Ceramic-based substrate for coating diamond and method for preparing substrate for coating

Ceramic-based substrate for coating, e.g., diamond has a basic irregularities surface having a surface roughness Rz of 2 to 20 .mu.m, with Rz at angle regions of 40% or more of that for other than the angle regions. The basic irregularities surface has micro-sized irregularities on an order of crystal grains constituting the uppermost surface (0.5 to 10 .mu.m), forming dual irregularities surface structure. Coating layer engages with surface irregularities to secure firm adhesion at the cutting edge. WC-based cemented carbide is used as substrate and N-containing surface layer is formed by heat treatment to form the surface irregularities.

FIELD OF THE INVENTION 
This invention relates to a ceramic-based substrate for coating and, more 
particularly, to a ceramic-based substrate for coating thereon of a hard 
film, such as a diamond film or a cubic boron nitride (CBN) film. The 
ceramic-based substrate of the present invention, on which the hard film, 
such as the diamond or CBN film, is coated, may be used as machining 
tools, such as cutting tools (inserts), end mills, cutters or drills, 
wear-resistant members, electronic members, such as heat sinks. 
BACKGROUND 
Related Art 
With diamond-coated hard materials comprising a substrate and diamond 
coated thereon, the diamond coating layer has only a low adhesion strength 
with respect to the substrate, such that the diamond coating layer tends 
to be peeled off from the substrate. Various techniques, such as 
exemplified hereinbelow, have hitherto been proposed in order to improve 
the adhesion strength of the diamond coating layer on the substrate. 
In JP Patent KOKAI Publication No. 1-246361 (JP-A246861/89) there is 
disclosed a sintered alloy having a specified coating film formed on a 
heated surface of a sintered alloy having a specified composition. 
In JP Patent KOKAI PUblication No. 4-281428 (JP-A231428/92), there is 
disclosed a method for producing a machining tool comprising secondary 
sintering of a cemented carbide (superhard alloy) tool of a particular 
composition under specified conditions followed by chemical etching and 
ultrasonic grinding/polishing for forming a diamond coating layer. 
In JP Patent KOKAI Nos. 4-263074 (JP-A-263074/92) and 4-263075 
(JP-A-263075/92), there is disclosed a hard material comprising a 
substrate presenting specified surface irregularities and a diamond 
coating layer formed thereon. 
Among the techniques preceding the above techniques, there are those 
described in JP KOKAI Patent Publication No. 54-87719 (JP-A-87719/79) and 
No. 58-126972 (JP-A-126972/83) corresponding to JP Patent KOKOKU 
Publication No. 62-7267. 
In "Powder and Powder Metallurgy", vol. 29, No. 5, pages 159 to 163, there 
is report on the formation of a hard layer on the surface of a 
WC--.beta.--Co alloy, where .beta. is a WC--TiC solid solution. Thus it is 
stated therein that, if the alloy is heated at 1673 K in N.sub.2 at 5.1 
kPa (5.times.10.sup.-2 atmosphere), a hard layer presenting sharp surface 
irregularities is formed; such hard layer is formed at a N.sub.2 pressure 
of not lower than about 0.7 kPa (about 7.times.10.sup.-3 atmosphere); and 
that the higher the N.sub.2 pressure and the longer the heating time 
employed, the coarser become the grains (.beta.(N) grains) of the 
WC--TiC--TiN solid solution and the more outstanding become the surface 
irregularities, with formation of Co pools on the surface region. 
Problems to be Solved by the Invention 
Based on the eager investigations in the art by the inventors, the 
following points have turned out. 
By the above related-art techniques, the diamond coating layer may be 
bonded to the substrate with as yet an insufficient adhesion strength, 
such that the diamond coating layer tends to be peeled off from the 
substrate and hence the resulting hard material is insufficient in 
durability. Thus the demand is raised for a substrate for coating which 
assures sufficient tight bonding properties with respect to a hard coating 
film, such as a diamond film, such that the resulting coated substrate may 
be employed for a machining toot used under extremely severe conditions, 
such as a tool used for milling an Al alloy containing a large quantity of 
Si. However, the conventional substrates for coating exhibit only poor 
bonding properties. 
In addition, the method described in "Powder and Powder Metallurgy" is not 
disclosed as being a method for the preparation of a substrate coated by a 
diamond film at all, such that it is not clear whether or not the method 
can be used for satisfactorily coating a diamond film on the substrate. 
Besides, since heating is performed under a reduced pressure, heating 
conditions are difficult to control to render it difficult to produce the 
substrates for coating in large quantities. 
SUMMARY OF THE DISCLOSURE 
It is an object of the present invention to provide a novel substrate for 
coating, a coated substrate and a method for producing same, which can 
overcome the drawbacks of the conventional techniques. 
According to the present invention, the above object may be accomplished by 
the following substrate for coating, coated substrate and method for 
producing the substrate for coating. 
(i) A ceramic-based substrate for coating having a surface presenting basic 
surface irregularities having a surface roughness Rz of 2 to 20 .mu.m. 
(ii) A ceramic-based substrate for coating having a surface presenting 
basic surface irregularities having a surface roughness Rz of 2 to 20 
.mu.m, with surface roughness Rz at angle regions being 40% or more of a 
surface roughness Rz at the regions other than the corner regions. 
(iii) A coated substrate comprising the above ceramic-based substrate 
coated with a hard film, preferably a diamond coating film. 
iv) A method for producing a substrate for coating comprising 
(a) providing a WC-based cemented carbide piece mainly composed of WC, 
(b) heat-treating said cemented carbide piece at a temperature not lower 
than a temperature at which a liquid phase of said WC-based cemented 
carbide piece is generated and not higher than its sintering temperature 
under a normal-pressure atmosphere containing a N.sub.2 gas of 0.05 to 5 
vol %, and 
forming a N-containing surface layer presenting surface irregularities on a 
surface of said WC-based cemented carbide piece. 
(v) A method for producing a substrate for coating comprising 
(a) providing an angle region of a WC-based cemented carbide piece, mainly 
composed of WC, with a rounded (or chamfered) profile in which a profile 
line on the cross-section of the angle region comprises a curve having a 
radius of curvature R of not less than 0.005 mm, 
(b) heat-treating the WC-based cemented carbide piece from the step (a) at 
a temperature not lower than a temperature of generating a liquid phase of 
said WC-based cemented carbide and lower than its sintering temperature, 
under a normal-pressure atmosphere containing 0.05 to 5 vol % of a N.sub.2 
gas, and 
(c) forming a N-containing surface layer presenting surface irregularities 
on a surface of said WC-based cemented carbide piece. 
