Cyclic oxidation of Pt/Pd-modified aluminide coating on a nickel-based superalloy at 1150 °C

Abstract

Pt-, Pd-, and Pt/Pd-modified aluminide coatings were prepared on Inconel 738LC by pack aluminizing at 1034 °C. During pack aluminizing, Pt-modified aluminide coating formed a two-phase β-NiAl + PtAl 2 layer and a β-NiAl layer on an interdiffusion zone, whereas Pd- and Pt/Pd-modified aluminide coatings formed only the thicker β-NiAl layer. However, Pd-modified aluminide coating had many pores. During cyclic oxidation, Pt/Pd-modified aluminide coating had a surface that was less rumpled than that of Pt-modified aluminide coating due to its thicker thickness. Pt/Pd-modified aluminide coating had a 22% greater Al-uptake than Pt-modified aluminide coating. Cyclic oxidation tests at 1150 °C showed that Pt/Pd-modified aluminide coating had the best cyclic oxidation resistance. After the cyclic oxidation, an additional γ-Ni phase was seen beneath the outermost alumina scale on the the γ′-Ni 3Al phase in Pt/Pd-modified aluminide coating. The γ-Ni phase, which had a higher Cr content, increased the adhesion and stability of the alumina.