the WC-phase which results in a 
non-uniform hardness level less than the optimum hardness level and a 
reduction in mechanical strength. Using the cobalt polyol reduced-powder 
according to the present invention, the above-mentioned grain growth 
inhibitors may be excluded. This applies in particular to high pressure 
anvils for diamond production in which the cobalt-content of the cemented 
carbide is 5-7 weight-% and WC grain size &lt;1.5 .mu.m. Another example is 
tools such as drills, microdrills and routers for machining of printed 
circuit boards and similar composite materials. Such tools have a cobalt 
content of 3-20 weight-%, preferably 4-12 weight-% and a WC grain size of 
&lt;1 .mu.m, preferably &lt;0.7 .mu.m. 
For certain applications where a degree of thermal shock is experienced, 
for example, hot rolling of steel bar, some mining and highway engineering 
applications and machining of stainless steel, it is desired that the hard 
phases should be of relatively coarse grain size, typically greater than 4 
.mu.m, preferably greater than 6 .mu.m, and the cobalt content &lt;10 
weight-%, preferably &lt;8 weight-%. A cemented carbide powder to produce 
such a sintered hard phase grain size must of necessity be 
relatively-lightly milled in order to control the degree of comminution. 
The result is that the degree of intimate mixing is reduced, and, owing to 
the coarse particle size, the area available for reaction during sintering 
to produce a melt is relatively small. Consequently, such cemented carbide 
powders prove to be difficult to sinter and require high temperatures to 
approach a fully dense condition. Using the non-agglomerated, spherical 
cobalt powder of the present invention, dense bodies can be obtained at a 
lower sintering temperature. 
In U.S. Pat. No. 4,743,515, the disclosure of which is hereby incorporated 
by reference, it has been shown that an increased strength was obtained in 
sintered bodies of cemented carbide used in tools for rock drilling. The 
buttons according to this patent have a core consisting of a fine-grained 
eta-phase M.sub.6 C (e.g., Co.sub.3 W.sub.3 C) and/or M.sub.12 C (e.g., 
Co.sub.6 W.sub.6 C), embedded in normal alpha (WC) and beta (Co binder) 
phase structure at the same time as the sintered body has a surrounding 
surface zone which consists of alpha- and beta-phase in two areas whereas 
the outer shell is cobalt depleted and the inner part has a high content 
of binder phase. Surprisingly, it has now been found that cemented carbide 
bodies manufactured in such a way as described above give a more optimized 
toughness behavior when cobalt according to the present invention is used 
in the production of the buttons. The effect is most pronounced for 
cemented carbide with a cobalt content of more than 10% and less than 25% 
by weight and preferably 13-20% by weight of cobalt. The mean grain size 
of the hard constituents is more than 1.5 .mu.m. The same appearance has 
also been obtained for cemented carbide bodies with mean grain size of 
alpha-phase (WC) of less than 1.2 .mu.m and a binder content of equal or 
less than 6% by weight of cobalt. When cobalt according to the invention 
is used in the sintering/heat treatment procedure, the sintering 
temperature can be reduced which results in a lower carbon content in the 
binder phase and a low porosity level. The benefit of this sintering/heat 
treatment gives a product with a high carbon activity and a fine grain 
size eta-phase which results in a cemented carbide body with a more 
pronounced difference in cobalt content in the surface zone between the 
outer cobalt depleted shell and the inner part rich with cobalt. The 
cemented carbide produced with the cobalt according to the present 
invention has a cobalt content with greater difference and reduced width 
of the shells in the surface zone which leads to higher compressive 
stresses in the surface zone and has also positive effects on strength and 
toughness. 
The invention has been described above with reference to the manufacture of 
conventional cemented carbide, i.e., based upon WC and with a binder phase 
of cobalt. It is evident that the invention also can be applied to the 
manufacture of articles of other composite materials with hard 
constituents (borides, carbides, nitrides, carbonitrides, etc.) and a 
binder phase, based on cobalt, nickel and/or iron, such as titanium based 
carbonbitride alloys usually named cermets. Said alloys are manufactured 
by milling powders of carbides, nitrides and/or carbonitrides of mainly Ti 
but also of other metals from groups IVa, Va and VIa of the Periodic Table 
(V, Zr, Nb, Mo, Ta, W etc.) together with powders of nickel and cobalt. 
