Deformation and damage mechanisms in IN792 during thermomechanical fatigue

The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystalline superalloy IN792 have been investigated. The TMF cycles used in this study are in-phase (IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 °C while the maximum temperature is 500 or 750 °C in the IP TMF-tests and 750, 850 or 950 °C in the OP TMF-tests. The majority of the cracks are transcrystalline, except for the IP TMF-test at 750 °C, where some tendency to intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated in locations where deformation structures such as deformation bands have formed in the material. In the temperature interval 750–850 °C, twins were formed in both IP and OP TMF-tests and this behaviour is observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observed for tests with a lower (500 °C) and a higher (950 °C) maximum temperature. Recrystallization at grain boundaries, around particles and within the deformation structures have occurred in the OP TMF-tests with a maximum temperature of 850 and 950 °C and this is more apparent for the higher temperature. Void formation is frequently observed in the recrystallized areas even for the case of compressive stresses at high temperature.