A temperature-dependent model for predicting the fracture toughness of superalloys at elevated temperature

The plane-strain fracture toughness of tensile mode KIC of superalloys at elevated temperature plays an imperative role in damage tolerance design and structure integrity assessment. In this paper, a novel temperature-dependent model is proposed to predict KIC values of superalloys at elevated temperatures, which is based on stress-strain curves and linear expansion coefficients α of superalloys. Firstly, relation between KIC and strain-hardening exponent n, Young's modulus E is introduced based on Krafft's model. Then, relation between n and temperature is established by a semi-empirical method, and relation between E and temperature is derived based on physical meanings. To validate the model, KIC measurement tests on standard specimens made from turbine disc Nickel-based superalloy GH4720Li are conducted under temperatures of 25 °C, 300 °C, 550 °C, 600 °C, and 650 °C, respectively. Tested results of GH4720Li show that the maximum error between the predicted values of KIC and tested ones is within 10% under all temperatures. Tested KIC results of another superalloy GH4169 (High temperature materials session of China metal institute, 2012) also agree well with the predicted ones of the model. The model can be used to design high temperature components based on damage tolerance design concept.