The mixture is then dried, pressed and sintered as de, scribed above for 
conventional cemented carbide.

The invention is additionally illustrated in connection with the following 
Examples which are to be considered as illustrative of the present 
invention. It should be understood, however, that the invention is not 
limited to the specific details of the Examples. 
EXAMPLE 1 
A suspension of cobalt hydroxide was added to a mixture of monoethylene 
glycol and diethylene glycol, while agitating. The suspension, containing 
about 200 g of cobalt hydroxide per liter, was progressively heated to a 
temperature of at least 200.degree. C., while being strongly agitated. A 
solution of silver nitrate was then added to the monoethylene glycol, so 
that between 0.07 and 0.3 g silver per liter was introduced. The mixture 
was kept at the same temperature for 2 hours, and was then left to cool to 
room temperature. 
In this way a cobalt powder (reference p1 ) was obtained with the following 
properties: 
SEM diameter of the particles: 0.4 .mu.m 
C: 1.36% by weight 
O: 2.23% by weight 
The SEM diameter is the average diameter of the particles measured in the 
scanning electron microscope. 
In addition, the following raw materials were used: 
Tungsten carbide: 
Origin: Eurotungstene Poudres (France) 
Total carbon: 6.15% by weight 
Free carbon: 0.05% by weight 
Average diameter (Fisher): 0.9 .mu.m 
Tantalum carbide: 
Origin: H. C. STARCK 
Total carbon: 6.81% by weight 
Free carbon: 0.10% by weight 
Niobium: 9.09% by weight 
Cobalt (reference F) obtained by reduction of the oxide with hydrogen 
according to the conventional process: 
Origin: Eurotungstene Poudres 
Diameter according to Fisher: 1.30 .mu.m 
C: 0.012% by weight 
With the aid of these materials the following mixtures were prepared: 
Cobalt: 3% or 6.5% by weight 
Tantalum carbide: 0.5% by weight 
Tungsten carbide balance 
The powder mixture (500 g) in each case was obtained by milling in a mill 
of the "Attritor" type with a capacity of 9 liters, containing 3.5 kg of 
milling media (balls of cemented carbide with a diameter of 3 mm) turning 
at 250 turns per minute, in the presence of 200 ml of ethyl alcohol (or 
acetone) and with the addition of polyethylene glycol (2 g per 100 g of 
mixture). The powder was milled during 7 or 14 hours and thereafter 
granulated using a sieve with 120 .mu.m mesh size. The compaction was 
carried out under uniaxial compaction from two directions, with matrix and 
punches of cemented carbide under a pressure of 125 MPa. Sintering was 
performed at 1375.degree., 1410.degree. and 1450.degree. C. respectively. 
After sintering, microsections were prepared and the porosity and 
recrystallization were determined. 
The porosity was determined according to the standard ISO 4505 and is 
expressed with the aid of a scale of increasing porosity from A00 to A08. 
The recrystallization of tungsten carbide (or general grain growth) was 
determined by microscopic examination and visual comparison with an 
internal standard scale (analogous to that of the ISO scale for the 
:porosity) since no standard exists to this day. The results are expressed 
with a scale going from R1 (quasi-absence of recrystallization) to R5 
(very strong recrystallization). 
a) Cobalt: 6.5% by weight 
Milling: 14 hours 
Sintering: 1450.degree. C. 
Results: 
______________________________________ 
Type of cobalt 
P1 (Invention) 
F (Conventional) 
______________________________________ 
Porosity A02 A03/04 
Recrystallization 
R2/R3 R4/R5 
______________________________________ 
b) Cobalt: 6.5% by weight 
Milling: 7 hours 
Sintering: 1450.degree. C. 
______________________________________ 
Type of cobalt 
P1 (Invention) 
F (Conventional) 
______________________________________ 
Porosity A02 A04 
Recrystallization 
R2 R2/R3 
______________________________________ 
c) Cobalt: 3% by weight 
Milling: 14 hours 
Sintering: 1375.degree., 1410.degree. or 1450.degree. C. 
