S. Hamadi, M.-P. Bacos, M. Poulain, S. Zanna, A. Seyeux, V. Maurice, P. Marcus

Turbine blades and vanes in aeronautical engines are protected against the aggression of hot gases by thermal barrier systems. A typical industrial system is made of AM1 nickel-based superalloy coated with a (Ni,Pt)Al intermetallic layer and a yttria partially stabilized zirconia top layer. A current issue is to match the industrial demand for replacing expensive platinum while retaining the good resistance against oxidation provided by the (Ni,Pt)Al coating. An aim of this work is to study the oxidation behavior of a NiAl coating doped with zirconium, well-known for improving the adhesion of thermally grown alumina on top of NiAl bulk materials. A thermochemical vapor phase process was used to codeposit Al and Zr on AM1 to form a Zr-doped NiAl coating. We first showed that AM1/NiAl(Zr) provided better resistance against cyclic oxidation than AM1/(Ni,Pt)Al and AM1/NiAl, when exposed to 1h-cycles at 1100°C. Microstructural and analytical characterizations of the oxidized NiAl(Zr) and NiAl coatings were made at key times to observe the influence of Zr on the evolution of the system. We compared the ageing of the coating (composition, Zr diffusion), the oxide evolution, and the roughness variation of the metal/oxide interface. It appeared that the effects of Zr on long-time oxidation can be explained by the influence of this reactive element during the very first steps of oxidation. The experimental means used for this investigation comprise thermogravimetry, SEM(+EDS), and extreme surface analyses (XPS, ToF-SIMS).

Role of Zirconium

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