Solid solution hardening in nanolaminate ZrN-TiN coatings with enhanced wear resistance

Abstract

Coating architectures with a microstructure controlled on nanoscale enables the attainment of enhanced mechanical, tribological and other properties. In the present study, we fabricated nanolaminate ZrN/TiN systems with various modulation periods, L, ranging from 1 to 100 nm using pulsed DC magnetron sputtering. It was observed that a modulation period of L = 10 nm is a threshold value for the transition from a periodic to a solid solution structure. We demonstrate that the coatings with L<10 nm displayed a single-phase solid solution with a Zr-rich composition of Ti0.35Zr0.65N. This indicates the effect of mixing and/or diffusion between the two phases that occurred during the film growth. The crystallite size was found to vary with the modulation periodicity: we obtained 11–12.5 nm for the Ti0.35Zr0.65N solid solution, and 14.5–25 nm for the laminate structure. The solid solution and interface strengthening were found to be the main cause of the hardening of the nanolaminate structure presenting a hardness of 32–35 GPa, significantly higher than for the individual TiN (21 GPa) and ZrN (16 GPa) single-layer coatings. The hard, solid solution system was found to exhibit the highest wear resistance corresponding to the highest values of the H/E and H3/E2 ratios related to a high resistance to plastic deformation and a high toughness. Finally, a model for the Ti0.35Zr0.65N solid solution phase formation related to internal residual stress is proposed.