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Materials for turbine blades experience in service a combined loading of low and high cycle fatigue at high temperatures. In order to understand the failure behaviour under these loading conditions, systematic investigations were carried out. Low cycle fatigue, high cycle fatigue and combined low and high cycle fatigue tests were realised on MAR-M247 LC at 650 °C in an air environment under total strain control. Surface damage and fracture surfaces were analysed. Under combined low and high cycle fatigue, the lifetime is reduced if the low cycle fatigue leads to a degradation of the high cycle fatigue strength caused by crack initiation and crack growth. By analysing the fracture surface, the crack growth rate under combined cycle fatigue loading could be determined and it was significantly higher than under pure low cycle fatigue loading. The accelerated crack growth mainly causes the lifetime reduction.

Low cycle fatigue (LCF), high cycle fatigue (HCF), and combined LCF and HCF tests are carried out on MAR‐M247 LC at 650 °C in air environment. Under combined LCF and HCF loading, block striations form on the fracture surface which are used to complete an effective crack growth curve by using the linear summation model. Crack growth lives starting from equivalent initial flaw sizes are calculated by the crack closure code FASTRAN and compared with experimental fatigue lives. Under HCF loading, predicted and experimental fatigue lives agree well for lifetimes above 105 cycles. Lower lifetimes are overestimated indicating that the linear summation model is not valid for MAR‐M247 LC in this loading range. Interactions between the non‐crystallographic HCF crack growth and striated crack growth that is caused by the LCF loading are probably responsible for this behavior.

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