JPH05132704A - High-hardness microcrystal sintered compact and production thereof - Google Patents

Abstract

PURPOSE:To produce the high-hardness microcrystal sintered compact capable of attaining an excellent finished-surface roughness when used for the edge of a cutting tool, a drawing die, etc., and excellent in wear resistance. CONSTITUTION:This sintered compact contains 60-94vol.% of diamond having <=3mum grain diameter, 1-40vol.% of high-pressure phase-type boron nitride having <=3mum grain diameter and the balance diamond synthesizing metallic catalyst (contg. >=5wt.% of iron-family metal), and a solid soln. is formed at the grain boundary between the diamond and boron nitride as the structure. Meanwhile, such a sintered compact is also obtained by bringing a metal or alloy contg. >=5wt.% iron-group metal into contact with the amorphous carbon formed from the resin contg. the diamond powder having <=3mum grain diameter and the high-pressure phase-type boron nitride powder having <=3mum grain diameter and pressure-sintering the mixture at >=1350 deg.C and at a pressure in the thermodynamic diamond stabilizing region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high hardness fine crystal sintered body useful as a wear resistant part such as a cutting edge of a cutting tool, a dresser and a die, and a method for producing the same.

[0002]

2. Description of the Related Art Since a diamond sintered body has a high hardness and abundant wear resistance, it has been conventionally used as a material for a cutting edge of a cutting tool or a wire drawing die. Roughness of the finished surface of the workpiece is rough compared to
It has a drawback that it is not possible to obtain a dense surface that can be called a mirror surface. That is, in the commercially available diamond sintered body, the grain diameter of the constituent diamond is about 3 to 20 μm,
The main reason is that the cutting edge of the cutting tool using this sintered body has irregularities corresponding to the size of crystal grains, and it cannot be a sharp cutting edge like a natural diamond monolithic tool. It is considered (for example, Japanese Patent Publication No. 58-3222)
No. 4).

In order to avoid the above-mentioned inconvenience, it is easily conceivable that the diamond crystal grains constituting the sintered body should be extremely fine with a size of 3 μm or less. However, it has been impossible to produce a desired sintered body even if the conventional general high temperature and high pressure method is adopted. That is, the inventors of the present invention have confirmed by experiments that fine diamond particles of 3 μm or less are used as the raw material diamond powder, and Co
Even if the plates are stacked and sintered by the ultrahigh pressure and high temperature generator under the conditions of 60 kbar and 1450 ° C., some of the diamond fine particles only grow to coarse particles having a size of about 50 to 500 μm. However, the desired sintered body could not be obtained. On the other hand, when a raw material diamond powder having a particle size of 3 μm or more was used, no grain growth was observed and a sintered body could be obtained. This seems to be the reason why the finest constituent diamond particles of the commercially available diamond sintered body are about 3 μm.

By the way, even if diamond powder having a particle diameter of 3 μm is used as a raw material, a technique for suppressing grain growth during sintering is disclosed in, for example, the above-mentioned Japanese Patent Publication No.
For the time being, it has been developed as seen in Japanese Patent No. 32224. In this technique, in addition to diamond particles having a particle size of 1 μm or less, carbides, nitrides, borides of a metal of group 4a, 5a, 6a of the periodic table having a particle size of 1 μm or less, or a mixture thereof or a mutual solid solution compound is used as a raw material. It is intended to suppress the grain growth of fine diamond grains by mixing them.

However, the inventors of the present invention actually manufactured and examined a sintered body in accordance with the above technical contents, and although the effect of suppressing the grain growth of diamond particles by the addition of the above compound was confirmed, the sintered body It was found that the hardness shows a significant decrease as compared with the usual diamond sintered body. It is considered that this is because the hardness of the above compound is much smaller than that of diamond. Moreover, since the above-mentioned technique uses a powdery raw material, there is a problem that gas is easily adsorbed on the surface of the raw material powder, so that sintering is hindered and an unsintered portion remains.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art, and its purpose is to use it for the cutting edge of a cutting tool or a wire drawing die. It is an object of the present invention to provide a fine crystal sintered body having excellent finished surface roughness, high hardness and excellent wear resistance, and a method for producing the sintered body.

[0007]

The high hardness fine crystal sintered body according to the present invention is a diamond having a grain size of 3 μm or less: 60 to
94% by volume, high-pressure phase type boron nitride having a particle size of 3 μm or less: 1 to
40% by volume, the balance consisting of a metal catalyst for synthesizing diamond (however, containing 5% by weight or more of an iron group metal), has a gist in that a solid solution is formed at the grain interface between diamond and high-pressure phase boron nitride due to its structure. It is a thing.

