Fatigue behavior and life predictions of thermally oxidized Ti6Al4V alloy according to oxidation parameters

Abstract

Thermal oxidation is a surface treatment thought to improve the wear behavior of Ti alloys. However, oxidation can impact adversely the fatigue behavior of the alloys. Thermal oxidation of the Ti-6Al-4V alloy was performed under uncontrolled furnace atmosphere, at 600 °C, for 5 h and 10 h, and at 700 °C, for 15 h. Microstructure analysis was performed and no significant changes were observed in the microstructure of the oxidized alloys, except for the diffusion zone formation. XRD analysis denoted rutile peaks (TiO2) in the oxidized alloys. Roughness increased due to oxidation time and temperature, whereas layer thickness was influenced mainly by temperature. The influence of oxidation parameters on fatigue behavior was tested and fracture micromechanisms were analyzed. Fatigue endurance limit after oxidation at 600 °C, for 5 and 10 h; and at 700 °C, for 15 h decreased by 27%, 29% and 68%, respectively, in comparison to the untreated alloy. Premature cracks in the oxide layer encouraged fatigue nucleation, and the premature crack formation explains the diminished fatigue performance of the oxidized alloys. Fatigue endurance limit was assessed through the Murakami’s model, and a fatigue life model was established, which agree with the experimental results.