The Effect of Temperature and Phase Shift on the Thermomechanical Fatigue of Nickel-Based Superalloy

In this paper, the minimum temperature and phase shift effects on the thermo-mechanical fatigue (TMF) behavior of Inconel 713LC are investigated. TMF tests were performed under 0 degrees (in-phase-IP) and +180 degrees (out-of-phase-OP) phase shifts between mechanical strain and temperature. Cylindrical specimens were cycled at constant mechanical strain amplitude with a strain ratio of R-epsilon = -1. Tests were performed with temperature ranges of 300-900 degrees C and 500-900 degrees C. The heating and cooling rate was 5 degrees C/s. Fatigue hardening/softening curves and fatigue life data were assessed. Results show that out-of-phase loading was less damaging than in-phase loading. Scanning electron microscopy (SEM) examination of metallographic sections indicated that the life-reducing damage mechanism was intergranular cavitation under in-phase loading. Transmission electron microscopy (TEM) revealed honeycomb structures for IP loading. The plastic strain localization into persistent slip bands was typical for OP loading. For out-of-phase loading, fatigue damage appeared to be dominant. The increase in the temperature range led to a significant decrease in fatigue life. The reduction of fatigue life was far more pronounced for out-of-phase loading. This can be ascribed to the accelerated crack propagation at high tensile stress under out-of-phase loading as well as the amount of accommodated plastic strain deformation. Based on the SEM scrutiny of metallographic sections and TEM observations of dislocation arrangement, the prevailing damage mechanisms were documented and the lifetime behavior was accordingly discussed.

Automated summary

This paper investigates the effects of minimum temperature and phase shift on the thermo-mechanical fatigue behavior of Inconel 713LC. The results show that out-of-phase loading is less damaging than in-phase loading, with intergranular cavitation being the main damage mechanism for in-phase loading, and honeycomb structures and plastic strain localization being typical for out-of-phase loading. The increase in temperature range significantly reduces fatigue life, especially for out-of-phase loading. The prevailing damage mechanisms and lifetime behavior are discussed based on SEM and TEM observations.