Thermo-mechanical and low cycle fatigue behaviour of a nickel-base superalloy at elevated temperatures

Abstract

Isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) tests were performed to investigate the deformation behaviour and fatigue life of the nickel-base Superalloy René 80 at elevated temperatures. The LCF test temperature was 950 °C. The TMF tests were performed in the temperature ranges 100–950 °C and 750–950 °C and both out-of-phase (OP) and in-phase (IP) shifts of mechanical and thermal loading. All LCF and TMF tests were conducted with a mechanical strain ratio Rε,me = −1, which allows using the mechanical strain range to compare the material behaviour under LCF and TMF stresses. With respect to the mechanical strain range, the material showed the shortest lifetime under TMF conditions for broad temperature ranges, whereas the TMF tests with narrow temperature ranges resulted in similar lifetimes to those in the LCF tests. Additionally, damage parameters were applied to assess the mean stress development during cycling and the different maximum stresses during IP and OP TMF testing. The Smith–Watson–Topper damage parameter is proposed for the assessment of fatigue life prediction because this parameter provides reasonable trends over the entire lifetime. Nevertheless, LCF and TMF cannot be combined in a single model.