The high hardness fine crystal sintered body as described above is a resin-derived amorphous carbon containing diamond powder having a grain size of 3 μm or less and high-pressure phase boron nitride powder having a grain size of 3 μm or less,
Contacting a metal or alloy containing 5% by weight or more of an iron group metal,
It is obtained by pressure sintering at a temperature of 1350 ° C. or higher and at a pressure in the thermodynamic stable region of the tire Mondo.

[0009]

The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, disperse a high-pressure phase type boron nitride having a hardness second to that of diamond in diamond powder at high temperature.
By sintering under high pressure, grain growth during sintering in diamond can be suppressed, and a solid solution can be formed at the grain interface between diamond and high-pressure phase boron nitride, and a high-hardness microcrystalline sintered body can be realized. The present invention has been completed here.

On the other hand, in the sintered body as shown in the prior art, carbides, nitrides, borides of the metals of groups 4a, 5a and 6a of the Periodic Table, their mixtures or mutual solid solutions,
It was considered that diamond could not form a solid solution at the grain interface, which was the cause of the weak bonding force between grains. Further, as described above, in the prior art, the powdery raw material was sintered, so that inconveniences such as gas adsorption occurred, but the present inventors also considered this point, and the diamond powder and the high-pressure phase were taken into consideration. By using a resin-derived amorphous carbon containing a type boron nitride powder as a raw material, the above-mentioned inconvenience can be solved. That is, since the resin-derived amorphous carbon can be produced from a liquid monomer as described in detail later, it is possible to appropriately disperse the high-pressure phase boron nitride powder and the diamond powder,
The desired high-hardness fine crystal sintered body could be realized without causing the inconvenience such as gas adsorption described in the prior art.

The resin-derived amorphous carbon is the same material as what is called glassy carbon, and a typical example thereof is furan resin-derived amorphous carbon, which uses furfuryl alcohol with an acid catalyst. The furan resin obtained by addition and dehydration condensation is carbonized. Therefore, when furan resin-derived amorphous carbon is used as the resin-derived amorphous carbon in the present invention, a predetermined amount of the raw material powder is obtained by mixing and dispersing the raw material powder in furfuryl alcohol and then performing the above treatment. An amorphous carbon derived from the solid furan resin contained is obtained. The raw material powder-containing resin-derived amorphous carbon thus obtained is subjected to degassing treatment under high temperature vacuum (this is a problem in the prior art), and then the metal catalysts are laminated or concentrically arranged and brought into contact with each other. By sintering under high pressure, the resin-derived amorphous carbon itself is converted into diamond, and at the same time, a high-hardness sintered body having diamond as a binder phase is obtained as a whole.

The resin-derived amorphous carbon in which the raw material powder is dispersed and contained is a dense solid substance, and once the degassing treatment is performed, the adsorption of gas components is small, and a molded body in which the raw material powder is uniformly coated with carbon is obtained. Form.

In the above invention, a furan resin-derived amorphous carbon obtained by carbonizing a furan resin is shown as a typical example of the resin-derived amorphous carbon. However, the resin-derived amorphous carbon used in the present invention is derived from the furan resin. Not limited to those, other phenol formaldehyde resin, acetone-furfural copolymer resin, furfuryl alcohol-phenol copolymer resin,
A thermosetting resin derived from a urea resin, a melamine resin, a xylene resin, a toluene resin, a guanamine resin or the like can be treated in the same manner, and the type of the resin is not limited.

The sintering temperature for obtaining the desired composite sintered body must be 1350 ° C. or higher, and if it is lower than 1350 ° C., the sinterability is poor. As a matter of course, the pressure at the time of sintering needs to be a thermodynamic diamond stable region pressure, and a pressure of about 40 kbar or more is required. Further, the metal catalyst used in the sintering step needs to be an iron group metal such as iron, cobalt, nickel, etc., and an alloy containing 5% by weight or more of any of the iron group metals provides sufficient catalytic action. To be demonstrated. However, when the iron group metal is less than 5% by weight, the catalytic action is not exhibited and the sinterability is deteriorated.

In the present invention, however, it is necessary to select and use diamond powder having a particle size of 3 μm or less,
If coarse particles having a particle size of more than 3 μm are used, fine irregularities will be generated in the sintered body, which lacks suitability as a cutting tool that requires high finishing accuracy. By using diamond having the above grain size, a sintered body satisfying both wear resistance and surface accuracy can be obtained.

On the other hand, the high-pressure phase type boron nitride in the present invention is meant to include two types of cubic boron nitride and wurtzite type boron nitride, and therefore either one is used alone in the present invention. It is also possible that both are mixed and used. However, since wurtzite type boron nitride powder generally has a particle size of 1 μm or less, it can be used as it is, but cubic type boron nitride powder can be used in the present invention since it ranges from coarse particles to fine particles of 1 μm or less. When using cubic boron nitride, it is necessary to select and use one having a particle size of 3 μm or less (preferably 1 μm or less).