The surface of the ceramic substrate for coating presenting surface 
irregularities (protrusions and recesses) has a surface presenting the 
basic surface irregularities (may be referred to as "basic irregularity 
surface" herein) which preferably has micro-sized surface irregularities 
having a size on an order of the size of crystal grains making up the 
outermost substrate surface (typically of 0.5 to 10 .mu.m) and, more 
preferably, has micro-sized irregularities 1 to 5 .mu.m and smaller than 
the roughness of the basic irregularities, relative to the basic 
irregularity surface, resulting in a dual-irregularity-surface structure. 
These micro-sized irregularities extend in a direction not only normal, but 
also obliquely or further transversely (parallel) with respect to the 
basic irregularity surface. 
In the following, meritorious effects of the invention will be summarized. 
Since the ceramic-based substrate for coating according to the present 
invention has the above-mentioned specified basic surface irregularities, 
a hard coating layer, such as a diamond layer, formed on its surface, is 
bonded strongly to the substrate surface without the risk of peeling-off. 
The method for producing a substrate for coating according to the present 
invention comprises 
(a) providing a WC-based cemented carbide piece mainly composed of WC, 
(b) heat-treating said cemented carbide piece at a temperature not lower 
than a temperature at which a liquid phase of said WC-based cemented 
carbide piece is generated and not higher than its sintering temperature 
under a normal-pressure atmosphere containing a N.sub.2 gas of 0.05 to 5 
vol %, and 
(c) forming a N-containing surface layer presenting surface irregularities 
on a surface of said WC-based cemented carbide piece. 
Therefore, when a hard coating layer, such as a diamond layer, is formed on 
the surface of the N-containing surface layer presenting surface 
irregularities, the coating layer is strongly bonded to the surface layer 
to provide a substrate for coating unsusceptible to peeling-off. 
The ceramic-based substrate for coating according to the present invention 
has the above-mentioned (basic surface irregularities) and the surface 
roughness Rz at the angle region amounts to not less than 40% of the 
surface roughness Rz of the region other than the angle region. Thus the 
hard coating layer, such as a diamond layer, formed on its surface becomes 
strongly affixed to the substrate surfaces without the risk of 
peeling-off. 
The method for producing the substrate for coating according to the present 
invention comprises 
(a) chamfering an angle region of a WC-based cemented carbide piece, mainly 
composed of WC, so that the profile line on the cross-section of the angle 
region includes a curve having a radius of curvature R of not less than 
0.005 mm, 
(b) heat-treating the WC-based cemented carbide piece from the step (a), at 
a temperature not lower than a temperature at which a liquid phase of said 
WC-based cemented carbide piece is generated and not higher than a 
sintering temperature under a normal-pressure atmosphere containing a 
N.sub.2 gas of 0.05 to 5 vol %, and 
(c) forming a N-containing surface layer presenting surface irregularities 
on a surface of said WC-based cemented carbide piece. 
Consequently, a hard coating layer, such as a diamond layer, formed on the 
surface of the N-containing surface layer presenting surface 
irregularities, to produce a substrate for coating, is strongly bonded to 
the surface layer without the risk of peeling-off. 
Thus it is possible with the present invention to produce any of a variety 
of machining tools, wear resistant members or electronic members which is 
not susceptible to peeling-off of hard coating layers, such as diamond 
layers, and which may be used for an extended period of time. 
SUMMARY OF PREFERRED EMBODIMENTS 
Preferably, the basic irregularity surface has an engaging ratio of 1.2 to 
2.5 and an amplitude of the irregularities of 2 to 20 .mu.m. 
Also preferably, the basic irregularity surface has a surface roughness 
(Rz) of 3 to 10 .mu.m measured on components of the basic surface 
irregularities at a period of 25 .mu.m or less. 
Preferably, the ceramic-based substrate for coating is adapted for being 
coated with diamond. Also preferably, the ceramic-based substrate for 
coating comprises (or is made up of) a main body of a ceramic-based 
substrate and at least one coating layer formed on the main body, wherein 
a coating layer having the dual irregularity surface structure constitutes 
an outermost layer. 
Preferably, the main body of the ceramic based substrate is formed of a 
WC-based cemented carbide (superhard alloy) mainly composed of WC and 
containing Ti with or without Ta, and at least one of Co and Ni. 
Preferably, the coating layer is mainly composed of at least one of a 
W--Ti--C--N solid solution and a W--Ti--Ta--C--N solid solution. 
Preferably, the hard film on the substrate for coating is formed of 
diamond. 
The above method for producing the ceramic-based substrate for coating 
preferably further comprises: 
forming a N-containing surface irregularity layer as a basic irregularity 
surface having a surface roughness Rz of 2 to 20 .mu.m on the surface of 
the WC-based cemented carbide piece. 
Preferably, a N-containing surface layer presenting dual surface 
irregularities i.e., the dual-irregularity surface structure is formed on 
the surface of the WC-based cemented carbide piece. The dual irregularity 
surface structure comprises the basic irregularity surface and micro-sized 
surface irregularities formed thereon with sizes of 0.5 to 10 .mu.m 
approximately corresponding (or equal) to those of crystal grains making 
up the uppermost surface, more preferably, of a size 1 to 5 .mu.m and 
smaller than the roughness of the basic irregularity surface. 
Preferably, there is formed a N-containing surface layer having the basic 
irregularity surface with an engaging ratio of 1.2 to 2.5 and an amplitude 
of irregularities of 2 to 20 .mu.m on the surface of the WC-based cemented 
carbide piece. 
Preferably, there is formed a N-containing surface layer having basic 
irregularity surface which has a surface roughness Rz of 3 to 10 .mu.m for 
components having a period of 25 .mu.m or less, on the surface of the 
WC-based cemented carbide piece. 
Preferably, a cemented carbide piece mainly composed of WC and containing 
Ti with or without Ta, and at least one of Co and Ni is used as the 
WC-based cemented carbide piece. 
Preferably, there is formed a N-containing surface layer having the basic 
irregularity surface mainly composed of at least one of a W--Ti--C--N 
solid solution and a W--Ti--Ta--C--N solid solution. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The "engaging ratio" herein means a ratio of a length of the irregular 
cross-sectional profile of the irregular surface (the path length of a 
curve constituting the irregular cross-sectional profile of the basic 
irregularity surface) divided by a linear distance length of the irregular 
cross-section (the length of a straight line interconnecting both ends of 
the cross-sectional profile). The "amplitudes" (of fluctuation) means the 
least value of a distance between two parallel lines inscribing the 
cross-sectional profiles (i.e., tip lines drawn at the highest protrusion 
and the lowest recess) of the irregular surface. 
With the ceramic-based substrate for coating according to the present 
invention, if the surface roughness Rz of the basic surface irregularities 
is less than 2 .mu.m, adhering properties cannot be improved, whereas, if 
it exceeds 20 .mu.m, the substrate is lowered in strength. Since the 
surface roughness Rz of the angle (or corner) regions is 40% or more of 
the surface roughness Rz of the regions other than the angle regions, the 
coating film applied on the substrate may hardly be peeled off. The 
surface roughness Rz of the regions other than the angle regions means the 
surface roughness Rz of regions spaced apart from the angle regions and 
preferably the surface roughness Rz of a central portion of the major 
surface of the ceramic-based substrate for coating. 
