Thermo-mechanical fatigue tests on MarM-247 nickel-based superalloy using the direct resistance method

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.