In the sintered body according to the present invention, the grain size is 3 μm.
The content of fine diamond of m or less is 60 to 94% by volume.
And need to. That is, if the content of diamond exceeds 94% by volume, the high-pressure phase boron nitride is relatively insufficient, the effect of suppressing the growth of diamond grains is not exhibited, and the grain growth of diamond occurs during sintering, which is not preferable. If it is less than 60% by volume, the sinterability of diamond is lowered and the wear resistance is lowered. The content of high-pressure phase boron nitride is 1 to 40.
It is necessary to set the volume% (preferably 3 to 7% by volume).
This is because if the content of the high-pressure phase type boron nitride exceeds 40% by volume, the wear resistance is poor, and if it is less than 1% by volume, the effect of suppressing the grain growth of diamond during sintering is small.

As described above, the sintered body according to the present invention uses a metal or an alloy containing 5% or more of an iron group metal as a metal catalyst in the manufacturing stage thereof, and thus the obtained sintered body is the metal catalyst. Will naturally include.

The present invention will be described in more detail with reference to the following examples, but the following examples are not intended to limit the present invention, and any design changes made to the gist of the preceding or the following will not affect the present invention. It is included in the technical scope.

[0020]

[Examples] Furfuryl alcohol was added to a mixed powder obtained by sufficiently mixing diamond powder having a particle size of 3 μm or less and cubic boron nitride powder (cBN) having a particle size of 3 μm or less at various ratios, and further mixed to obtain a trace amount. After adding the nitric acid in Example 1, the mixture was heated to 70 ° C. for dehydration condensation to make furfuryl alcohol into a resin. This was carbonized at 800 ° C. to obtain dense solid furan resin-derived amorphous carbon containing raw material powder.

The furan resin amorphous carbon thus obtained was treated with a diameter of 10
mm, thickness 1mm, processed into a disk shape, 1 × 10 ^-5 Torr, 145
The degassing treatment was performed under the condition of 0 ° C. These were sandwiched between a 10% Co-containing cemented carbide plate having a catalytic action and an iron-group metal plate, and 65 kilobars, 1
Sintering was performed under the condition of 550 ° C., and various sintered body samples (N
o.1-5) was obtained.

With respect to each of the obtained sintered bodies, the composition ratio of each constituent, the sintered body structure and the wear resistance were investigated. At this time, as comparative examples, those not containing cBN (No. 6), cB
High N content (No.7), W instead of cBN
The same investigation was conducted on the sintered bodies obtained by similarly sintering the ones containing C or TiC (No. 8, 9).

The wear resistance is obtained by cutting each sintered body to prepare a cutting tip, and using a round bar Al-1 having a diameter of 80 mm as a work material.
Cutting speed 400m / min, feed rate of 6% Si alloy
A cutting test was performed under the conditions of 1 mm / rotation and depth of cut 0.1 mm.
The life was reached when the bald surface wear reached 0.2 mm, and the relative life was shown when the life of the sintered body of Comparative Example No. 7 was set to 1. The results are collectively shown in Table 1, and it can be seen that the examples show better wear resistance than the comparative examples.

[0024]

[Table 1]

Next, with respect to the sample No. 3, an X-ray diffraction pattern of the raw material powder and the sintered body was investigated, and the results shown in FIG. 1 were obtained. 1 (a) shows the X-ray diffraction pattern of the raw material powder, and FIG. 1 (b) shows the X-ray of the sintered body.
A line diffraction pattern is shown. From FIG. 1, the following can be considered. That is, in the sintered body, the cBN peak was smaller than that of the raw material powder, and the strength of the intermediate portion between the diamond and cBN peaks was somewhat higher, forming a solid solution at the grain interface between diamond and cubic boron nitride. I thought it was.

[0026]

As described above, according to the present invention, by adopting the above-mentioned constitution, it is possible to obtain a fine crystal sintered body which has an excellent finished surface roughness and is also excellent in wear resistance. did it.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction pattern of a raw material powder of Sample No. 3 and a sintered body.

Claims (2)

[Claims] 1. A diamond having a particle size of 3 μm or less: 60 to
94% by volume, high-pressure phase type boron nitride having a particle size of 3 μm or less: 1 to
40% by volume, the balance consisting of a metal catalyst for synthesizing diamond (however, containing 5% by weight or more of an iron group metal), is characterized in that a solid solution is formed at the grain interface of diamond and high-pressure phase type boron nitride on the texture. High hardness fine crystal sintered body. 2. A metal or alloy containing 5 wt% or more of an iron group metal is brought into contact with resin-derived amorphous carbon containing diamond powder having a particle size of 3 μm or less and high-pressure phase boron nitride powder having a particle size of 3 μm or less. The sintered compact according to claim 1 is produced by pressure sintering at a temperature of 1350 ° C. or higher and a pressure in a thermodynamic diamond stable region. Manufacturing method.