JPH0225865B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-density and high-strength B ₄ C sintered body and a method for manufacturing the same. Boron carbide is a hard material second only to diamond, and has a low density and chemical stability.Its uses include nozzles, seal rings, dresser abrasives, and equipment parts for handling strong acids. Sintering is difficult due to its high melting point, and a satisfactory sintered body cannot be obtained simply by sintering boron carbide powder at a temperature close to its melting point. Therefore, the conventional method of adding metal to boron carbide powder and sintering it has a bending strength of 60 kg/
A sintered body with a size of mm ² or more was obtained, but because the boron carbide was bonded with metal, it had the disadvantage of being significantly inferior in strength and wear resistance in high temperature ranges. In addition, instead of sintering by metal bonding, boron carbide is sintered by the hot press method, which uses a graphite mold and sinters under pressure at a temperature of 2100°C or higher. Since sintering is possible without adding any additives, the resulting boron carbide compact retains the excellent properties of boron carbide, but the sintering temperature exceeds 2000℃, causing wear and tear on the graphite mold and damage to equipment. The manufacturing cost is high, and the crystal grains grow, resulting in coarse crystals, and the bending strength is approximately
Its use was limited due to its low impact strength of 50Kg/mm ² and low impact strength. The present invention eliminates the above drawbacks and provides high density and high strength.
The purpose of the present invention is to provide a B ₄ C sintered body and a method for manufacturing the same, and the gist thereof is to contain 1 to 10% by weight of silicon nitride,
The remainder consists of boron carbide, and its relative theoretical density is 98.5.
% or more and a grain size of 10 μm or less, and a raw material powder consisting of 1 to 10% by weight of silicon nitride and the balance boron carbide is hot-press sintered. The sintering temperature in this case is
A temperature of 1900 to 1950°C is preferred. According to the present invention, B ₄ C, which is considered difficult to sinter, can be made into a sintered body having a density of 98.5% or more of the theoretical density. Examples that led to the development of the present invention will be described below. Example 1 B ₄ C powder with purity of 99.5% and average particle size of 3 μm and purity
A mixture of various Si ₃ N ₄ powders with a 99.5% average particle size of 5 μm in the proportions listed in Table 1 was wet mixed and pulverized using a ball mill mixer for 10 hours, and then thoroughly dried to obtain a raw material for sintering. Fill a 50 x 50 (mm) square graphite mold with a height of 60 mm with the various sintering materials mentioned above, insert it into a high-frequency coil, and produce 200 kg/kg at each predetermined temperature within the temperature range of 1850 to 2000°C. A pressure of cm ² was applied and maintained for 60 minutes, then the pressure was released and the mixture was allowed to cool to obtain a desired sintered body measuring 50×50×5.5 (mm). Each sintered body was cut and ground with a diamond grindstone to create four 3 x 4 x 36 (mm) test pieces, and the measured values obtained from various tests were also used for the first
Shown in the table.

[Table] The results of measuring the theoretical density, particle size, and Charpy impact value of the test piece of sample No. 1 in Table 1 above, which was sintered at 2100°C, 200Kg/cm ² , and for 60 minutes. is the theoretical density 97.2%, particle size
The diameter was 40 μm, and the Shalpy impact value was 0.06 Kg·m/cm ² . Example 2 The sample sintered at a temperature of 1950°C in Example 1 was
Cut into a 10 x 5 (mm) plate with a diamond grindstone,
Surface grinding is done with a No. 200 diamond whetstone to 10×
Abrasive grains (Metecolite C, No. 40) were sprayed at a spray distance of 50 mm at an air pressure of 5 Kg/cm ² on a 10 (mm) surface using a sandblasting machine having a nozzle with an inner diameter of 8 mm, and the weight loss was measured. The results are shown in Table 2.

[Table] From the results of the above examples, the following can be seen. i.e. B ₄ C
Powders sintered with Si ₃ N ₄ powder added have improved sinterability compared to those without additives, and can be heated at 1900℃.
Despite sintering at a relatively low temperature, this value is quite high. In other words, for sample No. 1, the temperature was 2000℃.
Even those sintered using the method of the present invention were still poorly sintered, so the temperature was further increased to 2100°C for sintering, but as mentioned above, the Charpy impact value was significantly lower than that of the method of the present invention. On the other hand, even when Si ₃ N ₄ is added, a Si ₃ N ₄ addition amount of 0.5% by weight is not sufficiently sintered even at a hot press temperature of 1850 to 2000°C, so 1% by weight or more is required. On the other hand, if it exceeds 12% by weight, it will not be possible to obtain a Charpy impact value of 0.15 Kg·m/cm ² or more and the toughness will be lost. For these reasons, the amount of Si ₃ N ₄ added is preferably 1 to 10% by weight. As described above, the sintered body according to the present invention has a dense and fine crystal structure, and is satisfactory for use as nozzles, seal rings, dresser abrasives, liners for jet crushers, etc. It has the required strength.

Claims (1)

[Scope of Claims] 1 Consisting of 1 to 10% by weight of silicon nitride and the remainder boron carbide, its relative theoretical density is 98.5% or more, and its crystal grain size is
Sintered body of 10μm or less. 2. A method for producing a sintered body, which comprises hot press sintering raw material powder consisting of 1 to 10% by weight of silicon nitride and the balance boron carbide.