Fracture toughness of TiC-coated cemented carbides

Abstract

Cemented carbide samples were coated with TiC layers of various thicknesses by the chemical vapour deposition process. The transverse rupture strength (TRS) of the coated material was determined and found to decrease with increasing thickness of the brittle TiC coating. A theory based on fracture mechanics has been developed and is shown to fully account for the observed behaviour. From the variation of TRS with coating thickness the K _1C value of the cemented carbide substrate and the size of its plastically deformed zone can be calculated to a high accuracy. K _1C values determined by this method agree well with values obtained by other methods.