Influence of stress state on the kinetics of γ-channel widening during high temperature and low stress creep of the single crystal superalloy CMSX-4

The present study investigates the kinetics of the widening of gamma-channels in the gamma/'gamma-microstructure of the single crystal superalloy CMSX-4 during high temperature and low stress creep using scanning and transmission electron microscopy (TEM) in combination with quantitative image analysis. gamma-channel widening is an important process because it affects dislocation plasticity in the gamma-channels which is one key element of the overall creep process in single crystal super alloys. We compare the kinetics of rafting in <001>-tension and in vertical bar011vertical bar <01 (1) over bar >-shear creep testing at a constant maximum principal stress sigma(1) =50 MPa at 1080 degreesC. gamma-channel widths follow log-normal-distributions. After subtracting effects due to the change of morphology associated with rafting, the increase of the mean value Of gamma-channel widths is governed by a parabolic rate law and there is no significant difference between uniaxial <001>-tension and vertical bar011vertical bar <01 (1) over bar >-shear creep testing. This suggests that gamma-channel widening is controlled by a multiatom diffusion process through the channels and that for multiaxial loading, the normal stress components perpendicular to the gamma/gamma-interfaces are important. (C) 2001 Elsevier Science B.V. All rights reserved.