CYCLIC OXIDATION BEHAVIOUR OF Ir-Ta MODIFIED ALUMINIDE COATINGS ON NICKEL BASE SINGLE CRYSTAL SUPERALLOY

摘要

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. percent 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. percent) in the as aluminized condition, Al content in the Ir-rich base layer is about 60 at. percent and the diffusion zone containing beta-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 gamma'-Ni3Al and topologically close packed phases ahead of the diffusion zone, suggesting the fact that Ir-rich aluminide works as a diffusion barrier distribution of Al after the aluminizing process dominantly affects the microstructure and the oxidation resistance of the modified aluminides and internal microstructural evolution.