Thermomechanical Fatigue Tests Development and Life Prediction of a Nickel Base Superalloy

Thermomechanical fatigue (TMF) tests are carried out in order to characterize the behavior of turbine blades and vanes materials: superalloys. These materials suffer high stress levels at very high temperature and to simulate these extreme operation conditions a test-piece is subjected to controlled thermal and mechanical strain waveforms. In this paper, a test procedure is explained, which is unusual due to the fact that the heating system is based on direct resistance method and temperature is controlled by means of a pyrometer. For this purpose, emissivity evolution was studied. The effectiveness of the method, as well as some other important aspects such as alignment and a proper thermal-mechanical strain decoupling are discussed. Finally, some preliminary results of the cyclic behavior and life prediction of C-1023 nickel base superalloy are introduced. This also includes an analysis of specimens fractography.