Fabrication and its characteristics of hard coating Ti-Al-N system prepared by DC magnetron sputtering

Abstract

Pseudobinary Ti1−xAlxN films were synthesized on Si (100) wafer by DC magnetron sputtering method using Ti1−xAlx alloy targets with different Al contents. The composition of the Ti1−xAlxN films was determined by electron probe microanalysis (EPMA). Structural characteristic was performed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). First principles virtual crystal calculations for the Ti1−xAlxN disordered alloys were used for the XRD simulations. The crystalline structure of the Ti0.61Al0.39N film was found to be a metastable single phase with NaCl (B1) structure. Its lattice constant, determined by XRD, was less than that of pure TiN. With the increase of Al content, the lattice constant of B1 phase was continually decreased, while wurtzite (B4) structure was observed in the Ti0.40Al0.60N film. When x reached 0.75, the B1 phase disappeared, and only B4 phase was remained. The critical Al content for the phase transition from NaCl to wurtzite structure in this paper was about 0.60, which could be explained by both the thermodynamic model and the electron theory. As-deposited Ti1−xAlxN films exhibited excellent mechanical properties. Hardness measurements of Ti1−xAlxN films showed a high value of 45GPa for x=0.39 and was decreased to value of 27 GPa with increasing Al at x=0.60.