Influence of oxidation on near-surface γ′ fraction and resulting creep behaviour of single crystal Ni-base superalloy M247LC SX

Creep experiments were carried out at 980 °C in vacuum to determine the influence of the varying γ′ fraction on secondary creep. The dependence of stress level on creep rate was approximated by a Norton creep law. The stress exponent n plotted against the γ′ fraction shows a S-shaped behaviour almost doubling at 50% volume fraction. This behaviour suggests a change in the dominant creep mechanism. Using precipitate hardening theories this progression can be attributed to the transition of dislocation movement from cutting ordered γ′ precipitates to Orowan bowing mechanism with decreasing γ′ fraction. These results enable a correlation of oxidation-affected γ′ fraction and secondary creep, which is essential for the design and the improved prediction of creep deformation of thin sections of single crystal turbine blades.