Effect of thermal oxidation on microstructure and wear resistance of TiZrNb medium-entropy alloy

Abstract

Ti45Zr45Nb10 medium-entropy alloy (TZN MEA) possess superior biomechanical characteristics, characterized by a low modulus of elasticity (55 ± 2 GPa) and high yield strength (678 ± 17 MPa); however, its inferior wear resistance restricts its application in the biomedical field. Surface modification techniques can address this deficiency. Among these techniques, thermal oxidation stands out as a straightforward and environmentally benign technique capable of significantly enhancing the surface attributes of alloys. In the present investigation, TZN MEA was subjected to thermal oxidation treatment across a temperature range of 400 to 500 °C for 2 to 6 h. The impact of oxidation time and temperature on the alloys' morphological, weight, oxide layer thickness, phase composition, hardness, and frictional properties have been examined. With increasing oxidation time and temperature, the oxidation kinetics of the alloys followed a parabolic trend, with the oxide layer thickness on the surface increasing from 0.9 to 13.3 μm and the density rising from 0.647 to 1.097 g·cm^‐3. The oxide layer primarily consisted of TiO₂ and ZrO₂, with a minor contribution from Nb₂O₅. The development of a high-hardness oxide layer and the concurrent increase in density led to a pronounced enhancement in the hardness of the oxidized specimens, which increased by a factor of 1.5 to 4 (377 to 1133 ${\mathrm{HV}}_{0.05}$). Furthermore, their wear resistance was significantly improved, with the wear volume being reduced from 0.0627 mm³ to the range of 0.00023 mm³ to 0.00037 mm³. Comparative analysis with Ti6Al4V alloy revealed that the TZN MEA exhibited superior wear resistance after thermal oxidation. The wear mechanism of the oxidized samples is dominated by abrasive wear. Moreover, the corrosion resistance and wettability after thermal oxidation are improved to a certain extent. These results indicate that the TZN MEA has excellent wear resistance after thermal oxidation, which broadens their application prospects as a human implant.