Influence of mechanical properties on the nanoscratch behaviour of hard nanocomposite TiN/Si₃N₄ coatings on Si

A dual ion beam system has been used to produce hard nanocomposite TiN/Si₃N₄ coatings on silicon substrate. Mechanical properties have been determined by nanoindentation and tribological properties have been measured by nanoscratch testing. Nanoindentation showed that harder nanocomposites exhibited higher ratios of hardness to modulus (H/E). The dependence of the resistance to plastic deformation (H³/E ²) on hardness was approximately linear. The H/E value influenced the nanoscratch behaviour. Coatings with higher H/E showed higher critical loads for elastic-plastic transition and also the total coating failure occurring in front of the probe. However, coatings with higher H/E also exhibited an unloading failure, occurring behind the probe at much lower load than the loading failure. Optimizing this stress-related unloading failure could be more important for tribological applications.