Effect of Ni content on the microstructure and mechanical properties of TiNiN coatings

Abstract

Incorporation of Ni can have intriguing effects on the phase composition, microstructure and mechanical characteristics of titanium nitride coatings synthesised by physical vapour deposition. In this investigation, a series of TiNiN coatings, with varying Ni contents, were deposited onto Si substrates using the filtered vacuum cathodic arc method by changing the composition of the TiNi alloy target. The aim of this study is to investigate the effect of Ni concentration (as controlled by composition of the target material) on the phase composition, microstructure and mechanical behaviour of these TiNiN coatings. A transition from a fine columnar structure, at low Ni contents (∼2 at.%), to a much finer equiaxed structure at higher Ni concentrations (≥4 at.%) was noted. A maximum hardness value of ∼ 32.4 GPa was attained in the coating containing a Ni concentration of ∼ 4 at.%, which was ascribed to the synergistic effects of solid solution hardening, grain refinement and the presence of a high compressive residual stress. In addition, the density of macroparticles generated in these TiNiN coatings during arc deposition was shown to be inversely related to the melting temperature of the target material.