Structure and mechanical properties of (Ti,Al)(B,N) coatings fabricated by reactive DC magnetron sputtering

Abstract

We report on a study of structure, composition and mechanical properties of (Ti,Al)(B,N) coatings, deposited by reactive DC magnetron sputtering on Corning glass and AISI D2 tool steel substrates and their dependence on variations of nitrogen/argon flux ratio. The Ti–Al–BN target used was fabricated from a mixture of powders of Ti (70wt%), Al (15wt%) and BN (15wt%). The samples were found in the centre of the ternary diagram of phases of the Ti(Al)–B–N system as a mixture of Ti1−xAlxN, BN and TiB2 phases. BN and TiB2 appear as amorphous materials, while Ti1−xAlxN is a nanocrystalline material with a structure of rock-salt- or wurtzite-type, depending on Al content. We found that the mechanical properties of the coatings are remarkably affected by the structure of the Ti1−xAlxN phase, which is a cubic phase (fcc) for x⩽0.5 and a mixer of cubic and hexagonal (wurtzite-type) for x>0.5.