Silicon nitride ceramics containing more than 10wt% silicon carbide whisker can be machined electro discharge because of the low electrical resistivity of less than 103Ω·cm. Machining properties of Si3N4-SiC whisker composite ceramics by the ram-type electrical discharge machining have been studied. Pure copper is used as a tool electrode. Cutting rate of this composite ceramics increases with an increase in machining current. The cutting rate in reverse polarity machining for positive tool electrode is two or three times larger than that in normal polarity machining. The machined surface in the normal polarity machining is rather smooth, while large craters develop on the surface in the reverse polarity machining. Surface roughness after machining is more than 10μm. The wear rate of the copper tool electrode is less than 10%. Silicon carbide formed probably by the decomposition of the ingredients in this composite ceramics and kerosene used as machining oil adheres to the tool electrode, which improves the wear resistance of the tool electrode.
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Tamari et al. (1986) studied this question.