Oxidation behavior of platinum containing γ , γ' and TROPEA superalloy

Overview & Synopsis

Platinum is used to form NiPtAl coatings and improve the oxidation/corrosion resistance of nickel-based superalloys operating under harsh conditions. The addition of 2 wt% (0.6 at%) Pt to the bulk composition of a single crystal nickel-based superalloy (TROPEA) markedly increased the mechanical properties at high temperature. However, the effects of Pt on the oxidation behavior of this new superalloy have never been studied, which is the main goal of this paper. TROPEA and model γ and γ’ single-phase alloys were thus oxidized at 950 ℃ in synthetic air. TROPEA reaches a parabolic regime only after 70 h of exposure. The establishment of an α-Al2O3 protective layer is peculiarly delayed in comparison with the parent CMSX-4 superalloy according to literature. TROPEA forms a multilayer of oxides, including a continuous layer of (TixTa1-x)O2 during the transient period. It appears that Pt promoted the formation of this Ta-rich oxide. The Ta-rich oxide layer may play a role hindering the lowering of the PO2 needed to selectively develop Al2O3 scale or its presence just outlines the difficulty of TROPEA to develop the protective Al2O3 scale in presence of platinum in the substrate. The 0.6 at% of Pt addition thus hampers the formation of a continuous and protective layer of α-Al2O3 scale. In contrast, the model γ and γ’ phases are prompt to develop an adherent and even scale of duplex Cr2O3 + NiCr2O4 and of α-Al2O3 + NiO, respectively, when oxidised at 950 ℃ in air for 100 h.