JPS5823343B2 - Manufacturing method of diamond sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a high strength and tough diamond sintered body using synthetic or natural diamond fine particles as a main raw material.

Diamond sintered bodies are used as cutting tools and wire drawing dies.

Diamond is a typical covalently bonded material and is a high melting point material, making it extremely difficult to sinter.

When fine diamond particles are preformed and kept at a high temperature and high pressure region where diamond is stable, for example, 70Kb and 1600℃ for several minutes, it takes on the appearance of a sintered body, but its compressive strength and hardness are lower than that of single crystal diamond. It is extremely low.

When we investigated the cause, we found that although it cannot be said that there is no intergranular bonding between diamonds, a larger amount of graphite than expected, for example about 20% by volume, was precipitated, and this graphite acts as a binding agent for diamonds. It can be seen that this leads to deterioration of properties.

The reason why graphite is precipitated in this way is considered to be that part of the diamond is graphitized, and the surface of the diamond particles is exposed to voids, resulting in deterioration of properties.

As a way to solve this problem, by mixing diamond particles with fine powders of iron, nickel, cobalt, etc. that can dissolve diamond, and sintering this as a raw material, a sintered body in which diamond particles are bonded with metal is created. Obtainable.

However, this sintered body has a micro Vickers hardness of 30
00 Ky/vrm", which is about 10
, 000 Kp/mm'' or more.

Moreover, such two-phase sintered bodies also have significantly inferior wear resistance.
Its use as a cutting tool is extremely limited.

However, by using a mixture of fine diamond particles and cobalt and under appropriate conditions, it is possible to produce a sintered body in which cobalt is leached from the mixed powder system and diamond particles are directly bonded to each other.

This sintered body has a micro Vickers hardness of 7000 to 80.
00 Kp, 4'', wear resistance is also obtained for use as a cutting tool.

In such a sintered body in which diamond particles are directly bonded to each other, it is necessary that graphite or non-diamond carbon exists in advance on the surface of the diamond or in the bonded portion.

It is believed that such graphite or non-diamond carbon dissolves in the cobalt liquid phase and, during the sintering process, cobalt is leached out and at the same time binds the diamond particles.

The same thing can be said when iron nickel is used instead of cobalt.

However, the sintered body produced in this manner has the drawback that the diamond particles sometimes grow to several tens to 100 μm.

Such grain-grown diamond sintered bodies tend to have particles that fall off during cutting when used as tools, and there are some problems in wear resistance and toughness.

The present invention solves this problem and provides a method for manufacturing a diamond sintered body consisting only of fine particles of several μm or less.

The present invention has been made as a result of research to achieve the above object.
0.2- at the same time as metal powders such as nickel and iron.

The problem was solved by mixing and sintering 3% by weight of metallic boron powder.

That is, the present invention uses synthetic or natural diamond fine particles, preferably those with an average particle size of 2 μm or less, as the main raw material,
Cobalt of 2 to 20 weight percent to this.

One or more of the metals nickel or iron or their alloys and 0.2 to 3% by weight of metallic boron powder are added, and the mixture is heated to at least 1250°C in the diamond stability region of the graphite-diamond pressure-temperature phase diagram. The above is the method of sintering.

“In this case, it is preferable to mix graphite or non-diamond carbon in a volumetric ratio of 30 or less into the main raw material.

Cobalt, iron, nickel, or an alloy thereof mixed in the method of the present invention serves to prevent graphitization of diamond grains and to convert non-diamond carbon, if present, to diamond.

When the amount added is less than 2% by weight, the effect is small, and when it exceeds 200% by weight, several 10 to 100 particles are present in the sintered body.
A micrometer-sized metal pool or vein-like J structure remains, reducing the strength of the sintered body, and particles falling from the metal pool portion during cutting.

In addition, the metallic boron mixed suppresses grain growth of diamond particles, prevents particles from falling off during cutting, and prevents deterioration of wear resistance and toughness.

