Coating application to superalloys provides oxidation and corrosion resistance. One of the key elements in gas turbine coatings is aluminium (Al) which forms a thin, dense alumina layer upon exposure to oxygen and impedes further oxygen diffusion into the alloy. However, Al in the coating depletes due to inward diffusion and oxide formation. The rate of Al depletion is a function of the coating composition/structure, substrate alloy composition/structure and service conditions. In this study, a PtAl diffusion coating, was applied onto polycrystalline IN738LC and single crystal CMSX-4. The coated systems were exposed to 1080°C for 1000 h. Both SEM and XRD analyses were carried out on the as-coated and tested samples. It was found that despite the much higher Al content in CMSX-4, Al depletion was greater. With the higher Cr in IN738LC, a diffusion barrier enriched in Cr/Mo was able to form and reduce the Al depletion.

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Materials at High Temperatures
Department of Mechanical and Aerospace Engineering

Tepylo, N. (Nick), Huang, X, & Yang, Q. (Qi). (2019). Al depletion and elemental redistribution in PtAl coated CMSX-4 and IN738LC after high-temperature exposure. Materials at High Temperatures. doi:10.1080/09603409.2019.1642556