Low cycle fatigue behavior of René 80 at elevated temperature

Low cycle fatigue of René 80 was studied at 871 and 982 °C. It was found that when the data were represented on the basis of plastic strain, the life increased with decreasing frequency and imposition of a 90 s hold at maximum strain. Transmission electron microscopy studies showed that the ′ coarsened and an interfacial array of edge dislocations developed. The density of dislocations in the matrix was very low. Light optical microscopy revealed that cracks generally inititiated at oxide spikes in surface connected grain boundaries. A crack initiation criterion based on the maximum stress and oxide depth at the time of crack initiation was found to represent the data very well. Based on that representation, an expression for the initiation fatigue life was developed. That expression includes temperature, frequency and cyclic stress strain parameters as variables. S. Liu, formerly Research Associate at the University of Cincinnati.