Thermal treatment effect on the surface and in vitro corrosion characteristics of arc deposited TiN coating on Ti alloy for orthopedic applications

The influence of post thermal treatment at (500,600,700, and 800 degrees C) of cathodic arc physical vapor deposited TiN coated Ti6Al4V (Ti64) alloy was studied for orthopedic uses. The structure, surface characteristics, mechanical properties of coated and treated samples was investigated using XRD, FESEM/EDX, XPS, AFM, and micro indentation. The influence of post heat treatment on the in vitro corrosion-resistant behavior in a physiological medium was assessed by linear polarization, electrochemical frequency modulation, and impedance spectroscopic measurements. The results showed that a TiN layer of 5 +/- 0.15 mu m was formed over Ti64 alloy with higher microhardness and modulus compared to the bare substrate. The rutile TiO2 oxide phase begins to form with the TiN at 500 degrees C, the TiO2 phase intensity increased with the temperature, and the TiO2 upper layer over the TiN film was formed at 700 and 800 degrees C. The microhardness and modulus were increased at 500 degrees C due to enhanced crystallinity of TiN, then decreased with increasing the temperature due to the internal stress relaxation of TiN and formation of the TiO2 phase. The treated samples showed higher resistance to plastic deformation compared to the TiN coated and uncoated alloy. The sample treated at 500 degrees C showed the highest hardness, modulus, and resistance to plastic deformation. The obtained in vitro corrosion results indicated that post thermal treatment improves the corrosion resistance of TiN coated.