JPH0421568A - Fine crystalline sintered compact with high hardness and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title sintered compact with improved wear resistance by bringing a metal (alloy) containing a specified amount of another metal in the iron group into contact with a resin-derived noncrystalline carbon incorporated with each specified size of diamond powder and high-pressure phase-type boron nitride powder etc., followed by sintering under pressure at specified conditions. CONSTITUTION:Firstly, a resin-derived noncrystalline carbon is incorporated with (A) diamond powder 1-3mum in size and (B) high-pressure phase-type boron nitride powder <=3mum (in size and/or (C) diamond powder <=1mum in size. Thence, the resulting noncrystalline carbon is brought into contact with a metal (alloy) containing >=5wt.% of another metal in the iron group to effect manifestation of catalytic activity. The resulting noncrystalline carbon is then sintered at >=1250 deg.C under a pressure corresponding to the diamond-stable region in terms of thermodynamics.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-hardness microcrystalline sintered body useful as a wear-resistant part such as the cutting edge of a cutting tool, a dresser, a die, etc., and a method for manufacturing the same. be.

[Prior Art] Diamond sintered bodies have high hardness and excellent wear resistance, and have thus far been used as materials for cutting tool edges, wire drawing dies, and the like. However, compared to natural diamond meteorite tools, the finished surface accuracy of the workpiece is poor, and it has the disadvantage that it is impossible to obtain a surface that is so precise that it can be called a mirror surface. In other words, the particle size of the constituent diamond particles in a commercially available diamond sintered body is approximately 3 to 20 μm, and the cutting tool edge using this sintered body has irregularities that roughly correspond to the size of the crystal grains. It is thought that the main reason for this is that the cutting edge is not as sharp as that of diamond single stone masonry (see Japanese Patent Publication No. 58-32224).

In order to avoid the above-mentioned disadvantages, it is conceivable to make the diamond crystal grains constituting the sintered body extremely fine, with a diameter of 3 μm or less. However, it is not possible to produce a sintered body with a desired fine grain structure using the high temperature and high pressure method that has been commonly practiced. That is, as confirmed by the inventors through experiments,
Fine particles of 3 μm or less are used as raw material diamond powder, and when these are sandwiched between Co plates and sintered in an ultra-high pressure and high temperature generator at 60 kilobar and 1450°C, some of the diamond fine particles are about 50 to 500 μm in size. The particles grew into coarse particles, making it impossible to obtain a sintered body with the desired fine grain structure. On the other hand, when diamond powder having a diameter of 3 μm or more was used as the raw material diamond powder, grain growth did not occur during the sintering process, and a sintered body with a uniform structure could be obtained. This is considered to be the reason why the optimum particle size of the raw material diamond particles constituting commercially available diamond sintered bodies is about 3 μm.

On the other hand, a technique capable of suppressing grain growth during sintering even when diamond powder of 3 μm or less is used as a raw material has been developed, for example, as seen in the above-mentioned Japanese Patent Publication No. 58-32224. . This technology works with diamond particles of less than 1 μm as well as diamond particles of less than 1 μm.
a.5a.

The purpose is to use group 6a metal carbides, nitrides, borides, mixtures thereof, or mutual solid solution compounds as raw materials, and to suppress the growth of fine diamond particles using these materials.

However, when the present inventors actually produced and examined a prototype sintered body according to the above-mentioned technical content, it was found that the addition of the above compound certainly had the effect of suppressing the grain growth of diamond particles, but the hardness of the sintered body was was found to be significantly lower than that of diamond sintered bodies. This is thought to be because the hardness of the above-mentioned compound used in combination is much smaller than that of diamond. Moreover, since the above-mentioned technique uses a powdered raw material, there is a problem in that gas is easily adsorbed on the surface of the raw material powder, which inhibits sintering and leaves an unsintered portion.