If the micro-sized irregularities as contrasted to the basic irregularity 
surface as a reference surface are of a size of 0.5 .mu.m or more, the 
hard film, such as the diamond film, can be adhered more strongly when 
deposited on the substrate surface. However, the bonding property superior 
to those with the sizes of the micro-sized irregularities less than 10 
.mu.m cannot be obtained even if the micro-sized irregularities are of 
sizes exceeding 10 .mu.m. The surface roughness Rz is defined by the 
average roughness of ten points as prescribed in JIS B 0601. 
If the engaging ratio is less than 1.2 or the amplitude of the surface 
irregularities is less than 2 .mu.m, the effects in improving the adhering 
properties tend to be lowered, whereas, if the engaging ratio exceeds 2.5 
or the amplitude of the basic irregularity surface exceeds 20 .mu.m, the 
substrate is lowered in strength and, if the coated substrate is used as a 
machining (or cutting) tool, the edge shape of the tool can hardly be 
maintained. More preferably, the engaging ratio is 1.3 to 2.0 and the 
amplitudes of the surface irregularities are 5 to 10 .mu.m. 
As for the basic irregularity surface, if the surface roughness Rz of the 
components having a period of 25 .mu.m or less is less than 3 .mu.m, the 
effect of the irregular surface in improving tight bonding properties 
tends to be lowered. Conversely, if the surface roughness exceeds 10 
.mu.m, the substrate tends to be lowered in strength and, if the coated 
substrate is used as a cutting tool, the cutting edge shape of the tool 
can hardly be maintained. More preferably, the surface roughness Rz is 5 
to 8 .mu.m. 
The reason for setting the surface roughness Rz of the components of 
irregularities to have a period not more than 25 .mu.m is that the 
components of the irregularities having the period of longer than 25 .mu.m 
are not particularly effective in improving the engaging (or fitting) 
power. 
The surface roughness Rz of the components of the irregularities having the 
period of not more than 25 .mu.m for the basic irregularity surface is 
found by measuring the surface roughness of the basic irregularity surface 
using a non-contact type three-dimensional shape analyzer, such as RD-500 
type manufactured by DENSHI KOGAKU KENKYUSHO K. K., Fourier transforming 
the measured waveform of the irregularities, filtering off components 
having a period exceeding 25 .mu.m, and measuring the surface roughness Rz 
on the waveform of the irregularities obtained by inverse Fourier 
transformation of the resulting waveform. 
It is noted that only those components having longer periods can be 
measured using a customary contact type surface roughness meter, a 
contactor of which has an tip radius of 5 to 10 .mu.m, while it is not 
possible to obtain any significant results of the surface state with Rz 
obtained with the contact type surface roughness meter. 
As for the method of the present invention, using a N.sub.2 gas in the 
ambient-pressure heat treatment atmosphere of less than 0.05 vol %, the 
N-containing irregular surface layer can be formed only with considerable 
difficulties because of the small quantity of N in the atmosphere. If the 
amount of N exceeds 5 vol %, the bonding phase (, e.g., Co) contained in 
the WC-based cemented carbide is precipitated on the surface in a larger 
quantity, thereby lowering the adhering property of the diamond coating 
layer. 
If the heat-treatment is carried out at a temperature lower than the 
temperature of generation of the liquid phase of the WC-based cemented 
carbide, the N-containing irregular surface has only insufficient surface 
irregularities such that a sufficient bonding property cannot be obtained 
on diamond coating. If the heat-treatment temperature exceeds the 
sintering temperature, the substrate tends to be lowered in its 
properties, such as strength, due to growth of grains making up the 
cemented carbide. By carrying out heat treatment under the ambient 
pressure, continuous processing by a tunnel furnace becomes feasible, 
besides processing by a batch furnace, with outstanding merits in cost and 
productivity. 
If the radius of curvature R of the chamfer is less than 0.005 mm, the 
degree of the N-containing surface irregularities formed at angle regions 
after heat treatment is lower than that at the regions other than the 
angle regions, for example, at a central part of the major surface of the 
substrate for coating. Thus the coating film is lowered in bonding 
properties. 
It is particularly preferred for a substrate used for producing cutting 
tools to chamfer the angle region of the WC-based cemented carbide 
employed in the method of the present invention so that the profile line 
on the cross-section of the angle region comprises a curve having a radius 
of curvature R of 0.005 to 0.10 mm. 
That is, the cutting tool has a cutting edge which is the angle region 
defined by an intersection of a face and a flank. If the profile line at 
the cross-section of the cutting edge extending at right angles to the 
rake face or clearance face (cross-section of the angle region) is formed 
by a curve or a straight line having the radius of curvature R less than 
0.005 mm, the substrate has a reduced thickness at the angle region so 
that the N-containing irregular surface layer produced by heat treatment 
is reduced in thickness and hence the surface irregularities become less 
outstanding than those of the regions other than the angle region. 
Consequently, the angle region of the coating layer tend to be inferior in 
the bonding property as compared to that of the regions other than the 
angle region. 
The reason the N-containing irregular surface is reduced in thickness in 
the angle regions by heat treatment is possibly thought that in case with 
the use of the WC-based cemented carbide mainly composed of WC and 
containing Ti, the Ti component is migrated as a result of the heat 
treatment in a smaller quantity due to the reduced thickness in the angle 
region. 
On the other hand, if the profile line includes a curve having a radius of 
curvature R exceeding 0.10 mm, the N-containing irregular surface layer 
produced by heat treatment has a sufficient degree of the surface 
irregularities, such that the bonding property between the angle regions 
and the coating layer is equivalent to those in the regions other than the 
angle region. However, if the angle region after coating are used as a 
cutting edge of the machining tool cutting chips tend to be welded due to 
excess increase in She cutting resistance, thus producing only a rough 
finishing state of a workpiece being machined. 
The angle region is shaped to the above-mentioned chamfered profiled shape 
by honing, such as round honing. 
The ceramic-based substrate herein means a hard substrate which is mainly 
composed of an ultra-hard ceramic material, such as carbides, nitrides, 
borides, composite compounds thereof, with or without oxides, or metal 
compounds and which is basically produced by sintering. The hard substrate 
includes cemented carbides (superhard alloy) or cermets composed mainly of 
carbides of high-melting metals and having a metal phase as a bonding 
phase. As for the basic irregularity surface is defined by a surface 
having a mean roughness of ten points as prescribed in JIS B 0601 in a 
range of 2 to 20 .mu.m. The ambient pressure means preferably 0.5 to 1.5 
atmosphere. 
