Low cycle fatigue behavior and fracture mechanism of a directionally solidified CM247 LC superalloy

Abstract

In gas turbines, superalloys are exposed to thermal as well as mechanical cyclic loadings during start-up and shut down processes, which can accelerate the formation of fatigue failure mechanisms. In the present study, low cycle fatigue behavior and fracture mechanism of a directionally-solidified CM247 LC superalloy at two temperatures of 600°C and 800°C were investigated. For this purpose, strain-controlled low cycle fatigue tests were carried out at 600°C and 800°C, and constant total strain amplitudes of 0.4, 0.6, 0.8, and 1% were applied during the totally reversed loading ratio (R = -1). The Coffin-Manson model, based on plastic deformation and a model based on the hysteresis energy criterion is used to predict fatigue life and evaluate the low cycle fatigue behavior. SEM observations of the surface of the failed specimen showed similar LCF failure mechanisms in all the strain amplitudes and temperatures.