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.

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID : 2962 Abstract. Oxidation kinetics of platinum modified aluminide and overlay coatings on nickel base superalloys were investigated. Isothermal oxidation tests were carried out at 1050°C in synthetic air. Cyclic oxidation tests were performed with 2 cycle frequencies : -Short term cycles : 1h dwells at 1050°C in synthetic air ×1800 cycles -Long term cycles : 300h dwells at 1050°C in laboratory air × 6 cycles (experiment planned to totalize at least 10 000 hours at high temperature) The mass gain curves point out a large effect of the cycle frequency at 1050°C for overlay NiCoCrAlYTa coating whereas the effect is less significant for Pt-modified nickel aluminide coating. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy was used to evaluate the effect of cycle frequency on microstructural evolution. A simple statistical spalling model [1,2], assuming that the parabolic rate constant k p and the spalling probability p are constant, is tentatively applied and discussed in view of the microstructural evolution complexity.

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