Microstructure of diffusion aluminide coatings on Ti-base alloy IMI-834 and their cyclic oxidation behaviour at 650 °C

The present study describes the microstructural details of plain pack aluminide and Pt-aluminide coatings on Ti-base alloy IMI-834 and their cyclic oxidation performance at 650 °C in air. While the plain aluminide coating consists of a single layer of Al3Ti phase, the Pt-aluminide coating is constituted of two layers, with the outer layer consisting of PtAl2 and Al3Ti phases and the inner layer of Al3Ti phase. These two coatings display excellent cyclic oxidation resistance on IMI-834 alloy although the Pt-aluminide coating is found to be somewhat superior to its plain aluminide counterpart. Virtually no coating degradation occurs even after 500 h of oxidation exposure at 650 °C. In this study, a layer of pure Pt deposited by electroplating is also found to offer limited protection against oxidation to the above alloy. TiO2 is found as the primary oxide phase in the oxidation of bare IMI-834 alloy.