Substrate Effect on the High-Temperature Oxidation Behavior of a Pt-Modified Aluminide Coating. Part I: Influence of the Initial Chemical Composition of the Coating Surface

Abstract

The effect of substrate composition on the oxidation behavior of the industrial NiPtAl coating RT22 TM was investigated by studying the isothermal and cyclic-oxidation behavior of this coating deposited on three different Ni-base superalloys (CMSX-4 TM , SCB TM and IN792 TM ). Isothermal tests were performed at 900, 1050 and 1150°C for 100 h. Cyclic oxidation was studied at 900°C with a holding time of 300 h for up to 52 cycles (i.e, 15,600 h at 900°C). Thermogravimetric analysis (TGA), X-ray diffraction (XRD), microstructural and analytical investigations using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM), both equipped with energy-dispersive X-ray spectroscopy (EDS) were performed to characterize the oxidation behavior of the systems studied. An effect of the superalloy substrate was observed and related to the initial chemical composition of the coating surface which depends on the superalloy and the associated heat treatments. The effect of the substrate’s alloying elements is discussed. Particularly the influence of Ti and Ta that formed rutile-type oxides inducing oxide-scale cracking and spallation. The excellent resistance to cyclic oxidation of the coating systems studied at 900°C was also demonstrated from very long duration tests of 15,600 h.