Comparison on the structural, mechanical and tribological properties of TiAlN coatings deposited by HiPIMS and Cathodic Arc Evaporation

Abstract

TiAlN single layer coatings deposited by High-Power Impulse Magnetron Sputtering (HiPIMS) on carbide and Si-wafers substrates were performed. They were characterized in order to study the effects of different process parameters on the film stoichiometry, microstructure and morphology and finally their mechanical and tribological properties were investigated. For comparison, the properties of the same composition Ti50Al50N coatings produced by Cathodic Arc Evaporation (CAE) were also studied. Only the most influential process parameters, which are the effects of duty cycle, pressure, power and bias for the HiPIMS process are here discussed. High-resolution TEM images were used to investigate the microstructure of CAE and HiPIMS coatings and the observations indicate that both processes produced high density Ti50Al50N coatings with a fine fibrous structure, and a similar grain size. XRD analyses showed that TiAlN coatings deposited by CAE and by HiPIMS have a single-phase cubic structure with respectively the (200) and (111) reflection peaks as a preferred orientation. Furthermore, the residual stresses determined by XRD for the HiPIMS coated samples show that it can be possible to tune them from tensile (+500 MPa) to high compressive stresses (−4000 MPa) by adjusting the process parameters. Independently of their intrinsic stress level, the HiPIMS coatings show similar hardness and the values obtained are in the same range of CAE coatings (30–35 GPa) with same composition and thickness. However, during ball-on-disc tests in dry condition using a steel ball against the coated carbide substrate, the behaviour of similar Ti50Al50N as deposited coatings produced by these two processes was different. Lower friction coefficients (−30%) but, higher abrasion kinetic of the steel ball as counterpart during pin-on-disk test (+50%) were recorded for the Ti50Al50N HiPIMS coatings. In conclusion, it is proposed that, for HiPIMS coatings with high compressive stresses (<−5000 MPa), having also low surface roughness and (111) main texture orientation, high tribological properties can be achieved.