Results before HIP 
Results: 
______________________________________ 
Sintering temperature 
1375.degree. C. 
1410.degree. C. 
1450.degree. C. 
Type of cobalt 
P1 F P1 F P1 F 
______________________________________ 
Porosity A02 A08 A02 A04 A02 A03 
Cobalt lakes* s N s N s N 
______________________________________ 
s = a few 
N = numerous 
*The average number of cobalt lakes was determined by counting (in an 
optical microscope) the lakes on ten optical fields at a magnification of 
1500 times and taking the average. 
d) Cobalt: 3% by weight 
Milling: 14 hours 
Results after HIP 
The HIP treatment consists in putting the samples sintered during the 
previous experiment in a HIP furnace at 1350.degree. C. for 2 hours under 
100 MPa (atmosphere =argon) 
Results: 
______________________________________ 
Sintering temperature 
1375.degree. C. 
1410.degree. C. 
1450.degree. C. 
Type of cobalt 
P1 F P1 F P1 F 
______________________________________ 
Porosity A01 A01 A01 A01 A01 A01 
Cobalt lakes s N O N O N 
______________________________________ 
s = a few 
N = numerous 
O = none 
These tests show clearly, that all other factors being equal, the use of 
cobalt powder according to the present invention is beneficial in 
,comparison with the use of a conventional cobalt powder since it results 
in a decrease of porosity and of the number of cobalt lakes. 
EXAMPLE 2 
Two laboratory scale batches of cemented carbide powder were made using the 
same batch of tungsten carbide, this batch having an average particle size 
of about 1 .mu.m as measured by the Fisher sub-sieve sizer method. In 
grade A, 6% by weight of conventional hydrogen-reduced cobalt powder was 
added and in grade B, 6% by weight of ultra-fine spherical cobalt powder 
of the present invention was added. The same small addition of chromium 
carbide powder was added to each grade. A fairly intense degree of milling 
was given to each grade by milling 1 kg of powder with 15 kg of milling 
bodies in a liquid for 13.5 hours in a rotary mill. Compacts were made 
from the dried cemented carbide powders and sintered, in close proximity 
with each other, under vacuum at a range of temperatures. Following 
sintering, microsections were prepared and the porosity levels were 
assessed by comparison with standard micrographs according to method ISO 
4505. The binder phase distribution was assessed by an arbitrary method. 
The specimens were first etched for 4 minutes at room temperature in 
Murakami's reagent and examined under an optical microscope at a 
magnification of 1500x. The average number of "cobalt lakes" pre, sent in 
a field of view was assessed by counting the number observed in 10 fields 
and dividing the total count by 10. Cobalt lakes are regions of binder 
phase, typically from 2-10 .mu.m in diameter, which occur when the 
sintering temperature was inadequate. The results obtained were as 
follows: 
______________________________________ 
Sintering temperature 
Microporosity 
Co lakes per field 
______________________________________ 
A 1450.degree. C. 
A02 0 
B 1450.degree. C. 
A00 0 
A 1410.degree. C. 
A02 4.9 
B 1410.degree. C. 
A00 0 
A 1360.degree. C. 
A08 &gt;200 
B 1360.degree. C. 
A02 5.6 
______________________________________ 
From the above results it can be seen that the use of the ultra-fine 
spherical cobalt powder in grade B had a marked effect on the level of 
microporosity and binder phase distribution, especially at the lowest 
sintering temperature employed. As well as permitting a lower sintering 
temperature to be employed, the use of ultra-fine spherical cobalt powder 
confers an improved degree of tolerance to temperature variations within 
the sintering furnace. 
