Tribological properties of nickel-base nanocrystalline coatings sputter-deposited on austenitic stainless steel

Abstract

500 nm-thick films are deposited on austenitic stainless steel by neutral (Ar +) or reactive (N +) ion beam sputtering of Ni or NiTi targets, with (or without) high energy 160 keV-Ar + ion beam assistance. Most of the time the coatings are nanocrystalline and induce a large (excellent in some conditions) increase of the wear resistance. Only Ar + ion beam sputtering of a NiTi target gives an amorphous deposit which does not improve the substrate tribological properties. The hardness and wear resistance of ion beam assisted films are larger than those obtained with non-ion beam assisted coatings. The presence of a hard TiN phase inside a ductile Ni phase, of grains with preferential orientation beneficial to slip, as well as film densification are the main factors which increase the wear resistance. The best results are obtained when the structure is composed of two phases, Ni and TiN. The TiN phase strengthens the already good tribological Ni properties and the Ni ductility induces mechanical accommodation during the friction process.