Therefore, the inventors of the present invention solved the problem without reducing the hardness of the sintered body.
As a method that can also suppress the grain growth of fine diamonds during sintering, we developed a method in which fine diamonds are mixed with fine high-pressure phase boron nitride of 1 μm or less and sintered. proposed as.

However, when further research was carried out that night, it was discovered that the sintered body of the prior invention, which uses fine diamond as a raw material, has a diameter of 3 μm.
It has become clear that the wear resistance is insufficient compared to a sintered body obtained using coarse-grained diamond, and that there is still room for improvement in this respect.

[Problems to be Solved by the Invention] The present invention has been made to solve the problems of the prior art, and its purpose is to solve the problems of the prior art. The object of the present invention is to provide a high-hardness, microcrystalline sintered body that has excellent finished surface accuracy and excellent wear resistance, and a method for manufacturing the same.

[Means for solving the problem] The high hardness microcrystalline sintered body according to the present invention is
Diamond with a diameter of 3 μm or less: 30 to 93% by volume, high-pressure phase boron nitride with a diameter of 3 μm or less: 2 to 20% by volume, the balance being a metal catalyst for diamond synthesis (containing 5% by weight or more of iron group metals) or a metal catalyst with a diameter of 1 μm or less The key point is that the diamonds are directly connected to each other and form an interlocking phase.

Furthermore, the method for producing a high hardness microcrystalline sintered body according to the present invention is as follows:
Resin-derived amorphous carbon containing diamond powder and high-pressure phase type boron nitride powder in the above ratio is brought into contact with a metal or alloy containing 5% by weight or more of iron group metal, and at a temperature of 1250°C or higher and thermodynamically The key point is that pressure sintering is performed at a pressure in the diamond stable region.

[Function] As clarified in the above-mentioned publication, when high-phase boron nitride, which has a hardness second only to diamond, is dispersed in diamond powder with a particle size of 1 μm or less and sintered at high temperature and high pressure, it becomes diamond. A highly hard microcrystalline sintered body can be obtained while suppressing grain growth during sintering.

However, a sintered body using such fine diamond powder has poor wear resistance as described above, and has a surprisingly short lifespan when used as a cutting edge material for a tool. However, when diamond powder with a diameter of more than 1 μm and less than 3 μm is used,
It was confirmed that the sintered body has high hardness and excellent wear resistance, and can significantly extend the life when used as a cutting edge material.

In addition, in the conventional technology, as mentioned above, powdered raw materials were sintered, which caused problems such as gas adsorption, but in the present invention, a resin-based material containing diamond powder and high-pressure phase type boron nitride powder was used. By using amorphous carbon as a raw material, the above-mentioned disadvantages can also be overcome.

That is, since the resin-derived amorphous carbon can be produced from liquid powder as will be explained in detail later, the high-pressure phase type boron nitride powder and the diamond powder can be well dispersed in each other.
It becomes possible to obtain a desired high hardness fine crystal sintered body without causing the disadvantages such as gas adsorption described in the prior art.

Resin-derived amorphous carbon is also called glassy carbon, and a typical example is furan resin-derived amorphous carbon, which is produced by adding an acid catalyst to furfuryl alcohol and subjecting it to dehydration condensation. This is a resin that has been carbonized. Therefore, in the case of using furan resin-derived amorphous carbon as the resin-derived amorphous carbon in the present invention, a predetermined amount of the raw material powder is mixed and dispersed in furfuryl alcohol and then subjected to the above treatment. A solid amorphous carbon derived from furan resin is obtained. After degassing the resin-derived amorphous carbon containing raw material powder obtained in this way under high-temperature vacuum, metal catalysts are arranged in layers or concentrically and brought into contact with each other, and sintered at high temperature and high pressure. The originating amorphous carbon itself is converted into diamond, and the whole becomes a highly hard sintered body with diamond as a directly bonded phase.

The resin-derived amorphous carbon that contains the raw material powder dispersedly is a dense solid substance, and after degassing, there is almost no adsorption of gas components, and the raw material powder is evenly coated with carphone. Become something.