What is the amount added? If it is less than 0.2% by weight, the effect is small, and if it exceeds 3% by weight, grain growth cannot be suppressed, and large diamond particles can be seen in the sintered body.

Therefore, the amount of boron added should be in the range of 0.2 to 3% by weight, preferably 0.8 to 2% by weight, and the diamond particles should be several microns.
It was experimentally confirmed that it does not grow beyond m.

According to the present invention, there is an excellent effect that a sintered body having a density of 95 coefficients or more of the theoretical density can be obtained.

The present invention will be explained in detail below with reference to Examples.

Example 1 8% by weight of cobalt powder and 1.2% by weight of boron powder were added to natural diamond powder with an average particle size of 1 μm or less, mixed thoroughly, and heated to 63Kb at 1450°C.
It was sintered for 15 minutes.

The obtained sintered body was a black dense body, had a density of 98% or more of the theoretical density, and had an average grain size of about 4 μm.

This sintered body was processed into a chip shape (5PP422) at the same speed of 500 m/min, depth of cut Q, 3 man, and feed 0.
When cutting tests were conducted on Al-8i alloy and pure A7 under conditions of , 1 man/rev, a good cut surface with a finished surface of 1.5S or less was obtained.

Example 2 A strong diamond sintered body having an average grain size of 5.3 μm was obtained under the same conditions except that the first additive, cobalt, was replaced with iron.

Example 3 Cobalt, the first additive in Example 1 above, was replaced with nickel, and the other conditions were the same, with an average particle size of 3.8 μm.
A strong diamond sintered body was obtained.

However, when the first additive was nickel, when the microstructure of the sintered body was observed, abnormal growth structures in which diamond particles extended in one direction were observed in some places.

Example 4 12% by weight of cobalt powder was added to the same main raw material as in Example 1, and the mixture was treated at 1530° C. and 64 Kb for 15 minutes to obtain a diamond sintered body.

This relative density was 93%, and the average particle size reached 100 μm or more, confirming that diamond particles would grow large unless the second additive, boron, was added.

Further, when this sintered body was processed into a chip shape and a cutting test was conducted under the same conditions as in Example 1, a finished surface 3S was obtained.

Moreover, the life of the cutting edge was about half that of Example 1.

Example 5 For synthetic diamond powder with an average particle size of 1 μm or less, the amount of boron as the second additive was fixed at 1.5% by weight, and the results of changing the first additive are shown in the table below. show.

All of these sintered bodies were strong sintered bodies with an average particle size of 7 μm or less, and cutting performance comparable to that of Example 1 was obtained.

Example 6 The main raw material was synthetic diamond powder with a particle size of 2 to 5 μm, to which 17 parts by volume of graphite powder was added, and to this, 10 parts by weight of cobalt was added as the first additive, and 10 parts by weight of cobalt was added as the second additive. As a material, 1.5 weight percentage of boron is added and mixed, 63K
After sintering at 1570°C for 15 minutes, a strong sintered body with a theoretical density of 97 was obtained.

Note that the average diameter of diamond particles in the sintered body is approximately 12μ.
It was m.

Example 7 In Example 6, a sintered body was obtained using the same material as the main raw material except that the amount of graphite powder added was increased by 30 weight, and the other conditions were the same.

The average grain size of the sintered body was about 25 μm, and the wear resistance was slightly inferior to that of Example 1.

Claims (1)

[Claims] 1 Synthetic or natural diamond particles, or mixtures containing graphite or non-diamond carbon with a volume ratio of 30 or less, from whole blood powders of cobalt, nickel or iron, or metal powders thereof, with a volume ratio of 2 to 20'. Alone or together with two or more of the alloys, 0.2 to 3
A diamond sintered body characterized in that metal boron of a weight ratio is mixed and the resulting mixture is sintered at a temperature of at least 1250°C or higher under the diamond stability region of the graphite-diamond pressure-temperature phase diagram. Manufacturing method.