Certain Preferred Embodiments 
Ceramic-Based Substrate for Coating 
The ceramic-based substrate for coating according to the present invention 
may be made up of a main substrate body and a coating layer thereon. One 
or more coating layer(s) may be provided. The coating layer is preferably 
engaged to the main substrate body. 
The main substrate body is preferably a hard material of cemented carbide 
or the like and may comprise a WC--Co based cemented carbide containing 
TiC with or without TaC. If TaC is contained in the hard material, Ta may 
be replaced in part or in its entirety by at least one of V, Zr, Nb and 
Hf. 
The coating layer is preferably formed of at least one of a W--Ti--C--N 
solid solution and a W--Ti--Ta--C--N solid solution. 
Coated Substrate 
The coated substrate according to the present invention comprises the 
ceramic-based substrate of the present invention and a hard coating film 
coated thereon. Diamond or CBN may be used as a material for the hard 
coating film. 
Method for Producing a Substrate for Diamond Coating 
The WC-based cemented carbide is composed mainly of WC. Other components 
include preferably Ti, with or without Ta, and at least one of Co and Ni 
as a bonding phase. As a preferred composition of the WC-based cemented 
carbide, Ti with or without Ta amounts to 0.2 to 20 wt %, preferably 0.5 
to 10 wt % and more preferably 1 to 5 wt %, calculated as carbide, and at 
least one of Co and Ni amounts to 2 to 15 wt %, preferably 3 to 10 wt % 
and more preferably 4 to 7 wt %. The alloy contains at least one of a 
W--Ti--C solid solution (.beta.-phase) and a W--Ti--Ta--C solid solution 
(.beta.t-phase). The .beta.-phase and the .beta.t phase are of a crystal 
grain size of preferably 0.5 to 10 .mu.m and more preferably 1 to 5 .mu.m. 
If the amount of Ti, calculated as carbide, is less than 0.2 wt % the 
N-containing irregular surface layer can be formed only with difficulties 
by heat treatment. Besides, the surface layer formed on heat treatment 
tends to be peeled off. The reason the surface layer tends to be peeled 
off is that the majority of the Ti component is migrated towards the 
surface by the heat treatment to form the W--Ti--C--N solid solution, that 
is the .beta. (N) phase, on the surface, with a result that the Ti 
component is separated from the other alloy component to deteriorate the 
state of engaging. If the amount of Ti, calculated as carbide, exceeds 20 
wt %, the substrate is already brittle prior to heat treatment. Besides, 
the substrate is increased in its coefficient of thermal expansion 
coefficient which becomes significantly different from that of the diamond 
with a consequence that a shearing stress is induced on a 
substrate-diamond film interface during cooling following diamond coating, 
thus possibly leading to peeling off of the diamond film. 
The above also accounts for the reason the upper limit of Ti and Ta, Ta 
being occasionally contained together with Ti, is set to 20 wt %. 
Meanwhile, Ta may be replaced entirely or in part by at least one of V, Zr, 
Nb and Hf insofar as the above-mentioned heat treatment remains not 
adversely affected. If the crystal phase of the above carbide is grown in 
size during sintering, the WC-based cemented carbide, obtained by densely 
sintering powders of WC, TiC, TaC and/or Co by powder metallurgy, is 
lowered in strength. Consequently, at least one of Cr and Mo, capable of 
suppressing the grain growth during the sintering, is contained in the 
composition, usually as a carbide, insofar as it does not adversely affect 
the heat treatment according to the present invention. 
If the amount of at least one of Co and Ni as the bonding phase is less 
than 2 wt %, the WC-based cemented carbide cannot be improved in density 
on sintering, such that the substrate becomes insufficient in its 
characteristics, such as strength, as demanded of the substrate. If the 
amount of Co and Ni exceeds 15 wt %, these components tend to be 
manifested on the substrate surface during the heat treatment or diamond 
film formation according to the present invention, thus occasionally 
adversely affecting the process of the diamond film formation. On the 
other hand, the difference in the coefficient of thermal expansion between 
the substrate and the diamond film becomes significant to lead to the 
peeling-off of the diamond film. 
If the mean grain size of the .beta.-phase or the .beta.t phase is less 
than 0.5 .mu.m, the N-containing surface layer appearing after the heat 
treatment is diminished in the irregularity, or the N-containing surface 
layer may not be engaged together sufficiently in the inner WC-based 
cemented carbide layer. If it exceeds 10 .mu.m, the engagingment may be 
insufficient, or the strength demanded to the WC-based cemented carbide 
prior to the heat treatment can occasionally not be obtained. 
In the case with the N-containing cemented carbide or cermet containing the 
.beta. (N) phase from the outset obtained by sintering with addition of 
N-containing powders, such as powders of TiN or TiC--TiN solid solution, 
or sintering in a nitrogen atom containing atmosphere, there may be 
occasions wherein surface irregularities can be produced with difficulty 
even through the heat treatment according to the present invention, or 
control of the state of the irregularities by the heat treatment 
atmosphere becomes difficult or impossible. 
For accurately controlling the N.sub.2 content in the atmosphere for heat 
treatment of the WC-based cemented carbide, a furnace used for the heat 
treatment is constructed using a refractory material not affecting the 
N.sub.2 content in the atmosphere. A furnace made of a refractory material 
such as BN should not be used. 
The preferred heat-treatment temperature for the WC-based cemented carbide 
is 1350.degree. to 1450.degree. C. The lower limit differs with the amount 
of carbon in the alloy or Co--Ni ratio. 
The heat treatment time represents a factor which most significantly 
influences the degree of the surface irregularities of the N-containing 
surface layer. The N-containing surface layer having arbitary 
irregularities may be formed by adjusting the heat treatment time. For 
producing the N-containing layer stably and efficiently, adjustment is 
made of the heat treatment temperature and the N.sub.2 content in the 
atmosphere. The heat treatment time is preferably set to 0.5 to 5 hours. 
The heat-treatment atmosphere contains 0.05 to and preferably 0.5 to 3 vol 
% at the ambient pressure, the balance being an inert gas, such as Ar. 
After forming the N-containing irregular surface layer in accordance with 
the method for producing the substrate for coating according to the 
present invention, re-heating (additional heat treatment) may be carried 
out in an inert atmosphere, such as an argon atmosphere, insofar as the 
bonding properties of the surface layer remain unaffected. In this manner, 
N may be released from the surface layer. 
As another method for producing the effect of having the uppermost surface 
freed of N, equivalent to that achieved by the above-mentioned re-heating 
method, a hard film of, e.g., TiC may be formed by any known method, such 
as CVD or PVD, to a thickness for which the surface properties of the 
irregular surface layer are not changed significantly. 
