Residual stresses in nitride hard coatings prepared by magnetron sputtering and arc evaporation

Abstract

Nitride hard coatings such as TiN or (Ti,Al)N produced by magnetron sputtering and arc evaporation processes are characterized by large compressive stresses up to −15 GPa. In the case of magnetron sputtering the highest stress values can be observed at high bias voltages and low substrate temperatures. Coatings produced by arc evaporation, exhibit high compressive stresses even in the case of no bias voltage. The stresses are also influenced by substrate temperatures. In both cases the growing layer is bombarded with accelerated particles. However, there are differences in the kinds of particles. We assume that in the case of sputtering Ar ions and in the case of arc evaporation metal ions with high kinetic energy push nitrogen atoms from regular lattice sites into tetrahedral holes of the rock salt type lattice and occupy the previous nitrogen sites. During arc evaporation the formation of vacancies (Frenkel defects) is also possible. Both effects, the incorporation of argon or metal atoms on nitrogen sites and the nitrogen interstitials, produce high compressive residual stresses. During annealing interstitial nitrogen diffuses to inner boundaries or to the surface. High residual stresses are decreased.