The degradation of (Ni,Pd)Al coatings on superalloy IN738 during isothermal oxidation

Isothermal oxidation of the plain and palladium modified aluminide coatings, developed by the low-pressure pack cementation process, on the nickel-base superalloy IN738, has been carried out at 900∼1100 °C, with the primary objective of systematically understanding the coating degradation process during oxidation, by XRD, optical microscopy (OM) and energy dispersive X-ray spectrometry (EDS). Results show that the degradation mechanism of the (Ni,Pd)Al coating is similar to the plain NiAl coating. The microstructural degradation of both the (Ni,Pd)Al coating and NiAl coatings occurs due to phase transformation from β to γ′ during oxidation at high temperature. Palladium may play a significant role in stabilizing the β phase, retarding the degradation of coating, and increasing the coating performance for high temperature oxidation resistance.