Duration-affected creep behaviors of Ni-based single crystal superalloys with/without rhenium addition designed for IGT application

Abstract

In this study, the creep behaviors of two Ni-based single crystal superalloys with/without Re addition designed for industrial gas turbine application were investigated at 900 °C under a range of applied stresses (200 MPa–330 MPa), and the examinations of the microstructures and dislocation configurations were performed at the minimum creep rate and creep rupture under each condition of both alloys. The results indicated that although the creep lives spanned over thousands of hours under different stresses, dislocations underwent the similar mechanisms including the proliferation and movements by gliding-climbing process in decelerating stage, followed by the progressive increase in dislocations shearing into the γ′ phases until creep rupture in each alloy. This led to a special rafting regime which was characterized by the sluggish formation of the rafting structure in the present superalloy, considering the relatively lower γ′ volume fraction, lower lattice misfit, and lower elemental diffusion of the experimental superalloys than those of traditional Ni-based superalloys. Thus, the “duration effect” was proposed to describe the strong correlation between the creep duration and microstructural evolution, which showed insensitivity to the applied stress and accumulation strain, resulting in the consistently exponential relationships between the time to the minimum creep rate and the applied stress or creep life of each alloy within a wide range of stresses. The addition of Re gave rise to an inversion of the rafting tendency during high-temperature creep without changing the deformation mechanism under different stresses. Nevertheless, the addition of Re could still enhance the creep property under each stress, which contributes to provide insights for optimizing the alloying design and enhancing long-term reliable service of industrial gas turbine blades.