In the above, furan resin-derived amorphous carbon obtained by carbonizing furan resin was shown as a representative example of resin-derived amorphous carbon, but the resin-derived amorphous carbon used in the present invention is limited to that derived from furan resin. However, even if it is derived from other thermosetting resins such as phenol formaldehyde resin, acetone/furfural copolymer resin, furfuryl alcohol/phenol copolymer resin, urea resin, melamine resin, xylene resin, toluene resin, guanamine resin, etc. Can be used similarly.

In order to obtain the desired composite sintered body, the sintering temperature must be 1250° C. or higher; if it is less than 1250° C., the sinterability is poor. Moreover, the pressure during sintering must naturally be within the thermodynamic diamond stability region, and a pressure of about 40 kilobar or more is required. Further, as the metal catalyst used in the sintering step, iron group metals such as iron, cobalt, and nickel are used, and an alloy containing 5% by weight or more of any of the iron group metals exhibits a sufficient catalytic effect. However, if the amount of iron group metal is less than 5% by weight, the catalytic action will not be effectively exhibited and the sinterability will deteriorate.

However, in the present invention, the diamond powder has a diameter of more than 1 μm.
The major feature is that ultrafine powder of less than 1 μm is selected and used, and although it is possible to obtain a sintered body that provides cutting tools with high finishing accuracy, it has poor wear resistance. On the other hand, if coarse grains exceeding 3 μm are used, the sintered body will have minute irregularities, making it unsuitable for use in cutting tools with high finishing accuracy.

However, if the diameter is more than 1 μm but not more than 3 μm, it is possible to obtain a sintered body that satisfies both wear resistance and surface precision.

Note that the high-pressure phase type boron nitride in the present invention includes two types, cubic type boron nitride and wurtzite type boron nitride, and therefore, in the present invention, either one may be used alone. It is also possible to use multiple images. However, since wurtzite-type boron nitride powder generally has a particle size of 3 μm or less, it can be used as is, but cubic-type boron nitride powder ranges from coarse to fine particles of 1 μm or less, so the present invention When using cubic boron nitride, it is necessary to select one with a particle size of 3 μm or less, or to use it after classification. In addition, when comparing the same amount of addition,
Since the smaller the grain size of the high-pressure phase type boron nitride, the greater the effect of suppressing diamond grain growth, it is desirable to use a grain size of 1 μm or less.

In the sintered body according to the present invention, the content of fine diamonds exceeding 1 μm and 3 μm or less needs to be 30 to 93% by volume. In other words, when the diamond content exceeds 93% by volume, the high-pressure phase type boron nitride becomes relatively insufficient, and the effect of suppressing diamond grain growth during sintering is not sufficiently exhibited.On the other hand, when the diamond content is less than 30%, , the target level of wear resistance cannot be achieved. In addition, the content of high pressure phase type boron nitride is
It is necessary to set it as 2-20 volume%. This is because if the content of high-pressure phase type boron nitride exceeds 20% by volume, wear resistance will be insufficient, and if it is less than 2% by volume, the effect of suppressing diamond grain growth during sintering will not be effectively exhibited. . In addition, in the present invention, as another component, 1 μm
It is also possible to further improve the sinterability of the sintered body by blending a small amount of the following fine diamond powder. However, if the amount is too large, the wear resistance will be insufficient, so it is preferable to limit the amount to about 50% by volume or less.

Furthermore, as mentioned above, in the sintered body of the present invention, a metal or alloy containing 5% or more of iron group metal is used as a metal catalyst in the manufacturing stage, so the obtained sintered body naturally contains the metal catalyst. Become.

Hereinafter, the present invention will be explained in more detail with reference to examples, but the following examples are not intended to limit the present invention.
It is within the technical scope of the present invention that any suitable changes and implementations may be made within the scope of the spirit described below.

