Structural properties and cyclic oxidation behavior of Ni-Al-Y superalloys

Abstract

The microstructure, microhardness, and oxidation resistance of ternary model Ni-13Al--2Y(at.%) and Ni-11Al-4Y (at.%) superalloys were studied in detail. The microstructures of alloys consisted of primary gamma-Ni dendrites and residual eutectic. The Ni17Y2 intermetallic and gamma-Ni were the major constituents of the eutectic phase mixture. The microhardness value of Ni-11Al-4Y alloy was higher than that of Ni-13Al-2Y alloy because of the higher amount of relatively harder eutectic. With increasing Y concentration from 2 to 4 at.%, the mass gain, oxide scale thickness, and oxidation rate remarkably increased. For both alloys, the oxide scale was comprised of three layers: NiO as a surface layer, Al2O3 as an inner layer in the metal/oxide interface, and mixed Al/Y oxides as an internal layer. Although the studied alloys exhibited fairly good scale adherence in conjunction with almost no important scale spallation, they exhibited faster oxidation kinetics along with higher mass gains.