JPH0143705B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ceramic sintered body that has sufficient electrical conductivity for electric discharge machining and is capable of electric discharge machining. In recent years, research and development has been actively promoted to utilize ceramic products that utilize the excellent heat resistance and heat shielding effect of ceramics as high-temperature structural materials such as turbine engine blades and nozzles, or heat exchanger components. . However, because these ceramics can only be obtained in extremely simple shapes due to limitations in the sintered body manufacturing technology, products are often finished by mechanical processing after sintering. In other words, it is fine if the ceramic sintered body can be used as is, but in most cases machining is required. Particularly in the case of the above-mentioned parts, dimensional accuracy and complicated shapes are required, and it takes a lot of time. Currently, the finishing process is performed over and over again.
However, as is well known, ceramic sintered bodies have extremely high hardness and are brittle, making it extremely difficult to process them. Therefore, the present inventors conducted repeated research to improve the rough machinability of conventional ceramic sintered bodies, and as a result, they arrived at the present invention. The present inventors focused on electric discharge machining among various machining methods, and as a result of examining various methods of imparting conductivity to non-conductive ceramics, which were conventionally thought to be impossible to perform electric discharge machining, the inventors found that non-conductive It has been discovered that by forming a second ceramic phase with good conductivity in a sintered ceramic, a ceramic sintered body with good conductivity to the extent that electric discharge machining is possible can be obtained. Examples of non-conductive ceramics include Al ₂ O ₃ ,
Si ₃ N ₄ , ZrO ₂ , MgO, etc. are used as structural members because of their heat resistance and strength. In the present invention, ZrO ₂ is used as the non-conductive ceramic. This is because it has excellent high temperature strength and wear resistance. As the second phase conductive ceramics,
There are carbides and nitrides of groups in the periodic table such as TiC and TaC, but TiC is optimal in combination with ZrO ₂ . There are two possible reasons why this combination of two phases provides conductivity. First, all or a portion of the dispersed second phase particles react with the matrix phase particles to form an electrically conductive composite phase around the matrix phase particles, but this composite phase is continuous. This improves the conductivity of the ceramic sintered body. Second, the volume fraction of the second phase particles to be dispersed is 5%.
When the value exceeds 1, the electrical conductivity of the ceramic sintered body is improved because the electrically conductive second phases come into contact with each other. Among the above two reasons, when the volume fraction of the added second phase is small, the first effect is obtained, and when the volume fraction exceeds 5%, the conductivity is obtained due to the first and second effects. Conceivable. For the above reasons, conductivity suitable for electrical discharge machining cannot be obtained unless the second phase TiC is 40% by volume or less. ZrO ₂ −TiC with various conductivities in terms of electrical discharge machinability
As a result of investigating the sintered body, the electrical conductivity was 10 ^-3
It was found that sintered bodies with Ω ^-1 cm ^-1 or more and 10 ⁴ Ω ^-1 cm ^-1 or less have good workability and finishing accuracy. Even if electric discharge machining is possible, if the finishing accuracy is poor, further re-polishing will be required, and the characteristics of machining complex shapes will be lost. If the electrical conductivity becomes too high at this point, a chipping phenomenon will occur on the machined surface, and the surface roughness (μm, Rmax) will deteriorate, requiring repolishing. Next, an example will be explained. Example 1 TiC with various volume fractions shown in Table 1 in ZrO ₂ powder
After adding the powder, mix thoroughly and heat at 1350℃ for 30 minutes.
The electrical conductivity of ceramic sintered bodies obtained by hot pressing under conditions of 200 Kg/cm ² and 200 Kg/cm 2 was measured, and the presence or absence of electrical discharge machinability was investigated. The results are shown in Table 1. As a result, electrical discharge machining was possible for materials with electrical conductivity of 10 ^-3 Ω ^-1 cm ^-1 or higher. Electric discharge machining conditions: Machining current 0.2A Pulse width 1.3 Pause time 0.5

[Table] In Example 1, conductivity can be obtained even if TiC is 40% by volume or more, but the strength as a structural member, which is the purpose of the present invention, is lowered, there are problems in terms of oxidation resistance, and even during electrical discharge machining. There were thin nicks, making precise electrical discharge machining difficult. Example 2 ZrO ₂ −Y ₂ O ₃ (5 mol%) prepared by coprecipitation method
After adding TiC powder with the volume percentage shown in Table 2 to the powder, it was thoroughly mixed using a ball mill, and this was mixed in a vacuum.
The electrical conductivity of the sintered body obtained by hot pressing at 1450° C. for 1 hour under a pressure of 200 kg/cm ² was measured, and the presence or absence of electrical discharge machinability was investigated. The results are shown in Table 2. It was possible to have an electrical conductivity of 10 ^-3 Ω ^-1 cm ^-1 or higher.

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Claims (1)

[Claims] 1 The main component is non-conductive _ZrO2 , and it contains less than 40% and more than 5% TiC by volume as a conductive ceramic phase, so that it has electrical conductivity in the state of a sintered body.
A ceramic sintered body capable of electric discharge machining, characterized in that it has an electrical conductivity of 10 ^-3 Ω ^-1 cm ^-1 or more and 10 ⁴ Ω ^-1 cm ^-1 or less and can be subjected to electric discharge machining.