Tribo-mechanical and electrochemical properties of plasma nitriding titanium

Titanium nitrides have good tribo-mechanical and biomedical properties. They are employed to harden and protect cutting and sliding surfaces for industrial purpose and as a non-toxic outer-surface for bio-medical applications. In this study, pure titanium was nitrided using RF plasma technique. The microstructural, mechanical, tribological, electrochemical and biomedical properties of nitrided titanium were investigated. The X-ray diffraction demonstrates the formation of ε-Ti2N and the cubic δ-TiN phases after plasma nitriding. The microhardness of the nitride samples increases as the plasma-processing power increases up to 1300 HV0.1. That represents approximately 7-fold increment in the microhardness in comparison with the untreated titanium. High nitriding rate of 0.17 μm2/s was recorded for the sample that was treated at 650 W. The wear and corrosion resistance are improved after plasma nitriding. Moreover, the friction coefficient is reduced from nearly 0.75 for the untreated titanium to 0.25 for the nitride one. An enhancement in the biocompatibility of the nitrided titanium has been achieved. The number of grown mesenchymal stem cells was higher for nitrided substrates compared to that of the untreated titanium. The improved tribo-mechanical and electrochemical performance of the nitrided titanium can be attributed to the formation of super-hard titanium nitrided phases.