A study of creep-fatigue interaction in the nickel-base superalloy 263

Ni-based superalloys, such as alloy 263, have excellent creep strength at high temperatures due to precipitation of gamma prime. Therefore they are candidate materials for thick section components as well as tubing in advanced ultra-supercritical (A-USC) power plants where temperatures exceed 700 °C. Because of the lower thermal expansion coefficient the Ni-based superalloys are less prone to thermal fatigue damage than the austenitic stainless steels. A series of creep-fatigue (CF) and low cycle fatigue (LCF) tests have been performed in order to study the effect of the test temperature, hold time, total strain range and a pre-creep exposure of 178MPa / 3000h / 750ºC on the creep-fatigue life of alloy 263. All LCF and CF tests were per-formed using the high precision pneumatic loading system (HIPS) at temperatures in the range of 700-750ºC, the total strain range between 0.5-1.0% and with hold periods up to 10h in both tension and compression. In this paper stress relaxation time plots, ?-N plots and ??-N plots are presented for alloy 263. The creep-fatigue test results are analysed using time fraction ap-proach utilized in the nuclear material assessment and design codes, such as RCC-MRx and ASME III NH. The results are compared against public domain data and fitted to the recently developed ? -model. The ? -model utilizes the creep rupture strength and tensile strength for predicting CF life with a minimum amount of fitting parameters. It is shown that the number of cycles to failure for CF data for alloy 263 can be accurately predicted by the ? -model. Furthermore, the practicality in using the time fraction approach for presenting the combined CF damage is discussed and recommendations for alternative approaches are mad