Mechanical, tribological and adhesive properties of oxide layers obtained on the surface of the Ti–6Al–7Nb alloy in the thermal oxidation process

Abstract

The mechanical, tribological and adhesive properties of oxide layers obtained on the Ti–6Al–7Nb alloy surface through thermal oxidation at temperatures of 600, 700 and 800 °C for 24 h have been identified in the study. The morphology of the scale formed was determined. It was found that with an increasing oxidation temperature, an increase in the continuity of the oxide scale takes place. The surface covered by oxide layers was characterised by 3 times higher hardness compared to the as-received condition. It was shown that the presence of oxide layers on the surface of Ti–6Al–7Nb alloy led to a significant reduction in wear despite an increase in the value of the friction coefficient. The best sliding wear resistance was found in the oxide layer obtained at a temperature of 700 °C (a 70% reduction in wear). The tribological interaction of ZrO2 balls with the surface of the alloy covered with oxide layers also resulted in a significant reduction in their wear (86% for the oxide layer obtained at 800 °C). It was shown that the wear resistance of ZrO2 balls increased with the oxidation temperature. The values of critical load being the measure of adhesion of the formed scale were determined in scratch-test, which showed that the layer obtained at 700 °C had the best adhesion. The tests showed a relationship between the adhesion of oxide layers and sliding wear resistance. The layer with the best adhesion, which was obtained at 700 °C, was also characterised by the highest resistance to sliding wear.