Wear characteristics of a thermally oxidized and vacuum diffusion heat treated coating on Ti-6Al-4V alloy

In order to improve its poor tribological performance, an oxidation/diffusion coating on Ti-6Al-4V alloy was prepared by thermal oxidation and subsequent vacuum diffusion. The wear characteristics of the coating were explored on a pin-on-disc high temperature wear tester under 50-300 N at 25-600 °C. The oxidation/diffusion coating with a thickness of 250 μm was composed of TiO2, Ti2O and Ti2.5O3 and strongly bonded with substrate because of diffusion. The hardness distribution from the outmost coating to the substrate presented a gradient high-to-low variation; the hardness of the outmost coating reached 820-830 HV. The oxidation/diffusion coating represented extremely low wear losses under various conditions, especially at high loads and temperatures. The wear resistance of Ti-6Al-4V alloy was remarkably improved by the thermal oxidation and subsequent vacuum diffusion. Excellent wear resistance of the oxidation/diffusion coating was mainly attributed to the hard ceramic coating and the strong bond resulted from the thermal diffusion. However, at 600 °C and 300 N, the oxidation/diffusion coating started to present a failure tendency. In this case, the low wear losses seemed to result from the protective tribo-oxide layer. A predominant wear mechanism was suggested to be fatigue wear and transfer.