JPS631271B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a silicon carbide member using electrical discharge machining. Sintered silicon carbide (hereinafter referred to as SiC) has attracted attention as a material with excellent oxidation resistance, low coefficient of thermal expansion, and high strength at high temperatures. Research and development is being actively conducted to use it as a high-temperature structural material such as. However, since this SiC sintered body is usually made by powder metallurgy, it is difficult to obtain a sintered body with a complex shape, and it is difficult to obtain one with precise dimensions and surface accuracy. The reality is that parts with a predetermined shape and precision are obtained by adding machining such as grinding after sintering. However, as is well known, SiC
is a highly hard and brittle material,
Machining is difficult and requires a large amount of time, and only relatively simple shapes can be obtained. Furthermore, cracks are likely to occur during processing, resulting in poor manufacturing yield. Furthermore, some thin-walled parts such as turbine blades cannot be manufactured even by such machining. These limitations in processing technology are one of the major obstacles to expanding the applications of SiC, which has a variety of excellent properties. In addition to machining, laser machining, arc discharge machining, and electrical discharge machining are known as methods for manufacturing components with complex shapes, but the former is limited to drilling of thin materials and is extremely difficult to produce thick materials with complex shapes. Also, regarding electric discharge machining, SiC has poor electrical conductivity, so high voltage corona discharge
It is only possible to make small holes of φ or less, or even if arc discharge is possible, the machining efficiency is extremely poor, and electric discharge machining takes a lot of time, so it has not been generally adopted. As a result of various studies on methods for easily performing electrical discharge machining of SiC sintered bodies, the present inventors found that while maintaining the original excellent characteristics of SiC, electrical conductivity is imparted to a degree that enables easy electrical discharge machining. I found a way. With common sense, it is easy to imagine that adding a large amount of electrically conductive material to SiC will improve electrical discharge machinability. However, in most cases, the properties of SiC itself were usually greatly affected. For example, when metals such as Cu and Ni, which are good conductors, are added, these metals have poor wettability with SiC and cannot be sintered sufficiently, resulting in a failure to obtain high strength and, of course, significantly lowering the hardness. On the other hand, when Si ₃ N ₄ , Al ₂ O ₃ and the like are added, the strength is sufficient, but there is no improvement in electrical conductivity and it is impossible to improve electrical discharge machinability. Therefore, the present inventors investigated additive substances that improve the electrical conductivity while maintaining the properties of SiC, and found that carbides, nitrides, and
It has been found that it is sufficient to add one or more selected from borides, oxides, compounds of two or more thereof, and Al ₄ C ₃ . As is well known, the various compounds of Group A, A, and A elements are highly hard materials and exhibit little strength loss at high temperatures, and they form solid solutions with each other over a wide range, and the properties of the solid solutions are not significantly different from each other. Furthermore, Al ₄ C ₃ also exhibits little strength loss at high temperatures. However, although these additive substances have high high-temperature strength, they are at a lower level than SiC and have inferior oxidation resistance, so adding these substances naturally deteriorates the high-temperature properties of SiC. Therefore, its addition should be limited to smaller amounts. The present inventors conducted a prototype experiment on this point and surprisingly found that if 0.5% or more of these substances were added by volume, the electrical conductivity of the SiC sintered body increased rapidly, reaching 10 ^-2 It has been found that electrical discharge machining becomes extremely easy when the resistance is Ω ⁻¹ cm ⁻¹ or more. As an example, FIG. 1 shows the change in electrical conductivity of a sintered body depending on the amount of TaN added to SiC. The theoretical value 2 in the figure is calculated based on Maxwell's equation expressed by the following formula. 1 is an actual measurement value. σ _Tptal = σ _SiC × [σ _TaN +2σ _SiC −2V _TaN (σ _SiC −
σ _TaN )] / [σ _TaN −2σ _SiC +V _TaN (σ _SiC −σ _TaN )]
However, σ _Tptal , σ _SiC , and σ _TaN are sintered bodies, SiC, and σ TaN, respectively.
Electrical conductivity of TaN, V _TaN indicates the volume ratio of TaN. In addition, in the SiC sintered body of the present invention, the additive substance remains in a dispersed structure as a second phase even after sintering, but the electrical conductivity 1 of the SiC sintered body is extremely high compared to the theoretical value 2. This is thought to be due to the following two reasons. (1) All or part of the second phase particles dispersed in the matrix in SiC diffuse and react around the SiC particles in the matrix to form a composite phase with good conductivity, but this composite phase is continuous. This improves the conductivity of the SiC sintered body. (2) When the volume ratio of the second phase particles dispersed in the SiC matrix exceeds 25%, the second phase particles come into contact with each other, thereby improving the conductivity of the SiC sintered body. Among the reasons for electrical conductivity mentioned above, if the volume ratio of the second phase particles is 25% or less, only the effect of (1) above is mainly effective, and if the volume ratio exceeds 25%, the effect of (1) above is the main reason.
The effect of +(2) is considered. The preferable addition amount of the second phase particles is as follows in terms of volume ratio:
It is 0.5% or more and 30% or less. The reason for this is that if the amount added is less than 0.5%, the electrical conductivity of the SiC sintered body is insufficient and electrical discharge machining cannot be performed efficiently.
If the amount added is above, the high temperature strength of the SiC sintered body will decrease rapidly. Please note that:
In manufacturing this SiC sintered body with good electrical discharge machinability, the average particle diameter of the SiC powder and the additive material are both
It is preferably 1 μm or less. This is because if the average particle size is 1 μm or more, it is difficult for the additive to be dispersed uniformly during mixing, and therefore a uniformly conductive composite phase is not formed during sintering, resulting in a decrease in the electrical conductivity of the SiC sintered body throughout the member. It is difficult to perform electrical discharge machining smoothly because the improvement is not uniform. Note that the object of the present invention can be achieved by sintering by any of the usual sintering of a powder compact, hot press sintering under pressure, and hot static pressure molding. Next, a detailed explanation will be given with reference to examples. Example 1 After adding TaN and TiC with a particle size of 0.5 μm in the volume ratio shown in Table 1 to SiC powder with an average particle size of 0.8 μm and thoroughly mixing them, the mixture was heated at a pressure of 200 Kg/cm ² at 1700°C
The electrical conductivity was measured for SiC sintered bodies that were pressure sintered in minutes, and the ease of electrical discharge machining was compared.
The results are shown in Table 1. The electrical discharge machining conditions were a machining current of 0.2 A and a pulse width of 1.3 μs. In the table, "possible electrical discharge machining" means that electrical discharge machining is possible under the above conditions, "poor" in machining efficiency means that the electrical discharge machining efficiency is extremely poor, and "good" means that machining is sequentially efficient. Indicates that things went smoothly. TiC40
When the product was examined after processing, it was found that chipping had occurred partially, indicating that the strength was quite low.

