Tribological and corrosion behavior of friction stir processed Ti-CaP nanocomposites in simulated body fluid solution

In the present study, friction stir processing was utilized to incorporate nano-hydroxyapatite particles into Ti-6Al-4V substrates to fabricate Ti-CaP nanocomposite surface layer. Microstructures of the stir zone and the fabricated Ti-CaP nanocomposite layer were analyzed using optical and scanning electron microscopy, respectively. Microhardness profile and AFM analysis of substrates were then studied. The microhardness of Ti-CaP nanocomposite layer was reached about 386 HV due to the grain refinement and the distribution of nano-hydroxyapatite particles. Potentiodynamic polarization studies showed that the Ti-CaP nanocomposite layer protected effectively the Ti-6Al-4V substrates from corroding in simulated body fluid solution. The tribological properties of the samples were studied in both dry and simulated biological conditions. The wear rate and friction coefficient decreased by friction stir processing on Ti-6Al-4V substrates. From the analysis of plotted graphs of weight loss versus sliding distance, a correlation between wear coefficient and microhardness through thickness was established. The wear mechanisms were also investigated through scanning electron microscopy. It was shown that the major mechanism was abrasive wear.