EXAMPLE 3 
Two laboratory scale batches of cemented carbide powder were made using the 
same batch of tungsten carbide. This batch having a particle size of about 
40 .mu.m according to the Fisher sub-sieve sizer method. The true particle 
size was, however, approximately 15 .mu.m, the higher Fisher value being 
due to .agglomeration. In grade C, 6% by weight of conventional cobalt 
powder was added and in grade D, 6% of ultra-fine spherical cobalt powder 
of the present invention was added. No other carbides were added. A 1 kg 
charge of cemented carbide powder was milled with 5 kg of milling bodies 
and a liquid for 13.5 hours in a rotary mill. Compacts were made from the 
dried cemented carbide powders and sintered, in close proximity to each 
other, under vacuum at a range of temperatures. Following sintering, 
microsections were prepared and the porosity levels assessed according to 
the method detailed in ISO 4505. The results obtained were as follows: 
______________________________________ 
Grade Sintering temperature 
Microporosity 
______________________________________ 
C 1520.degree. C. 
A02 
D 1520.degree. C. 
A00 
C 1450.degree. C. 
A06 
D 1450.degree. C. 
A02 
C 1410.degree. C. 
A08 
D 1410.degree. C. 
A02 
C 1360.degree. C. 
&gt;A08 
D 1360.degree. C. 
A06 
______________________________________ 
The above results illustrate that a marked reduction in porosity levels was 
achieved using ultra-fine spherical cobalt powder. Thus, lower sintering 
temperatures may be employed and again an improved degree of tolerance to 
temperature variation within a furnace change is conferred. 
EXAMPLE 4 
Anvils for the 60 mm diamond production system have been tested according 
to the performance represented as life length in diamond production. The 
anvils were manufactured in three different grades of hard metal and 
marked with random numbers prior to the testing. The performance test was 
applied in a diamond production plant during "normal" working conditions 
whereas the results were reported with life lengths in comparison to 
presently used anvils. All anvils have a core consisting of a small amount 
(2%) of eta-phase in the structure. 
The anvils of grade A were manufactured according to the conventional 
production route of cemented carbide and were used as a reference in the 
test. The anvils were produced as described in Example 1 with 6% by weight 
of conventional hydrogen-reduced cobalt and a small addition of chromium 
carbide. The sintering temperature was 1450.degree. C. and the cemented 
carbide had a microporosity of A02. The microstructure did not show any 
cobalt lakes. 
The anvils of grade B had a similar composition as described for anvils of 
grade A without the chromium carbide content. The anvils were subjected to 
a hot isostatic pressing process at 4 MPa and 1410.degree. C. instead of 
standard sintering. No microporosity was obtained in the microstructure 
and 5.2 cobalt lakes per field were presented from microscopic examination 
of the cemented carbide. The microstructure was even and no influence of 
discontinuous or local grain growth could be seen. 
The anvils of grade C had a composition according to the present invention 
as described in Example 1 without the chromium carbide content. The anvils 
were subjected to a hot isostatic pressing procedure with the same 
conditions as for the anvils of grade B. The microstructure examination of 
the cemented carbide did not show any microporosity (A00) or cobalt lakes. 
The structure was even without any influence of discontinuous grain 
growth. 
The .alpha.-phase (WC) in the microstructure of the three grades of anvils 
had a mean grain size of about 1.2 .mu.m. 
The performance results were reported in actual number of pressings per 
anvil and scaled in a performance ranking. Each hard metal grade was 
represented by six anvils. 
Results: 
______________________________________ 
Performance/ 
Anvil No Number of pressings 
Rank 
______________________________________ 
Grade A: 
1 299 D 
2 99 E 
3 50 F 
4 921 A 
5 384 C 
6 50 F 
AVERAGE 300 C 
Grade B: 
1 568 C 
2 289 D 
3 270 D 
4 580 C 
5 602 B 
6 430 C 
AVERAGE 456 C 
Grade C: 
1 702 B 
(still in use) 
2 1399 A 
3 608 B 
4 592 C 
5 820 B 
6 906 A 
AVERAGE 837 B 
______________________________________ 
The results of grade A were uneven and the anvils with the low numbers of 
pressings had cracks in the top of the anvils. Grade B had a better 
performance but got the same ranking level as grade A. Three anvils had 
small cracks in the top surface. Grade C had the best performance ranking 
in the test and the best pressing behavior of all anvils. Obviously the 
anvils according to the invention had the most optimized hardness and 
toughness behavior due to a well dispersed cemented carbide matrix and a 
narrow grain size distribution of .alpha.-phase. 
