Oxidation behavior and wear resistance of biomedical Ti6Al7Nb alloy

In order to improve the surface wear resistance of the biomedical titanium alloy Ti6Al7Nb, the oxidation behavior was studied in air at 500-800°C for 2-12 h and then its improved wear resistance was tested at room temperature. The testing results indicated that the oxidation rate is low at 500-600°C, and the oxidized surface hardness changes little in comparison with the hardness of the alloy matrix. When the temperature exceeds 750°C, the oxidation rate increases and the oxidation kinetics follows the parabolic rule. The oxides mainly consists of compact TiO₂ with small amount of Al₂O₃. At 800°C the oxide particles grow rapidly, thus resulting in a loosened oxidized layer where the spalling effect frequently happens. Taking account of both the depth of hardened layer and oxidizing time, the optimum oxidization parameters are determined to be 750°C/8 h. By such an oxidization schedule, the surface hardness comes up to 1047 HV, especially the wear resistance is greater than 280 times that of original material. The mechanism of wear resistance improvement after oxidation is analyzed in detail.