FRACTURE MECHANISMS OF CERAMIC COATINGS IN INDENTATION

Indentation tests on ceramic coatings are carried out in this paper an d fracture pattern diagrams as a function of normal load and coating t hickness are introduced for Al2O3 and TiN coatings deposited on cement ed carbide substrates. Ring cracks are observed in indentation with a blunt indenter (1.5 mm radius), while lateral and radial cracks are ob served in indentation with a sharp indenter (0.2 mm radius). The mecha nisms for generating ring and lateral cracks are analyzed using elasti c theory and equations predicting the critical loads for crack generat ion are introduced. The effective elastic modulus E(eff), is introduce d for this analysis as a new elastic parameter for a coated surface. T he results show that the theoretically calculated critical loads for c rack generation agree well with the experimental ones.