MICROSTRUCTURAL RESPONSE OF MONO-AND MULTILAYER HARD COATINGS DURING INDENTATION MICROHARDNESS TESTING

An investigation of indentation crack patterns and the nature of fract ure mechanisms of hard coatings can provide useful information to aid in the understanding of failure mechanisms occurring as a result of sc ratch and wear tests. Examples of several different types of single an d multilayer coating systems are presented in this study. The effect o f substrate and microstructure on the brittle-ductile transition behav iour is discussed. The concept of energy dissipation is introduced to interpret deformation and fracture behaviour during indentation tests. If a hard coating undergoes some densification or plastic flow to dis sipate a proportion of the energy, then the premature adhesive failure due to the non-compliance of the strain al hard coating/substrate int erface can be avoided. The compaction or plastic flow of the hard coat ing also effectively disperses concentrated stress and delays the form ation tensile cracks around indentations. (C) 1997 Elsevier Science S. A.