JPS631272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a silicon nitride member manufactured by electric discharge machining and a method for manufacturing the same. Sintered silicon nitride (hereinafter abbreviated as Si ₃ N ₄ ) has attracted attention as a material with excellent oxidation resistance, low coefficient of thermal expansion, _and high high _- temperature strength. Research and development are being actively conducted to use it as a high-temperature structural material such as for heat exchangers, nozzles, and heat exchanger components. But this
Since Si ₃ N ₄ sintered bodies are usually made by powder metallurgy, it is difficult to obtain complex shapes for sintered bodies, and it is difficult to obtain precise dimensions and surface accuracy.
The product is made from a Si ₃ N ₄ sintered body that undergoes mechanical processing such as grinding. However, as is well known, Si ₃ N ₄ is a highly hard material that is difficult to machine, requiring a great deal of time and effort, and can only be machined into relatively simple shapes. Various limitations in processing technology have hindered the expansion of the applications of Si ₃ N ₄ , such as the impossibility of obtaining thin-walled parts such as blades by machining. Although it is generally known that electrical discharge machining is one of the means for manufacturing complex shapes, it has been conventionally believed that Si ₃ N ₄ is a perfect insulator and cannot be subjected to electrical discharge machining. In view of the above, the present invention was developed to solve such problems, and the gist of the present invention is as described in the claims. The present invention will be described in detail below. The present inventors have studied various methods to enable electric discharge machining of Si ₃ N ₄ . Of course, it is easy to imagine that electrical discharge machining becomes possible if a large amount of electrically conductive material is added to Si ₃ N ₄ . However, in this case, the properties of Si ₃ N ₄ will be greatly affected depending on the substance added and its amount. For example, when adding metals with good electrical conductivity such as Cu or Ni
Si ₃ N ₄ has poor wettability and cannot be sintered sufficiently, making it impossible to obtain sufficient strength. On the other hand, Al ₂ O ₃ ,
When well-known additives such as Y ₂ O ₃ and MgO are added, electrical conductivity does not improve because the additives have low electrical conductivity, making electrical discharge machining impossible. Therefore, the present inventors investigated additive substances that would improve the electrical conductivity without significantly changing the properties of Si ₃ N ₄ and added oxides, carbides, and
Nitride, boride and compounds of two or more of these
I came up with the idea that it would be good to add one or more selected from AIN and Al ₄ C ₃ . As is well known, the oxides, carbides, nitrides, and borides of Group A, A, and A elements are highly hard materials and have little strength loss at high temperatures.They form solid solutions with each other in a wide composition range, and the properties of the solid solutions There is no big difference between them. _AIN , _Al4C3
There is also little strength loss at high temperatures. However, although these materials have high high-temperature strength, they are at a low level compared to Si ₃ N ₄ , and their oxidation resistance is also inferior, so adding these materials will naturally deteriorate the high-temperature properties of Si ₃ N ₄ . . Therefore, the amount added should be limited to the smaller side. The inventors conducted experiments on this point and surprisingly found that the volume ratio of these substances was
It was discovered that if 0.5% or more is added and sintered, the electrical conductivity of the Si ₃ N ₄ sintered body increases rapidly to 10 ^-3 Ω ^-1 cm ^{-1 or} more, making electrical discharge machining possible. . 1st
In the figure, the change in electrical conductivity depending on the amount of TaN added to Si ₃ N ₄ is indicated by A. The theoretical value B in the figure is expressed as below.
Calculated based on Maxwell's equation. θ _tptal = σ _Si3N4 × [σ _TaN +2σ _Si3N4 −2V _TaN (σ _Si
3N4 −σ _TaN )]/[σ _TaN −2σ _Si3N4 +V _TaN (σ _Si3N4 −
σ _TaN )] However, σ _Si3N4 is the electrical conductivity of Si ₃ N ₄ , and σ _TaN is TaN
The electrical conductivity of V _TaN indicates the volume ratio of TaN. In addition, in the Si ₃ N ₄ sintered body of the present invention, the additive substance becomes a dispersed structure as a second phase even after sintering, but the electrical conductivity of the Si ₃ N ₄ sintered body is in this way compared to the theoretical value. The reason why it is so excellent is thought to be due to the following two reasons. (1) All or part of the second phase particles dispersed in the Si ₃ N ₄ matrix are Si ₃ N ₄ of the Matrix.
A composite phase with good conductivity is formed by diffusion and reaction around the particles, and the continuity of this composite phase improves the conductivity of the Si ₃ N ₄ sintered body. (2) When the volume ratio of the second phase particles dispersed in the Si ₃ N ₄ matrix exceeds 25%, the conductivity of the Si ₃ N ₄ sintered body increases due to the contact between the second phase particles. Improves sex. Among the reasons for electrical conductivity mentioned above, when the volume ratio of the second phase particles is 25% or less, only (1) is the main effect, and when the volume ratio exceeds 25%, (1) + (2) This is considered to be the effect of The preferable addition amount of this second phase particle is expressed as a 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 Si ₃ N ₄ sintered body is insufficient and electrical discharge machining cannot be performed, and if the amount added is more than 30%, the high temperature strength of the Si ₃ N ₄ sintered body is This is due to a sudden drop in It should be noted that in producing the Si ₃ N ₄ sintered body to be subjected to electrical discharge machining, the average particle size of the Si ₃ N ₄ powder and additive material must be 1.0 μm or less. This is because if the average particle size is 1.0 μm or more, it is difficult to disperse the additive material uniformly during mixing, and therefore a sufficiently uniform and conductive composite phase is not formed during sintering.
This is because the electrical conductivity of the Si ₃ N ₄ sintered body does not improve. Examples of the present invention are shown below. Example 1 Si ₃ N ₄ powder (particle size 0.8 μm) with various volume ratios
After adding TaN and TiC (both particle size 0.5 μm) and thoroughly mixing them, the electrical conductivity of the Si ₃ N ₄ sintered body was sintered under pressure at 200 kg/cm ² at 1700°C for 30 minutes. were measured, and it was determined whether electrical discharge machining was possible. This is shown in Tables 1 and 2. The electrical discharge machining conditions are a machining current of 0.2A and a pulse width of 1.2μS.
It is.

