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Oxidation and creep behaviour of the CVD aluminized Rene 77 nickel-based superalloy

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Turbine blades are heavy loaded elements of the aircraft gas turbines. They are subjected to extremely high mechanical and thermal loads in the chemically aggressive environment. The most important criteria for selection of the blades material are high tensile strength at elevated temperature both for static and dynamic loads, high fatigue and creep strength along with good resistance to high temperature corrosion [1, 2]. Required high temperature oxidation resistance of the modern gas turbine elements can be obtained by application of protective coatings. The most effective and widely used are diffusion coatings containing aluminium: Al-Si, Al-Cr, Al-Pt, Pt‑AlCr and others [3÷6]. Widely accepted techniques of obtaining coatings based on intermetallic phases of the Ni-Al system are pack cementation and out of pack methods. Although they fulfil technological requirements for manufacturing of aircraft engines elements, they present threat to environment because of emission of gaseous chlorides during the process [4]. Aluminizing by chemical vapour deposition method, in which reactive atmosphere is generated in external reactor and supplied in the form of aluminium halides into the main reactor, was introduced successfully to produce heat-resisting diffusion layers of the analogous chemical and phase composition like in traditional methods [4, 7]. This method allows to avoid contact between substrate material and powder mixture and provides more precise control of process parameters. The highest chemical cleanness of the coating obtained by low-activity CVD process additionally increases their oxidation resistance [8, 9]. CVD method allows to form the coating both on the external surface of the turbine blade and simultaneously on the internal surface of the cooling channels having small cross-section. Additionally it enables control of the cooling rate of substrate from process temperature. It facilitates complex heat trea[...]

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