MECHANICAL FAILURE OF THIN BRITTLE COATINGS

Thin brittle layers are deposited or developed on component surfaces for a variety of reasons. In many practical applications the layers are stressed by internal residual stresses (due to growth, deposition processes or thermal transients) or by externally applied loads. Under such conditions, coating failure can occur, which may consist of through-thickness cracking and/or cracking along (or parallel to) the coating substrate interface. This paper reviews proposed mechanisms and models for cracking and spallation of thin brittle coatings, specifically due to differential strains between the coating and substrate. Failure of coatings on flat substrates, under tensile or compressive stress, is discussed and the effect of surface curvature is addressed.