EXAMPLE 5 
A coarse-grained tungsten carbide with a grain size of 18 .mu.m in the 
as-supplied state was used to produce test batches of very coarse cemented 
carbide for concrete and asphalt cutting tools. 
Cemented carbide with low cobalt content and very coarse grain size is 
needed to achieve optimum combination of toughness to wear resistance 
properties together with maximum thermal fatigue crack resistance. 
The same procedure as in Example 3 was used except for that the milling 
time was reduced to 9.5 hours. 
Grade X was produced with 6% of conventional cobalt and grade Y with 0.3 of 
ultra-fine spherical cobalt powder. Sintering was performed at 
1520.degree. C. in vacuum. Grade X showed a porosity level of A06, B06 
plus 8 pores of 25 .mu.m, and had to be HIP'd. Grade Y was fully dense 
with maximum porosity of A02, due to the effective and uniform reduction 
of the WC grains together with excellent mixing of the spherical cobalt 
with the tungsten carbide grains. 
The metallographical analysis showed as follows: 
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Grade X Grade Y 
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Grain size mean value 
7 .+-. 4 .mu.m 7 .+-. 1.5 .mu.m 
maximum size 18 .mu.m 10 .mu.m 
minimum size 1.8 .mu.m 5 .mu.m 
structure uneven with 10-15 cobalt 
even 
lakes of 10-20 .mu.m 
hardness (HV3) 
1215 1205 
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Road planing tips were made from the two test batches and were compared 
with a conventional grade, Z with 8 w/o Co, 5 .mu.m WC grains and a 
hardness of 1200 HV3. Point attack tools from the three grades were made, 
and they were geometrically identical with the carbide tips (9 mm, length 
18 mm with a conical top) brazed at the same time. 
The test was made in hard concrete with an Arrow CP 2000 road planing 
machine. 
Drum diameter: 1 m; drum width: 2.2 m 
Toolpick speed: 2.0 m/s; cutting depth: 25 mm 
180 tools, 60 per grade, were evenly distributed throughout the drum. 
Test result (mean value of 50 tools) 
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Wear Fractured 
Grade mm height reduction 
carbide (no of pcs) 
Rank 
______________________________________ 
X 5.3 8 2 
Y 4.8 1 1 
Z 8.1 7 3 
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EXAMPLE 6 
Buttons for roller bits with diameter 12 mm having a multiphase structure 
were produced from a small production batch. The average particle size of 
the WC was 3.5 .mu.m and the nominal cobalt content was 13.5% by weight. 
The added cobalt was ultra-fine spherical cobalt powder of the present 
invention with a Fisher grain size of 0.3 .mu.m. Compacts of the cemented 
carbide powder were sintered at 1340.degree. C. Corresponding buttons were 
produced with the same production process parameters except for the 
sintering temperature which was 1380.degree. C. These buttons originating 
from a cemented carbide powder blending with conventional cobalt powder 
with a Fisher grain size of 1.4 .mu.m. All buttons were thermally treated 
in a carburizing atmosphere for 2 hours. In the following examination of 
the microstructure of buttons from the two batches, it could be seen a 
multiphase structure with a core that contained eta-phase surrounded by a 
surface zone of a cemented carbide free of eta-phase having a low content 
of cobalt at the surface and a higher content of cobalt next to the 
eta-phase "core". 
Microprobe studies of the microsections gave the following results: 
Grade A (with ultra-tine cobalt): 
Eta-phase core (5.0 ram) 
mean grain size,, of eta-phase: 4.1 .mu.m 
mean cobalt content: 11.5 weight-% 
Cobalt "rich" zone (width 1.5 mm) 
mean cobalt content: 14.2 weight-% 
Cobalt "depleted" zone (width 2.0 mm) 
mean cobalt content: 10.0 weight-% 
Grade B (according to prior art with conventional cobalt) 
Eta-phase core (7.0 .mu.m) 
mean grain size, of eta-phase: 4.8 
mean cobalt content: 11.5 weight-% 
Cobalt "rich" zone (width 1.0 mm) 
mean cobalt content: 15.3 weight-% 
Cobalt "depleted" zone", (width 1.5 mm) 
mean cobalt content: 8.7 weight-% 
No porosity could be seen in the surface zone. It is obvious that buttons 
prepared according to the invention gave a more distinct multi-phase 
structure with a higher cobalt gradient in the surface zone. 
