الفهرس 
The effect of heat treatment on mechanical and electrochemical behavior of novel near-beta ti alloy for biomedical applications
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Abstract
The present study investigates the microstructural, mechanical and corrosion properties of Ti-7Mo-8Nb alloy manufactured through powder metallurgy and the effects of heat treatments on these properties. The performance of the developed alloy is benchmarked against cast Ti-6Al-4V. Microstructure examination of Ti-7Mo-8Nb revealed a Widmanstätten structure containing equiaxed β grains along with acicular α phase. In regards to the mechanical properties, Ti-7Mo-8Nb possessed higher compressive yield strength, higher hardness but lower elastic modulus than Ti-6Al-4V. The elastic modulus of As Sintered Ti-7Mo-8Nb was almost 44.9 GPa, approaching the usually desired value of 30 GPa for cortical bone. Wear test revealed that the lowest wear rate of Ti-7Mo-8Nb was obtained for the aged sample at 500 ̊C after solution treatment. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments were carried out for As Sintered Ti-7Mo-8Nb, heat treated Ti-7Mo-8Nb and Ti-6Al-4V immersed in Hank’s solution as a simulated body fluid at a temperature of 37°C. Both experiments revealed that the highest corrosion resistance was obtained for the Ti-7Mo-8Nb sample aged at 500 ̊C after solution treatment manifested by lowest corrosion and passivation current densities, highest negative phase angle, highest impedance modulus and largest Nyquist semicircle diameter as compared to other heat treated Ti-7Mo-8Nb and Ti-6Al-4V alloy. Also all heat treated Ti-7Mo-8Nb had corrosion resistance better than Ti-6Al-4V alloy. The superior corrosion properties of Ti-7Mo-8Nb are indicative of the development of a more stable passive layer on the surface. The fitting of EIS data into an equivalent circuit suggested the formation of a double oxide layer consisting of an inner compact base passive film along with an external layer. The presented combination of high strength, high corrosion resistance along with low elastic modulus puts forward the Ti-7Mo-8Nb alloy as a good candidate for orthopedic biomedical applications and among the heat-treated Ti-7Mo-8Nb alloys, Ti-7Mo-8Nb aged at 500 ̊C after solution treatment had the best mechanical and electrochemical properties.