Combinatorial approach to the growth of α-(Al1 − x,Crx)2 + δ(O1 − y,Ny)3 solid solution strengthened thin films by reactive r.f. magnetron sputtering

Abstract

The design and synthesis of Al–Cr–O–N thin films in a metastable solid solution strengthened α-(Al1−x,Crx)2+δ(O1−y,Ny)3 microstructure are described. The deposition experiments were carried out by reactive r.f. magnetron sputtering in an argon–oxygen–nitrogen atmosphere for the sputtering from a segmented target, composed of an Al half plate and a Cr half plate. The constitution, microstructure and Vickers micro hardness of the coatings are discussed in dependence of the deposition parameters and the elemental composition. The range of α-(Al1−x,Crx)2+δ(O1−y,Ny)3 phase formation is shifted to higher Cr/(Al+Cr) ratios with increasing nitrogen gas flow. A γ-Al–Cr–O–N phase is formed at high total gas pressures and low Cr/(Al+Cr) ratios. The solid solution strengthening in the quaternary material system leads to a significant Vickers micro hardness increase compared to α-(Al1−x,Crx)2O3 coatings deposited in the same PVD machine under corresponding process parameters. The α-(Al1−x,Crx)2+δ(O1−y,Ny)3 thin films offer an additional restraint of the lattice by the incorporation of nitrogen and therefore higher Vickers micro hardness values are measured compared to the Al–Cr–O material system.