Comparison of prediction methods for low-cycle fatigue life of HIP superalloys at elevated temperatures for turbopump reliability

Turbopumps which pressurize fuels and oxidizers are generally used to operate liquid rocket engine for space launch vehicles. It is considered very important to predict fatigue properties at elevated temperatures for the design and manufacturing of reliable turbopump systems. Hot isostatic pressing (HIP) is one of the most promising manufacturing methods for gas turbine rotors. In this research, five kinds of Ni-based superalloys (Inconel 718 HIP, Inconel 718 HIP and heat treated, MAR-M-247 HIP, MAR-M-247 HIP and heat treated and Rene 95 HIP) were investigated at elevated temperatures. Original universal slopes method, modified universal slopes method, Mitchell's method, Bäumel and Seeger's method, and Ong's method have been used for predicting the high temperature low-cycle fatigue performance. Among these methods, Mitchell's method showed the best adaptation results for the life prediction of Ni-based HIP superalloys. A novel equation was suggested by modification of Mitchell's method to predict Ni-based HIP superalloys at elevated temperature more accurately. The equation predicted well the low-cycle fatigue of HIP superalloys as well as of cast Rene 80 at elevated temperatures.