For diamond coating, the CVD method of contacting an excited mixed gas of a 
carbon source gas and a hydrogen gas may be employed. Above all, the 
microwave plasma CVD method is preferred as means allowing an accurate 
control of the synthesizing conditions. 
it is desirable for improving the engaging (or fitting) power that the 
conditions for synthesis of the diamond film are set so that in the 
initial stage, as many nuclei as possible are produced not only on surface 
protrusions but also in the inside of the surface recesses. Subsequently 
the film may be grown under the conditions that allow a higher rate and a 
satisfactory film strength. 
The diamond coating may be achieved in two steps for forming two or more 
coating layers. 
Now the present invention will be explained in more detail with reference 
to the Drawings and Examples.

EXAMPLES 
Example A 
As starting powders, WC powders and powders of the TiC--WC solid solution 
having a mean particle size of 2 .mu.m, TaC and Co powders having a mean 
particle size of 1 .mu.m, were prepared. These starting powders were mixed 
so that the proportions in Table 1, calculated as WC, TiC, TaC and Co, 
were obtained. The mixed powders were wet mixed, dried and press molded at 
a pressure of 147 MPa (1.5 ton/cm.sup.2) to a pressed powder mass, which 
was then sintered at 1400.degree.to 1450.degree.C. for one hour to produce 
sintered products, each having substantially the same composition as the 
above-mentioned mixed system. The sintered products were then ground on 
their surfaces to produce inserts (tips) each having a shape SPGN 120308 
as prescribed in the ISO standard. 
These inserts were charged into a carbon case and heat-treated, under the 
conditions shown in Table 2, using an electric furnace the portions of 
which exposed to elevated temperatures such as heater and insulator are 
all formed of carbon, thereby forming a modified surface layer having 
characteristics as shown in Tables 2 and 3. 
The resulting substrates having modified surface layers (sample Nos. 2 to 
40) and an insert not heat-treated (sample No. 1) were immersed in a 
solvent containing fine diamond powders having a mean particle size of 10 
.mu.m, suspended in a separated state therein, and processed with 
ultrasonic processing, for activating the insert surface. 
The inserts thus produced were placed in a micro-wave plasma CVD apparatus 
with a frequency of 2.45 GHz and were maintained for ten hours in a mixed 
plasma of H .sub.2 -2% CH.sub.4 heated to 850.degree. C. and set to a 
total pressure of 6666 Pa (50 Torr), for producing diamond coated 
machining inserts each having a film thickness of approximately 10 .mu.m. 
In the present experiment, the coating layer precipitated on the substrate 
surface was identified to be a diamond coating layer by analyses by the 
Raman spectroscopic method. 
Using these cutting inserts, machining tests were carried out under the 
following conditions. It is seen from Tables 2 and 3 that the 
diamond-coated inserts of the present invention exhibit superior 
characteristics, wherein the time permitting machining with satisfactory 
surface accuracy without peeling-off of the diamond film is long. As 
contrasted thereto, in the comparative Examples, the diamond film exhibits 
only a poor adhesion strength and hence tends to be peeled off, wherein 
the time permitting machining of the workpiece with satisfactory surface 
accuracy is short and the substrate occasionally suffers fracture (or 
chipping). 
Continuous Machining (machining an outer periphery of a rodlike workpiece 
having a diameter of approximately 150 mm and a length of approximately 
200 mm) 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 800 m/min 
feed: 0.15 mm/rev 
depth of cut: 0.5 mm 
______________________________________ 
intermittent machining: milling (machining the surface of a square plate of 
about 150.times.150 mm in size and about 50 mm in thickness) 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 600 m/min 
feed: 0.1 mm/tooth 
depth of cut: 0.5 mm 
______________________________________ 
In Tables 2 and 3, .alpha., .beta. and .gamma. stand for the crystal phases 
and denote the following 
.alpha.: WC 
.beta.: .beta. phase, .beta.t phase or .beta. (N) phase formed by solid 
solution of N in .beta.- or .beta.t-phase 
.gamma.: bonding phase composed mainly of Co and/or Ni The same holds for 
.alpha., .beta. and .gamma. in Table 5. 
The possible presence of the modified surface layer was checked by 
elementary analyses in a cross-sectional plane alone the substrate 
thickness as measured by the electron probe microanalysis (EPMA). If the 
Ti and/or Ta component is segregated near the surface and a portion 
entirely free of Co is found, the sample was determined "YES" to have the 
modified surface layer. On the other hand, if there is no difference 
between the surface and the inside in the dispersed state of the bonding 
phase containi ng Co or grains containing Ti and/or Ta, and a 
comparatively even state of dispersion is observed, the sample was 
determined "NOT" to be free of the modified surface layer. The same 
applies for Table 5. 
Electron Probe Microanalysis 
For each of the substrate of the present invention (sample No. 11) and the 
substrate of the Comparative Example (sample No. 1), elementary analyses 
were conducted in the cross-sectional plane of the substrates along the 
thickness by the electron probe microanalysis (EPMA). It was thus found 
that, with the substrate of the Comparative Example, the particles 
containing Ti and Ta (.beta.t phase) and the Co-containing bonding phase 
were dispersed substantially uniformly, with the substrate being of a 
structure free of the modified surface layer on its surface. Conversely, 
the inventive substrate was found to have a modified surface layer which 
contains Ti and Ta and which is completely free of Co. It was also found 
that the modified surface layer contained nitrogen (N). The results of the 
analyses are shown in FIGS. 5 and 7. 
Example B 
As starting powders, WC powders and powders of the TiC--WC solid solution 
having a mean particle size of 2 .mu.m, TaC and Co powders having a mean 
particle size of 1 .mu.m, were used. These starting powders were mixed so 
that the proportions in Table 4, calculated as WC, TiC, TaC and Co were 
obtained. The mixed powders were wet mixed, dried and press molded at a 
pressure of 147 MPa (1.5 ton/cm.sup.2) to a pressed powder mass, which was 
then sintered at 1400.degree. to 1500.degree. C. for one hour to produce 
sintered products each having substantially the same composition as the 
above-mentioned mixed system. The sintered products were then ground on 
their surfaces to produce inserts each having the shape SPGN 120308 as 
prescribed in ISO standard. 
These inserts were charged into a carbon case and heat-treated, under the 
conditions shown in Table 5, using an electric furnace the portions of 
which exposed to elevated temperatures such as heater and insulator are 
all formed of carbon, thereby forming a modified surface layer having 
characteristics-as shown in Table 5. 
The engaging ratio and the amplitude width were measured in the following 
manner. 
1) The state of irregularities of a photograph of the cross-section of the 
irregular surface as taken by SEM, was saved as image data, using an image 
processor LUZEX III manufactured by NIRECO KK. The data was that of a 
meandering curve. 
