Cyclic oxidation behavior of uncoated and aluminum-rich nickel aluminide coated Rene-80 superalloy

In this study, aluminide coating was employed to enhance the high-temperature cyclic oxidation of Rene-80 superalloy at 950ºC. The microstructural aspects and phase constituents of samples were  investigated with scanning electron microscopy (SEM) and x-ray diffraction (XRD) techniques. The result of oxidation tests showed that the weight gain in the uncoated sample was considerably higher than the aluminide coated sample, which indicates the higher rate of oxide formation on the uncoated surface. With the aid of microstructural and XRD analysis, it was confirmed that with the increment of oxidation cycles, the thickness of aluminide coating reduced and the protective β-NiAl phase was converted to alumina scales. According to the EDS results taken from the top coat, it was found that with the increase of oxidation cycles, the content of aluminium in the top layer was drastically decreased and the weight percentage of oxygen was considerably enhanced. Also, in higher oxidation cycles, other protective elements such as Cr and Ti outwardly diffused from the inter-diffusion zone (IDZ) layer which led to reduction in the content of these elements in inner zones of the aluminide coating.