Effects of bias voltage on the microstructure and mechanical properties of (Ti,Al,Cr)N hard films with N-gradient distributions

(Ti,Al,Cr)N hard reactive films were deposited on high speed steel substrates by multi-arc ion plating (MAIP) technology using pure Cr and Ti–50Al(at.%) alloy targets. The partial pressure of N2 was raised step by step in each deposition process. The surface morphology, the cross-sectional morphology of fracture sample, the surface compositions and the phase structure of the (Ti,Al,Cr)N films were investigated by scanning electronic microscope (SEM) and X-ray diffraction (XRD). The dense columnar microstructure was obtained in all of the (Ti,Al,Cr)N films, though micro-droplets evidently existed on the surface of the films. The micro-hardness of the film surface, the adhesive strength of the film/substrate and the thermal shock resistance were investigated. The results revealed the effects of bias voltage on the composition, phase structure, and mechanical properties. The improved balanced properties of a micro-hardness of about 50 GPa, an adhesive strength larger than 200 N and a thermal shock resistance of 7–8 cycles were reached at a bias voltage of 150 V. The present super-hard (Ti,Al,Cr)N films with N-gradient distribution may be an actual substitution of TiN, (Ti,Al)N, (Ti,Cr)N and single-layer (Ti,Al,Cr)N hard films.