The influence of substrate bias on the surface morphology, microstructure and mechanical behaviour of TiNiN coatings

Abstract

The application of a negative substrate bias during physical vapor deposition can have important effects on the surface morphology, structure and properties of ceramic-based coatings. In this study, a number of TiNiN coatings were prepared onto AISI M2 steel substrates via cathodic arc deposition method by employing a range of different negative substrate bias voltages. The objective of this work is to study the influence of bias voltage on the surface morphology, microstructure and mechanical characteristics of these thin films. A change from a fine columnar grained structure to highly refined equiaxed grains was noted with increasing bias from 0 to −50 V, associated with the energetic ion bombardment at the higher substrate bias. A very high hardness value of ∼ 34.2 GPa was attained at a −100 V substrate bias, which was attributed to the synergistic effects of a number of factors such as the presence of compressive residual stresses, solid solution hardening effects along with grain refinement. In addition, significant reduction in the density of microparticle-related defects generated in these coatings was achieved at ≥ -100 V, which can presumably be ascribed to the higher repulsive force induced at higher substrate bias values.