[Example] Furfuril was added to a mixed powder in which diamond powder with a particle size of 1 μm or less and more than 1 μm and less than 3 μm and cubic boron nitride powder (CBN) with a particle size of less than 1 μm and more than 1 μm and less than 3 μm were thoroughly mixed in various ratios. Alcohol was added and further mixed, and after adding a small amount of nitric acid, the mixture was heated to 70°C for dehydration condensation to convert furfuryl alcohol into a resin. This is 80
Carbonization was performed at 0 t to obtain dense solid furan resin-derived amorphous carbon containing raw material powder.

The obtained amorphous carbon derived from furan resin was processed into a disk shape with a diameter of 1° and a thickness of 1 mm, and heated to 1 x 10-'Torr.

Degassing treatment was performed at 1450°C. These were sandwiched between 10% CO-containing cemented carbide plates and cobalt plates with catalytic action, and sintered at 60 kilobar and 1480°C using an ultra-high pressure and high temperature generator.
7 and No. 1' to 5° were obtained.

For each of the obtained sintered bodies, we investigated the composition ratio of the four constituents, the structure of the sintered body, and the wear resistance by cutting tests.
The results shown in Table 1 below were obtained.

In the cutting test, each sintered body was cut to create a cutting chip, and a round bar of A112% Si alloy with a diameter of 80 mm was cut at a cutting speed of 300 m/min and a feed of 0.02 m +.
The cutting was carried out under the conditions of n/rotation and a cutting depth of 0.05 mm. However, cutting tests were not conducted for sintered bodies No. 2' and 4° because the grains were coarse.

As a result, there was almost no difference in the roughness of the machined surface of the work material compared to that obtained by cutting under the same conditions using a natural diamond stone tool, and a nearly mirror-like finished surface was obtained.

Wear resistance also refers to the time it takes to reach the end of each chip's lifespan.
No. 1' was evaluated as 1, and the results shown in Table 1 were obtained.

From Table 1, it can be considered as follows.

(1) Examples 1 to 7 are examples that satisfy the present invention, in which a homogeneous microstructure was obtained, a good finished surface was obtained in the cutting test, and the wear resistance was lower than that of the comparative example 1°. 2
It can be seen that it is more than twice as good as the cutting member.

(2) Reference numerals 1' to 5' are comparative examples lacking any of the requirements defined by the present invention as shown below, and the abrasion resistance of all of them is below that of the present invention.

Code 1°: Diamonds with a diameter of more than 1 μm and less than 3 μm are not blended.

Code 2″, 4°: The amount of high-pressure phase type boron nitride is less than the specified range, so the sintered body is partially grained.

Code 3゛: The amount of diamonds larger than 1 μm and 3 μm or less is less than the specified range, and no significant improvement in wear resistance is observed.

Code 5°: The amount of high-pressure phase type boron nitride exceeds the specified range and the wear resistance is poor.

[Effects of the Invention] As described above, according to the present invention, by employing the above-mentioned configuration, fine particles suitable for high-hardness machining tools, etc. that have good wear resistance and excellent finished surface accuracy can be produced. It is now possible to provide a crystal sintered body.

Claims (2)

[Claims] (1) Diamond over 1 μm and 3 μm or less: 30-93
High-pressure phase boron nitride of 3 μm or less in volume%: 2 to 20 volume%, the balance consisting of a metal catalyst for diamond synthesis (containing 5% by weight or more of iron group metals) or this and diamond of 1 μm or less, which is structurally similar to diamond A high hardness microcrystalline sintered body characterized by forming a directly connected phase. (2) Diamond powder of more than 1 μm and less than 3 μm and 3 μm
The resin-derived amorphous carbon containing the following high-pressure phase type boron nitride powder or this and diamond powder of 1 μm or less,
Contacting a metal or alloy containing 5% by weight or more of an iron group metal,
A method for producing a high-hardness microcrystalline sintered body, which comprises pressure sintering at a temperature of 1250° C. or higher and a pressure in the thermodynamic diamond stability region.