High temperature tribological behavior of microarc oxidation film on Ti-39Nb-6Zr alloy

The TiO2-Nb2O5-ZrO2 composite film on Ti-39Nb-6Zr alloy was in-situ synthesized by microarc oxidation (MAO) process in potassium hydroxide electrolyte. Morphology, composition and hardness of MAO film were characterized. The tribological behavior of bare and coated Ti-39Nb-6Zr alloy under dry sliding against ZrO2 ceramic ball were studied by a ball-on-disk friction tester at the ambient temperature, 200 °C and 400 °C. Their friction coefficient and wear rate were obtained and wear mechanism analyzed. The MAO surface treatment significantly decreased friction coefficient and wear rate of Ti-39Nb-6Zr alloy at the ambient temperature and 200 °C, but the friction coefficient showed a periodical fluctuation at 400 °C while the wear rate clearly decreased. The MAO film has excellent wear resistance at different temperatures due to the formation of TiO2, Nb2O5, and ZrO2 ceramic phases. The wear mechanism of Ti-39Nb-6Zr alloy was mainly the abrasive wear at ambient temperature, but was transformed to abrasive, adhesive and oxidation wear at high temperature. The MAO treated alloy mainly displayed the adhesive wear at ambient temperature, 200 °C and 400 °C. Furthermore, the polished treatment for MAO film could obviously reduce its low friction coefficient and wear rate at the ambient temperature and 200 °C.