Cyclic oxidation behaviour of Ir-Ta modified aluminide coatings on nickel base single crystal superalloy

An investigation on microstructure, composition variation and phase distribution in Ir-Ta modified aluminides on Ni-base single crystal superalloy, TMS-75 subjected to cyclic oxidation at 1373K is reported. Ir-Ta coatings with Ta = 14.1, 23.1, 40.7 and 82.9 at.% were deposited on <100> oriented nickel base single crystal superalloy, TMS-75 by DC magnetron sputtering and then subjected to aluminizing and cyclic oxidation. For Ir-rich aluminides (Ta ≤ 40.7 at. %) in the as aluminized condition, Al content in the Ir-rich base layer is about 60 at. % and the diffusion zone containing β-NiAl phase is seen distinctly from the other zones. The mass gain as a function of number of cycles data demonstrates an improved oxidation resistance with decreasing Ta content. In contrary to Ta-rich aluminides, Ir-rich aluminides show the absence of γ'-Ni3Al and topologically close packed phases ahead of the diffusion zone, suggesting the fact that Ir-rich aluminide works as a diffusion barrier, distribut ion of Al after the aluminizing process dominantly affects the microstructure and the oxidation resistance of the modified aluminides, and internal microstructural evolution.