INDENTATION AND MICROCUTTING FRACTURE DAMAGE IN A SILICON-CARBIDE COATING ON AN INCOLOY SUBSTRATE

The fracture damage morphology for static indentation tests and contro lled microcutting tests using a Vickers indentor was investigated for an amorphous silicon carbide coating deposited on an Incoloy substrate . Crack initiation thresholds were detected for both testing modes usi ng an acoustic emission sensor. The fracture damage morphology for sta tic indentation consisted of Hertzian-like cracks surrounding the inde ntation site with no lateral crack-chipping occurring up to the maximu m indentation load of 8 N. In contrast, microcutting generates lateral cracks at the microcutting groove entrance for loads as low as 0.3 N. For loads up to 1 N, the groove damage was confined to the 5 mu m thi ck coating and the fracture response is similar to that occurring in a monolithic brittle solid. At higher loads, extensive lateral crack ch ipping occurred along the microcutting grooves accompanied by coating decohesion at the root of the chip.