High temperature fatigue tests on small-scale specimens extracted from high pressure turbine blades for calibrating an efficient lifetime model

Kurzfassung

Small scale low cycle fatigue (LCF) experiments were performed in a temperature range between 20 °C and 950 °C for calibrating a beforehand developed lifetime assessment model, which is based on fracture strength data of the used alloy René 5 combined with LCF data reported in the literature for the well described reference alloy CMSX®-4. Test samples were extracted from high pressure turbine blades to capture the influence of the microstructure, which developed during solidification of thin walled blade structures. To keep the costs within reasonable limits, small-scale samples were extracted from the cooling channel walls of used turbine blades, which have a microstructure close to the pristine state, since they were exposed to moderate temperatures. All fracture surfaces were examined with respect to the origin of lifetime limiting fatigue cracks. Main results of this study were (1) the predictive power of the lifetime model is not sufficient if based on LCF data from reference material, (2) if calibrated with LCF data from the actual material, the model fits well for all temperatures, (3) the observed lifetime scatter discourages extrapolating the model to longer lifetimes, and (4) the lifetime scatter is mainly related to the size distribution of solidification pores.