Thermal–mechanical fatigue behaviour of CMSX-4 in virgin and long term aged conditions

Abstract

The thermal–mechanical fatigue (TMF) behaviour of the single crystal alloy CMSX-4 has been investigated under out of phase (OP) loading in the 100–1000°C temperature range with a dwell period of 5 min. The material was tested in both virgin and aged conditions. Even though aging at 1000°C for 4000 h seems to have no significant influence on the OP TMF life, a more ductile fracture appearance was generally found for the aged material. This is also illustrated by the difference in the shape of the stabilised stress–strain hysteresis loop between virgin and aged materials, where one can see a higher degree of inelastic deformation for the aged material due to a higher degree of creep relaxation during the dwell period and more plastic deformation in the cold end of the TMF cycle. Microstructure studies showed that rafting occurred in the virgin material even during a short term TMF test with a maximum temperature of 1000°C, which may explain some of the similarities in terms of cyclic life between the two tested material conditions. The rafting was however more pronounced in the aged material where topologically close-packed phases also were found.