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.

Thermo-mechanical fatigue tests were carried out in MarM-247 nickel-based superalloy with a system that uses the direct resistance method for heating, instead of the common induction system. Therefore, this paper has two aims: (1) to validate the test facility via an inter-comparison exercise (carried out at BAM) and (2) to give an overview of the material behaviour based on cyclic response, lifetime and some microstructural aspects. In-phase (IP), out-of-phase (OP) and in-phase test with 2 minutes of dwell period (IP dwell) were executed. Ostergren and Zamrik life prediction approaches were found to be suitable tools for life assessment regardless of the test-type. In fact, some modifications in the mentioned models allow predicting life within a factor of two of the unit correlation line. Apart from that, microstructural investigations reveal that IP tests are prone to intergranular fracture whereas in OP tests trangranular fracture prevails given a clear indication of the prevailing damage mechanisms.