Investigation of Thermal Gradient Mechanical Fatigue Test Methods for Nickel-based Superalloys

Abstract

Background Temperature gradients significantly affect the material fatigue process. A reliable and robust test procedure is needed for quantifying the effects of temperature gradients on the evolution of fatigue damage in nickel-based superalloys. Objective The present study aims to develop a radiation heating system for universal material testing machine for simulating thermal gradient mechanical fatigue in turbines. Methods The developed heating system mainly consists of halogen lamps, reflectors, cooling subsystems, and control units. Based on extensive experimental and computational investigations, a thermal model is developed for accurate thermo-mechanical fatigue testing under given temperature gradients in the heating system, and it is applied to variable temperature fatigue tests. The detail procedure for determining heat transfer coefficients is presented based on experimental and computational results. Results TGMF tests are successfully performed with the developed radiation heating system. The temperature gradients are found to reduce the TGMF life significantly in comparison to that of the TMF life. Conclusions It is confirmed that the developed thermal gradient mechanical fatigue methodology can be applied to different thermo-mechanical fatigue tests with various temperature gradients.