Microstructure and creep resistance of a diffusionally aluminized Ni-base superalloy

Abstract

An aluminide layer was formed on a wrought Ni-base superalloy by the diffusional aluminizing method, which involves a physical vapor deposition of Al followed by two-step heat treatment in vacuum. Microstructural analysis revealed the presence of an aluminide layer, inter-diffusion zone (IDZ), and affected substrate, all of which developed due to the inter-diffusion of deposited Al and elements in the matrix. In addition, a wide carbide free zone, in which grain boundaries were mostly denuded of carbides, was found below the IDZ. Depth profiling analysis using a glow discharge spectrometer confirmed the reduced carbon content in the carbide free zone. At 900 A degrees C, the diffusionally aluminized specimens showed a decrease in creep-rupture life caused by the presence of the carbide free zone. Fracture surface and cross-section microstructure observation confirmed the detrimental effect of the carbide free zone on the creep resistance of the diffusionally aluminized Alloy 617