Influence of applied stress on the γ′ directional coarsening in a single crystal superalloy

It was found in a commercial single crystal superalloy CMSX-4 that preferential orientation of the γ′ rafting in dendrite core was not dependent on the sign of the applied stress σ_A, but on the sign of the sum of the applied stress σ_A and a critical equivalent stress σ_c. This critical equivalent stress σ_c caused by material inhomogeneity has been predicted previously; however it was first determined experimentally to be in the range 39.8–47.2 MPa in the present study. Moreover, it qualitatively demonstrated that the critical equivalent stress σ_c played a significant role in the creep behavior of superalloys at high temperature and low stress.