Tailoring the scratch adhesion strength and wear performance of TiNiN nanocomposite coatings by optimising substrate bias voltage during cathodic arc evaporation

Abstract

The tribological properties of TiN-based coatings can be substantially influenced by the choice of substrate bias employed during physical vapor deposition. However, the effects of applied substrate bias voltages during cathodic arc evaporation on to the scratch adhesion strength and wear resistance of TiNiN coatings have not been previously studied. In this present work, a series of TiNiN coatings were fabricated onto tool steel (M2) substrates using the cathodic arc evaporation method by applying a range of bias voltages to the substrate. The aim of this study is to investigate the scratch response and wear performance of these coatings along with an investigation of the deformation mechanisms in operation during scratch and wear tests. The best scratch adhesion strength (i.e., greater LC1, LC2 and CPRs values) was noted for the coating prepared at a bias voltage of −100 V, which was ascribed to the synergistic responses arising from superior mechanical properties, the influence of a high compressive residual stress and a fine, equiaxed nanocomposite structure, that acted to promote effective resistance against cohesive and adhesive failure. Further, the failure mechanisms under progressive loading conditions were also investigated through observation of the complex crack patterns generated, compressive residual stress values and the coatings' hierarchical design. An approximately 85 % enhancement in wear resistance for these TiNiN coatings was achieved as the bias voltage was increased from 0 V to −100 V. This −100 V coating exhibited the highest values of H/Er (>0.1) and We (>60 %), as well as the highest Ni concentration (~ 4 at.%).