2) The total path length of the curve (defined as the length of the 
cross-section of the irregular surface) and the length of a straight line 
interconnecting both ends of the curve(defined as a straight line distance 
of the cross-section of the irregular surface) were measured. The length 
of the cross-section divided by the straight line distance of the 
cross-section was used as the "engaging ratio" The measured value of the 
straight line distance was approximately 200 .mu.m. 
3) The minimum value of the distance between two parallel lines inscribing 
the curve was measured by the above processor and was used as the 
"amplitude" or "width of amplitude". 
The surface roughness Rz of the components of the irregularities having the 
repeating period of 25 .mu.m or less was measured by the following 
non-contact manner. 
The SEM was fitted with a three-dimensional analyzer RD-500 manufactured by 
Yugen Kaisha DENSHIKOGAKU KENKYUSHO for measuring the surface state. With 
this analyzer, a backscattering electron detector of the SEM is split in 
four sections for measuring changes in the scattering direction of the 
electron beams produced by the surface state, and data analyses are 
conducted by a computer in order to permit three-dimensional shape 
measurement. In this manner, it becomes possible to measure micro-sized 
irregularities which was difficult to measure with a conventional 
contactor type analyzer used for measuring the surface state such as 
surface roughness because the contactor usually has the tip end radius on 
the order of 5 to 10 .mu.m. 
The waveform of the cross-section presenting irregularities was found from 
the resulting data of the surface profile and transformed by Fourier 
transformation. After filtering off of the components having the period 
exceeding 25 .mu.m and inverse Fourier transformation, the ten points mean 
roughness Rz as prescribed in JIS B 0601 was found of the resulting 
waveform of the irregularities. In this manner, the Rz value was obtained 
of the irregular components having the period of not more than 25 .mu.m. 
The surface roughness was measured using a contactor type surface roughness 
meter having a contactor with a tip end radius of 5 .mu.m, and the mean 
radius Rz of ten points was found of the irregular components having a 
relatively longer period. 
The resulting substrates having modified surface layers were immersed in a 
solvent containing fine diamond powders having a mean particle size of 10 
.mu.m, suspended in a separated state therein, and processed with 
ultrasonic processing, for activating the insert surface. 
The inserts thus produced were placed in a micro-wave plasma CVD 
device-having a carrier frequency of 2.45 GHz and were maintained for ten 
hours in a mixed plasma of H.sub.2 -2% CH.sub.4 heated to 850.degree. C. 
and set to a total pressure of 6666 Pa (50 Torr) to produce diamond coated 
machining inserts each having a film thickness of approximately 10 .mu.m. 
In the present experiment, the coating layer precipitated on the substrate 
surface was identified to be a diamond coating layer by analysis by a 
Raman spectroscopic method. 
Using these cutting inserts, machining tests were carried out under the 
following conditions. It is seen from Table 5 that the diamond-coated 
inserts of the present invention exhibit superior characteristics, with 
the time permitting machining with satisfactory surface accuracy without 
diamond film peeling-off being long. As contrasted threto, as for the 
comparative Example, the diamond film exhibits only a poor adhesion 
strength and hence tends to be peeled off, in which the time permitting 
machining of the workpiece with satisfactory surface accuracy being short 
and the substrate being occasionally fractured. 
Continuous Cutting (machining an outer periphery of a rod-like workpiece 
having the diameter of approximately 150 mm and a length of approximately 
200 mm) 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 1200 m/min 
feed: 0.15 mm/rev 
depth of cut: 0.5 mm 
______________________________________ 
Intermittent Cutting (machining of the surface of a square plate workpiece 
about 150.times.150 mm is size and about 50 mm in thickness) 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 800 m/min 
feed: 0.1 mm/tooth 
depth of cut: 0.5 mm 
______________________________________ 
Example C 
A sintered member formed of a material F shown in Table 1 was produced in 
the same way as in Example A and ground to cemented carbide inserts having 
a shape conforming to ISO standard SPGN 120308. The cutting edge of the 
insert was honed so that a profile line at the cross-section of the 
cutting edge in a direction perpendicular to the rake face includes a line 
or a curve having a radius of curvature R as shown in Table 6. These 
inserts were charged in a carbon casing having a thickness of 4 mm and an 
inside dimension 92 mm (diameter).times.31 mm. Using an electrical 
furnace, all the portions whereof exposed to elevated temperatures, such 
as heaters or insulators are formed of carbon, the inserts were 
heat-treated at 1375.degree. C. for three hours in a 1% N.sub.2 --Ar 
atmosphere at 0.1 MPa (1 atm) for producing a modified surface layer (a 
N-containing surface layer having surface irregularities). The state of 
the cross-section in a direction at right angles to the rake face of the 
cutting edge of the inserts, and the surface states, of sample numbers 53, 
56 and 58, among the inserts, are shown in FIGS. 14 to 16 and in FIGS. 17 
to 19, respectively. The distribution of the thickness and that of the 
surface irregularities of the modified surface layer are shown in Table 6. 
The above-mentioned honing was carried out using a "brush grinder" in which 
a liquid containing free diamond abrasive grains dispersed in oil is 
supplied to the inserts and a disc-shaped brush is rotated for contacting 
the liquid with the inserts. The operating conditions were set at a rpm of 
the brush of 300 to 600 rpm, a grade of the free diamond abrasive grains 
at #300 to #1000 and a processing time until the cutting end reached a 
pre-set radius of curvature of 1 to 10 minutes. 
The surface state of the workpiece was set in conformity to the following 
criteria depending on the surface roughness Rz of the workpiece (mean 
roughness of ten points as prescribed in JIS B0601): 
______________________________________ 
good Rz .ltoreq. 6 .mu.m 
acceptable 6 .mu.m &lt; Rz .ltoreq. 12 .mu.m 
bad Rz &gt; 12 .mu.m 
______________________________________ 
The preferred ranges of the machining time until film peeling-off are a 
range exceeding 60 minutes, more preferably exceeding 120 minutes, and a 
range exceeding 40 minutes, more preferably exceeding 70 minutes, for 
continuous cutting and for intermittent cutting, respectively. 
The inserts thus produced were placed in a microwave plasma CVD device 
having a carrier frequency of 2.45 GHz and were maintained for ten hours 
in a mixed plasma of 98 vol % H.sub.2 -2% CH.sub.4 heated to 850.degree. 
C. and set to a total pressure of 6666 Pa (50 Torr) for producing diamond 
coated cutting inserts each having a film thickness of approximately 10 
.mu.m. 
Using these cutting inserts, cutting tests were carried out under the 
following conditions. It is seen from Table 6 that the diamond-coated 
inserts of the present invention exhibit superior characteristics, with 
the time permitting machining with satisfactory surface accuracy without 
diamond film peeling-off being long, whereas, with the comparative 
Example, the diamond film exhibits only a poor adhesion strength and hence 
tends to be peeled off, with the time permitting machining of the 
workpiece with satisfactory surface accuracy being short and the substrate 
being occasionally fractured. 