EXAMPLE 7 
Wear and toughness tests were performed with roller bits in an open-cut 
copper mine. The roller bits were of type 9 7/8" CS consisting of three 
roller cones with spherical buttons. The diameter of the buttons was 12 
mm. For one roller bit, the buttons according to the invention were placed 
in all positions of the buttons in row 1. Three types of roller bits were 
used in the test. 
Bit A: Buttons according to Example 6 were placed as above and in the 
excepted positions, comparative buttons with the same composition 
according to the prior art. 
Bit B: Comparative buttons of Example 6 according to prior art in all 
positions. 
Bit C: Standard cemented carbide with the same composition as in Example 6 
but being free of eta-phase and without the multi-phase structure. 
Drill rig: 1 pce. BE 45R 
Feed: 0-60000 lbs. 
Rpm: 60-85 
Hole depth: 18-20 m 
Type of rock: Biotite gneiss, mica schist. 
Result: 
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Drilled Drilling Depth 
Grade Meters Index (m/h) Index 
______________________________________ 
A 1900 160 18 140 
B 1650 140 16 120 (prior art) 
C 1170 100 14 100 (prior art) 
______________________________________ 
The grade according to the invention has obtained longer life length as 
well as greater drilling rate. 
The wear of the buttons was measured at 800 drilled meters. 
Results: 
Grade A: 
Row 1: Buttons according to the invention Average wear 3.0 mm 
Row 2: Average wear 2.8 mm 
Row 3: Average wear 2.5 mm 
The wear profile gave a self-sharpening effect due to a wear looking like 
"egg shells". The effect was most marked at row 1. One button was missing 
in row 1. 
Grade B: 
Row 1: Average wear 3.2 mm 
Row 2: Average wear 2.8 mm 
Row 3: Average wear 2.4 mm 
The wear of the buttons was of "egg shells"-type. From row 1 three buttons 
from one roller cone and two respectively one from the other two were 
missing. Two buttons were missing in row 2. 
Grade C: 
Row 1: Average wear 3.6 mm 
Row 2: Average wear 3.0 mm 
Row 3: Average wear 2.6 mm 
From row 1 five buttons from one roller cone and four respectively one from 
the other two were missing. The penetration rate was slow at 800 drilled 
meters. 
This test gave surprisingly good results for the roller bit attached with 
buttons made according to the invention. The penetration of the roller bit 
was also very good. 
EXAMPLE 8 
From a 91.5:8.5 WC (2 .mu.m)/Co (1.2 .mu.m) powder mixture, granules 
(hereafter referred to as basic granules) were prepared according to the 
conventional technique. Then a sufficient amount of cobalt (polyol-type 1 
.mu.m) was added to the granules until the respective proportions of WC/Co 
reached 88:12. After mixing for 30 minutes in a Turbula-type mixer, the 
resulting mixture (`modified granules`) was tested for flowability 
according to ISO 4490 with the following results: 
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Time/100 g, s 
______________________________________ 
Basic Granules 53 
Modified Granules 
46 
______________________________________ 
After compaction and sintering, a cemented carbide was prepared with the 
basic granules and the modified granules. The Vickers hardness was 
determined with the following result: 
______________________________________ 
HV50 
______________________________________ 
Basic Granules 1455 
Modified Granules 1300 
______________________________________ 
As expected, the hardness of the cemented carbide with the modified 
granules is lower than that of the basic cemented carbide in view of the 
higher cobalt content. The structure, however, of the carbide obtained 
with the modified granules is satisfactory. 
The principles, preferred embodiments and modes of operation of the present 
invention have been described in the :foregoing specification. The 
invention which is intended to be protected herein, however, is not to be 
construed as limited to the particular forms disclosed, since these are to 
be regarded as illustrative rather than restrictive. Variations and 
changes may be made by those skilled in the art without departing from the 
spirit of the invention.