Modelling the structure and mechanical properties of oxide layers obtained on biomedical Ti-6Al-7Nb alloy in the thermal oxidation process

Abstract

The influence of thermal oxidation parameters on oxidation kinetics, morphology, thickness and mechanical properties of oxide layers obtained on biomedical Ti-6Al-7Nb alloy was determined during tests. Thermal oxidation was carried out in varied temperature/time conditions (temperature: 600, 700, 800 °C, time: 6, 24, 48, 72 h). It has been demonstrated that temperature has a more important influence on the oxide scale formation process. It has been found that increasing oxidation temperature from 600 to 800 °C causes a 10-fold increase in mass. Thickness of formed oxide layers changed as oxidation time and temperature increased. Layers obtained at 600 °C had small thickness (up to 0.22 μm). Thicker layers (from 0.32 to 1.05 μm) were obtained after oxidation at 700 °C. Oxidation at 800 °C caused formation of the thickest oxide layers (from 1.56 to 5.42 μm). Thermal oxidation parameters affected hardness of the obtained oxide layers, which increased along with oxidation time and temperature. Higher hardness below the oxide layer has also been observed, which indicates the presence of an intermediate diffusion zone. The tests have shown that thermal oxidation decreases mechanical and plastic properties of Ti-6Al-7Nb alloy.