Effect of hexagonal-BN additions on the sliding-wear resistance of fine-grained α-SiC densified with Y3Al5O12 liquid phase by spark-plasma sintering

The effect of flaky hexagonal (h) BN additions (1, 5, and 10 vol.%) on the lubricated sliding-wear behavior of fine-grained, liquid-phase-sintered SiC ceramics fabricated by spark-plasma sintering was investigated. It was found that resistance to the initial mild, deformation-controlled wear decreases with increasing h-BN content in the composite, which progressively exhibits a greater wear rate and a sooner transition to severe wear. This is because the softer h-BN particles reduce the hardness and do not act as internal lubricant, while promoting poorer grain cohesion due to their morphologically-favored segregation at grain boundaries. By contrast, their addition is increasingly beneficial in terms of resistance to the subsequent severe, fracture-controlled wear upon prolonged sliding contact, with a lower wear rate. This is because the flaky h-BN particles increase the fracture toughness, and also act efficiently as external lubricant when pulled-out from the microstructure. Finally, implications for the design of advanced triboceramics are discussed.