Continuous Cutting (machining an outer periphery of a rod-like workpiece 
having the diameter of approximately 150 mm and a length of approximately 
200 mm). 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 1500 m/min 
feed: 0.15 mm/rev 
depth of cut: 0.5 mm 
______________________________________ 
Intermittent Cutting: milling (machining the surface of a square plate 
about 150.times.150 mm in size and about 50 mm in thickness)) 
______________________________________ 
workpiece: Al-18 wt % Si alloy 
cutting speed: 1000 m/min 
feed: 0.l mm/tooth 
depth of cut: 0.5 mm 
______________________________________ 
A scanning electron microscope (SEM) was fitted with a three-dimentional 
analyzer RD-500 manufactured by Yugen Kaisha DENSHI KOGAKU KENKYUSHO for 
measuring the surface state irregularities (surface roughness Rz). 
The waveform of the cross-section presenting irregularities was found from 
the resulting data of the surface profile and transformed by Fourier 
transformation. After filtering off of the components having the period 
exceeding 25 .mu.m and inverse Fourier transformation, substantially in 
the same manner as Example B, the ten points mean roughness Rz as 
prescribed in JIS B0601 was found of the resulting waveform of the 
irregularities. In this manner, the Rz value was obtained of the irregular 
components having the period of not more than 25 .mu.m. 
The surface roughness (Rz) of the cutting edge, which is an angle region, 
of each insert, having sample numbers 53 to 58 in Table 6, was 
approximately 31% (sample numbers 53 and 54), approximately 47% (sample 
number 55), approximately 69% (sample number 56) and approximately 84% 
(sample number 57) and 100% (sample number 38) of the surface roughness Rz 
of the central region. 
It should be noted that modification obvious in the art may be done without 
departing from the scope of the present invention based on the gist 
thereof as herein claimed and disclosed in the entire application. 
TABLES AND DRAWINGS 
Tables 1-6 will follow on the subsequent pages, and the Drawings (FIGS. 1 
to 19) are annexed to the Specification. 
TABLE 1 
__________________________________________________________________________ 
Sintering 
Grain size 
Kind of 
Composition of raw material powders (wt %) 
temp. 
of .beta. phase 
material 
TiC TaC 
Co WC and impurities 
(.degree.C.) 
(.mu.m) 
Remarks 
__________________________________________________________________________ 
A -- -- 5 bal 1400 -- 
B 0.1 -- 5 bal 1400 2 
C 0.5 -- 5 bal 1400 3 
D 3 -- 5 bal 1450 3 
E 3 2 1 bal 1450 3 difficult to sinter 
F 3 2 5 bal 1450 3 
G 3 2 16 bal 1450 3 
H 7 5 7 bal 1450 5 
I 25 -- 10 bal 1450 5 
J 19 17 9 bal 1450 5 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Surface 
Modified surface 
Kind Surface 
crystal 
layer presence 
of Heat treatment conditions 
rough- 
phase 
or not of modified 
Cutting time until peeling 
sample 
mate- 
Atmosphere (%) 
Pressure 
Temper- 
Time 
ness 
by X-ray 
surface layer form- 
Continuous 
Intermittent 
No. rial 
N2 Ar (atm) 
ature (.degree.C.) 
(h) 
Rz (.mu.m) 
analysis 
ed of .beta. (N) phase 
cutting (min) 
cutting 
Remarks 
__________________________________________________________________________ 
*1 F -- -- -- 1 0.9 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NO -- -- Nontreated, 
peeling after 
CVD 
*2 F -- -- 0.00013 
1375 1 1.5 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 In vacuum 
(0.1 Torr) 
*3 F 0 100 1 1375 1 1.7 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
*4 F 0.01 
99.99 
1 1375 1 1.8 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
YES (TRACE) 
&lt;10 &lt;5 
5 F 0.1 99.9 
1.1 1375 1 3.5 .alpha., .beta.&gt;&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
6 F 0.5 99.5 
1 1375 1 5.2 .alpha., .beta.&gt;&gt;&gt;.gamma. 
YES &gt;50 &gt;30 
*7 F 1 99 1 1300 1 1.7 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
8 F 1 99 1 1350 1 3 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
9 F 1 99 1 1375 1 5 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
10 F 1 99 1 1375 3 6.4 .beta.&gt;&gt;.alpha. 
YES &gt;50 &gt;30 
11 F 1 99 1 1375 5 9.1 .beta.&gt;&gt;&gt;.alpha. 
YES &gt;50 &gt;30 
*12 F 1 99 1 1375 10 21 .beta. 
YES &lt;10 &lt;5 Large Sur- 
face rough- 
ness, edge 
chipping 
13 F 1 99 1 1400 1 4.7 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
14 F 1 99 1 1425 1 4.5 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
15 F 1 99 1 1450 1 4.5 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
*16 F 1 99 1 1500 1 4.4 .beta.&gt;.alpha. 
YES &lt;10 &lt;5 Grain growth 
in substrate, 
edge chip- 
ping 
17 F 2 98 1 1375 1 3.5 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
18 F 2 98 1 1375 3 6.5 .beta.&gt;&gt;.alpha. 
YES &gt;50 &gt;30 
19 F 2 98 1 1425 1 4.1 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
20 F 3 97 1 1375 1 3.4 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
*21 F 5 95 1 1330 1 1.6 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
*22 F 5 95 1 1340 1 1.9 .alpha.&gt;.beta.&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
23 F 5 95 0.9 1350 1 3.5 .beta.&gt;.alpha. 
YES &gt;30 &gt;20 
*24 F 5 95 1 1375 1 3.6 .beta., .gamma.&gt;.alpha. 
YES -- -- .gamma. phase 
yielded in 
the surface, 
peeling after 
CVD 
*25 F 10 90 1 1310 1 0.9 .alpha.&gt;&gt;.beta., .gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
*26 F 10 90 1 1320 1 0.9 .alpha.&gt;&gt;.beta., .gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
*27 F 10 90 1 1350 1 3.5 .gamma.&gt;&gt;.beta.&gt;.alpha. 
YES -- -- .gamma. phase 
yielded in 
the surface, 
peeling after 
CVD 
*28 F 100 0 1 1300 1 0.9 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NOT OBSERVED 
&lt;10 &lt;5 
*29 F 100 0 1 1325 1 1.5 TiN, .beta., .gamma. 
NOT OBSERVED 
-- -- .gamma. phase 
yielded in 
the surface, 
peeling after 
CVD 
*30 F 100 0 1 1350 1 3.4 .gamma.&gt;.beta. 
