The aim of this paper is to investigate different factors, including dwell time, strain range, and strain ratio on creep-fatigue endurances in nickel-based Inconel 718 and GH4169 superalloys. We also summarize classic approaches for life assessments based on the generalizations of Coffin–Manson equation, linear damage summation (LDS), and strain-range partitioning (SRP) method. Each approach does have some degree of success in dealing with a specific set of creep–fatigue data. In order to evaluate the prediction capabilities of the validated approaches, a Bayesian information criterion (BIC) allowing for maximum likelihood and principle of parsimony is used to select the best performing model.

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Investigations into creep-fatigue life and the corresponding failure physical mechanism are crucial for guaranteeing the structural integrity of components.In this work, a series of strain-controlled fatigue and creep-fatigue tests were performed at different temperatures. Then, the EBSD-TEM combinative analysis was performed to reveal the microstructure evolution. The creep failure parameter dependence derived from standard creep experimental data and their importance in further creep-fatigue employment were discussed. Resultsshow that strain energy density has better relevance than ductility in connecting with creep failure. The temperature-dependent critical strain energy density and an equivalent failure strain energy density, considering geometric effect, were incorporated with the current energy-based model, which enables creep-fatigue life scatter within a factor of 1.5. Moreover, multi-slip activations and severe slip interactions under creep-fatigue conditions were responsible for the ultimately lifetime reductions based on microstructure observations.

Damages caused by the effects of cyclic loading (fatigue) and high temperature (creep and oxidation) have been considered critical and need to be appropriately evaluated. A series of strain‐controlled fatigue and creep‐fatigue tests are performed on P92 at 873 K under oxygen‐containing environment. The creep‐fatigue life prediction results are summarized using models based on strain‐range partition, Manson–Coffin equation and linear damage summation (LDS) rule. Obviously, the models based on the LDS rule show relatively good performance with an error band of ±2.5. In view of the adverse effects of oxidation on creep‐fatigue endurance, this paper further develops a physically‐based oxidation damage equation, which is incorporated into LDS rule for the improvement of life assessment. The predicted and experimental results falling into ±1.5 error band proved the accuracy of the proposed oxidation damage equation in the LDS rule. Additionally, model selection criteria are recommended to evaluate the model prediction capabilities.