Influence of Alloy Composition and Exposure Conditions on the Selective Oxidation Behavior of Ni-Al Alloys.

Ni-Al coating alloys, which are commonly used in gas turbine engines operating in marine environments, are highly susceptible to hot corrosion attack. The effect of alloy composition and exposure conditions on the development of a protective alumina scale, which is important for the hot corrosion resistance of the alloy, and how they affect the transition of alumina from the θ to the α polymorph have been evaluated. A series of Ni-Al model alloys with a base composition of Ni-36 at.% Al, and 5 at.% additions of Cr, Pt and Si were exposed in dry air and in air-10%HO at 900 °C. The presence of water vapor in the gas led to higher oxidation rates and retarded the θ- to the α-AlO transformation. The oxidation behavior of the alloys and the alumina polymorph which formed differed depending on the alloying element considered. Additions of Cr accelerated the θ to α transformation, while Pt and Si retarded it. [ABSTRACT FROM AUTHOR]