YES -- -- .gamma. phase 
yielded in 
the surface, 
peeling after 
CVD 
__________________________________________________________________________ 
No mark: Inventive example 
*: Comparative example 
1 ATM = 0.101 MPa 
TABLE 3 
__________________________________________________________________________ 
Surface 
Modified surface 
Kind Surface 
crystal 
layer presence 
of Heat treatment conditions 
rough- 
phase 
or not of modified 
Cutting time until peeling 
sample 
mate- 
Atmosphere (%) 
Pressure 
Temper- 
Time 
ness 
by X-ray 
surface layer form- 
Continuous 
Intermittent 
No. rial 
N2 Ar (atm) 
ature (.degree.C.) 
(h) 
Rz (.mu.m) 
analysis 
ed of .beta. (N) phase 
cutting (min) 
cutting 
Remarks 
__________________________________________________________________________ 
*31 F 0 100 30 1320 1 26 .beta.&gt;&gt;&gt;.alpha., .gamma. 
YES &lt;10 &lt;5 Sintered in 
BN case 
*32 F 0.004 
99.996 
1000 
1350 1 21 .beta.&gt;&gt;&gt;.alpha., .gamma. 
YES &lt;10 &lt;5 
*33 A 2 98 1 1375 3 1.3 .alpha.&gt;&gt;&gt;.gamma. 
NO &lt;10 &lt;5 No .beta. phase 
*34 B 2 98 1 1375 3 1.5 .alpha.&gt;&gt;&gt;.beta.&gt;.gamma. 
YES (trace) 
&lt;10 &lt;5 Insufficient 
.beta. phase 
35 C 2 98 0.8 1375 3 5.2 .alpha.&gt;&gt;.beta.&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
36 D 2 98 1 1375 3 6.3 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
YES &gt;50 &gt;30 
*37 G 2 98 1 1375 3 6.6 .alpha.&gt;.beta.&gt;.gamma. 
YES &lt;10 &lt;5 Large 
amount of 
.gamma. 
phase 
38 H 2 98 1.2 1375 3 7.1 .alpha., .beta.&gt;&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
*39 I 2 98 1 1375 3 13.5 
.beta. 
YES (HARD TO 
&lt;10 &lt;5 Large 
DISTINGUISH amount of 
.beta. 
FROM THE phase, edge 
INTERIOR) chipping 
*40 J 2 98 1 1375 3 16.8 
.beta. 
YES (HARD TO 
&lt;10 &lt;5 Large 
DISTINGUISH amount of 
.beta. 
FROM THE phase, edge 
INTERIOR) chipping 
__________________________________________________________________________ 
No mark: Inventive example 
*: Comparative example 
1 ATM = 0.101 MPa 
TABLE 4 
__________________________________________________________________________ 
Sintering 
Grain size 
Kind of 
Composition of raw material powders (wt %) 
temp. 
of .beta. phase 
material 
TiC TaC 
Co WC and impurities 
(.degree.C.) 
(.mu.m) 
Remarks 
__________________________________________________________________________ 
a 0.5 -- 5 bal 1400 3 C of Table 1 
b 3 -- 5 bal 1450 3 D of Table 1 
c 3 2 5 bal 1450 3 F of Table 1 
d 7 5 7 bal 1450 5 H of Table 1 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Cutting time 
Modified 
until peeling 
Surface Surface 
surface layer 
Con- 
Inter- 
Heat treatment conditions 
roughness Rz 
Image analysis 
crystal 
presence or 
tinuous 
mittent 
Pres- 
Temper- Con- 
Non- Ampli- 
phase 
of modified 
cutting 
cutting 
Sample 
Kind of 
Atomosphere (%) 
sure 
ature 
Time 
tactor 
contact 
Engage 
tude 
by X-ray 
face layer 
test- 
test 
No. material 
N2 Ar (atm) 
(.degree.C.) 
(h) 
(.mu.m) 
(.mu.m) 
ratio 
(.mu.m) 
analysis 
ed of .beta. (N) 
(min) 
(min) 
__________________________________________________________________________ 
*41 c -- -- -- -- -- 0.9 
0.5 1.1 0.5 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
NO -- -- 
42 c 0.1 99.9 
1.1 
1375 1 3.5 
3 1.2 3 .alpha., .beta.&gt;&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
*43 c 1 99 1 1330 1 2.3 
1.5 1.1 1.5 .beta.&gt;.alpha. 
YES &lt;20 &lt;10 
44 c 1 99 1 1375 1 5 4.9 1.4 5 .beta.&gt;.alpha. 
YES &gt;50 &gt;30 
45 c 1 99 1 1375 3 6.4 
4.9 1.5 6 .beta.&gt;&gt;.alpha. 
YES &gt;60 &gt;40 
46 c 1 99 1 1375 5 9.1 
4.8 1.6 12 .beta.&gt;&gt;&gt;.alpha. 
YES &gt;60 &gt;40 
*47 c 1 99 1 1375 10 21 12 2 25 .beta. 
YES &lt;10 &lt;5 
*48 c 0 100 30 1320 1 26 15 2.6 30 .beta.&gt;&gt;&gt;.alpha., 
YESmma. &lt;10 &lt;5 
49 a 2 98 0.8 
1375 3 5.2 
3.7 1.3 4 .alpha.&gt;&gt;.beta.&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
50 b 2 98 1 1375 3 6.3 
4.5 1.4 5 .alpha.&gt;.beta.&gt;&gt;&gt;.gamma. 
YES &gt;50 &gt;30 
51 d 2 98 1.2 
1375 3 7.1 
5.3 1.5 3 .alpha., .beta.&gt;&gt;&gt;.gamma. 
YES &gt;30 &gt;20 
*52 c 0.01 
99.99 
10 1350 3 8.2 
2.8 1.2 2 .beta.&gt;&gt;.alpha. 
YES &lt;20 &lt;10 
__________________________________________________________________________ 
No mark: Inventive example 
*: Comparative example 
1 ATM = 0.101 MPa 
TABLE 6 
__________________________________________________________________________ 
Thickness of modified 
Surface Cutting time until peeling 
surface layer 
irregularity 
Continuous 
Intermittent 
Surface 
Sample 
Honing 
Edge Center 
Edge 
Center 
cutting test 
cutting test 
state 
No. (R:.mu.m) 
(.mu.m) 
(.mu.m) 
(.mu.m) 
(.mu.m) 
(min) (min) of work 
__________________________________________________________________________ 
*53 0 2.5 8 1.5 4.9 &gt;50 &gt;30 good 
*54 0.002 
3 8 1.5 4.9 &gt;50 &gt;30 good 
55 0.008 
4.5 8 2.3 4.9 &gt;60 &gt;40 good 
56 0.03 
6 8 3.4 4.9 &gt;120 &gt;70 good 
57 0.08 
7.2 8 4.1 4.9 &gt;110 &gt;65 slightly good 
58 0.12 
8 8 4.9 4.9 &gt;105 &gt;60 bad 
__________________________________________________________________________ 
No mark: Inventive example 
*: Comparative example