[Table] Example 2 TiB ₂ and HfN powders with a particle size of 0.6 μm were added to SiC powder with an average particle size of 0.8 μm in the volume ratio shown in Table 2, thoroughly mixed, and then molded at a temperature of 1700°C and a nitrogen content. Regarding the SiC sintered body sintered under a pressure of 5Kg/ ^cm2 ,
The bending strength at 1000°C was measured. The results are shown in Table 2. Note that the bending strength was measured under the conditions of a 10 mm span and a loading rate of 0.5 mm/min.

【table】

[Table] As can be seen from this table, the bending strength decreases rapidly when the amount added is 40%. Regarding electrical discharge machinability,
Efficient electrical discharge machining was possible with both TiB ₂ and HfN at 0.5% or more, but with 40% HfN chipping occurred and a machined product with a good shape could not be obtained. Example 3 Powders of various additives shown in Table 3 (particle size 0.1 to 0.9 μm) were added to SiC powder with an average particle size of 0.5 μm at a volume ratio of 3
% addition and mixing, the electrical conductivity of the obtained SiC sintered body was measured by pressure sintering under the conditions of a pressure of 200 Kg/cm ² and a temperature of 1700°C for 30 minutes, the same as in Example 1. The quality of electrical discharge machinability was examined under various conditions. The results are shown in Table 3. All of the sintered bodies shown in Table 3 had good electrical discharge machinability. The appearance after processing was also good with no chips or chips.

【table】

[Table] Example 4 Sintering was carried out under the same conditions as in Example 3, with the average particle diameters of the SiC powder and additive powder changed as shown in Table 4, and the electrical conductivity and The quality of electrical discharge machinability was investigated. The amount of additives was 3% by volume in each case. The results are shown in Table 4.

【table】

[Table] ○: Good electrical discharge machining performance △: Electric discharge machining is possible but unstable

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the content of the present invention.
FIG. 3 is a diagram showing the relationship between the amount of TaN added to SiC and the electrical conductivity. 1: Actual measurement value, 2: Theoretical calculation value.

Claims (1)

[Claims] 1. Carbides and nitrides of group a, group a, and a elements,
A powder consisting of at least one selected from the group consisting of borides, oxides, compounds of two or more of these, and Al ₄ C ₃ is added to and mixed with silicon carbide powder at a volume ratio of 0.5 to 30%. 1. A method for manufacturing a silicon carbide member, comprising: press-molding and sintering a mixed powder, or press-sintering a sintered body to form a sintered body, and forming the sintered body into a predetermined shape by electrical discharge machining. 2. The method for manufacturing a silicon carbide member according to claim 1, wherein the silicon carbide powder and the additive material powder each have an average particle size of 1 μm or less. 3. Claim 1, wherein the sintered body has an electrical conductivity of 10 ^-2 Ω ^-1 cm ^-1 or more.
A method for manufacturing a silicon carbide member according to item 1 or 2.