Improvement of Ti alloy fatigue properties by Pt ion plating

The effect of Pt ion plating on the high cycle axial fatigue life of Ti-6Al-2Sn-4Zr-2Mo specimens was studied at room temperature and 455 °C. Unlike other coatings, the plated material tested in this work showed an increase in fatigue strength when compared to uncoated material. The fatigue strength improvement was greater at 455 °C than at room temperature. Coated specimens cycled close to the fatigue limit at 455 °C demonstrated the highest improvement, which was associated with subsurface fatigue crack initiation. The uncoated specimens, tested under similar conditions, failed by cracking at the surface. Sectioning analysis showed no defects in the subsurface initiation sites. The initiation was related to groups of similarly aligned coarse α platelets. It is suggested that the Pt ion plating caused some surface hardening as well as oxidation resistance at elevated temperatures leading to the suppression of surface crack initiation.