【table】

[Table] Example 2 Si ₃ N ₄ powder (particle size 0.8 μm) with various volume ratios
Add HfN and TaC (both particle size 0.5 μm),
After thorough mixing, the Si ₃ N ₄ sintered body was sintered at 1700°C under a nitrogen partial pressure of 5 kg/cm ² , and the anti-stress strength at 1000°C was measured. It is shown in Tables 3 and 4. The bending strength is 10mmspan, and the loading rate is 0.5.
Measured under mm/min conditions.

【table】

[Table] Example 3 Various additives added to Si ₃ N ₄ powder at 3% volume ratio
After adding and mixing thoroughly, 1700℃ x 30 minutes 200Kg/
The electrical conductivity of each Si ₃ N ₄ sintered body obtained by pressure sintering under cm ² conditions was measured to investigate whether electrical discharge machining was possible. The results are shown in Table 5.

[Table] Example 4 Sintering was performed while changing the average particle diameter of the Si ₃ N ₄ powder and additive particles, and the electrical conductivity and electrical discharge machinability of the sintered bodies were investigated. It is shown in Table 6.

【table】 [Brief explanation of the drawing]

FIG. 1 illustrates a diagram showing a change in electrical conductivity of a Si ₃ N ₄ sintered body due to the addition of TaN. A...actual value, B...theoretical value.

Claims (1)

[Claims] 1. 0.5 to 30% a, a, a by volume
By adding oxides, nitrides, carbides, borides, and compounds of two or more of these elements and one or more selected from AlN and Al ₄ C ₃ , the electrical conductivity can be increased.
Silicon nitride parts that can be electrically discharged to a resistance of 10 ^-3 Ω ^-1 cm ^-1 or higher. 2 0.5 to 30% a, a, a by volume
By adding oxides, nitrides, carbides, borides, and compounds of two or more of these elements and one or more selected from AlN and Al ₄ C ₃ , the electrical conductivity can be increased.
In manufacturing a silicon nitride member that can be electrically discharge-machined to a resistance of 10 ^-3 Ω ^-1 cm ^-1 or more, the silicon nitride member is characterized in that the silicon nitride and additives are powders with an average particle size of 1 μm or less. Manufacturing method.