Microstructural response of mono- and multilayer hard coatings during indentation microhardness testing

An investigation of indentation crack patterns and the nature of fracture mechanisms of hard coatings can provide useful information to aid in the understanding of failure mechanisms occurring as a result of scratch and wear tests. Examples of several different types of single and multilayer coating systems are presented in this study. The effect of substrate and microstructure on the brittle-ductile transition behaviour 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 dissipate a proportion of the energy, then the premature adhesive failure due to the non-compliance of the strain at hard coating/substrate interface can be avoided. The compaction or plastic flow of the hard coating also effectively disperses concentrated stress and delays the formation tensile cracks around indentations.