Platinum aluminide coating structural effects on hot corrosion resistance at 900 °C

Abstract

Studies have shown that platinum modified aluminide coatings can exhibit a range of structural variations depending on initial platinum thickness, prealuminizing heat treatment, aluminizing cycle, and postcoating heat treatment. It had been speculated earlier that such structural variation could account at least in part for some of the reported variation of performance of these coatings. A series of archetype structures was prepared on IN738 by two aluminizing processes: (i) low aluminum activity and (ii) high aluminum activity; and tested at 900 °C under conditions producing so called Type I high temperature hot corrosion. The results of the present investigation showed that the addition of platinum greatly improved the hot corrosion resistance. It is observed that the low aluminum activity process has better corrosion resistance than that of the high aluminum activity process. It is also found that the surface degradation of both aluminizing processes is quite severe when the specimens were given prolonged prealuminizing diffusion heat treatment. Microstructural observation revealed a significant difference in coating thickness in both the processes and it depends on prealuminizing diffusion and the subsequent aluminizing treatment employed.