Synthesis and annealing effects on the properties of nanostructured Ti-Al-V-N coatings deposited by plasma enhanced magnetron sputtering

In the present study, Ti-Al-V-N coatings were synthesized onto Ti-6Al-4V substrates by plasma enhanced magnetron sputtering (PEMS) of two commercial sputter targets of Ti-6Al-4V in an Ar/N2 gas mixture. After that, the as-synthesized coatings were annealed in air atmosphere at temperature ranging from 500 °C to 900 °C. The as-synthesized and annealed coatings were characterized by X-ray diffraction, Vickers microhardness tester, ball-on-disk tribometer and potentiodynamic polarization tests. The as-synthesized coatings showed a surface hardness of about 2980 ± 80 HV0.3 and a friction coefficient of 0.36. It has been revealed with the increase of annealing temperature; the microhardness was gradually decreased and reached a minimum value of 1030 ± 30 HV0.3 at 900 °C. The coefficient of friction has a minimum value of 0.27 for coatings annealed at 600 °C. Potentiodynamic polarization test confirmed that thermally annealed samples (≤600 °C) exhibit a better corrosion performance compared to that of the as-synthesized one. However, at relatively higher annealing temperature (700-900 °C), a small degradation in the corrosion performance was observed with the formation of oxidized phases. Finally, the variation in the mechanical and tribological properties of this coating with annealing temperatures is attributed to changes in microstructure and chemical nature of the surface layer.