Improving the Adhesion of a Hard Oxide Layer on Ti6Al4V by a Three‐Step Thermal Oxidation Process

Abstract

Thermal oxidation is a promising technique to improve the tribological properties of Ti6Al4V. Herein, a single‐step process consisting of oxidation in air, a two‐step process with an additional solid‐state oxide layer reduction step under vacuum, and a three‐step process with an appended final oxidation step in air are applied to Ti6Al4V. The oxide layer adhesion after the three‐step process is improved compared with the single‐step process. This improved adhesion is not due to a different nature of the oxide layers because oxide layers obtained during the single‐step and three‐step process show a similar morphology and composition. Instead, it is ascribed to the presence of an optimized oxygen diffusion zone with two distinct regions: a gradual decrease in oxygen concentration from the maximum possible oxygen concentration at the oxide–substrate interface until a depth of 20 μm followed by a near‐linear decrease until a depth of about 85 μm. Both regions are also visible in the correlated microhardness‐depth profile.