Fracture Mechanisms of Ceramic Coatings in Indentation

Indentation tests on ceramic coatings are carried out in this paper and fracture pattern diagrams as a function of normal load and coating thickness are introduced for Al₂O₃ and TiN coatings deposited on cemented carbide substrates. Ring cracks are observed in indentation with a blunt indenter (1.5 mm radius), while lateral and radial cracks are observed in indentation with a sharp indenter (0.2 mm radius). The mechanisms for generating ring and lateral cracks are analyzed using elastic theory and equations predicting the critical loads for crack generation are introduced. The effective elastic modulus E_eff, is introduced for this analysis as a new elastic parameter for a coated surface. The results show that the theoretically calculated critical loads for crack generation agree well with the experimental ones.