MACHINING OF TiB2AND ITS COMPOSITES

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Abstract
The mechanism of material removal during electrical discharge machining (EDM) of TiB2 and its composites was studied by examining surfaces and debris using electron microscopy and X-ray diffraction. In TiB2, melting occurs due to formation of eutectic liquid with present impurities. In TiB2-laminates melting and creation of high residual stresses produced cracks and fissures. The surface hardness was comparable to that obtained by polishing. During EDM of BN-TiB2 composites, TiB2 forms eutectic liquid at the interface with BN, and residual BN and some TiB2 spall due to thermal shock. During pause periods parts of the liquid and fragments are flushed out by the dielectric. Composites rich in TiB2 or with fine TiB2 grains gave high material removal rates due to their high electrical conductivity. For all BN-TiB2 composites, the diamond saw yielded much higher material removal rates than EDM but, unlike EDM, the diamond saw gave relatively lower removal rates for compositions rich in TiB2, and for composites with fine TiB2 grains due to their high hardness.

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