Influence of test parameters on the thermal-mechanical fatigue behavior of a superalloy

The thermal-mechanical fatigue (TMF) behavior of IN-100, a cast nickel-base superalloy, was investigated with a basic mechanical strain-temperature loop applied in a temperature range from 600 °C to 1050 °C (873 to 1323 K). Peak strains were applied at intermediate temperatures, giving a faithful simulation of real component parts. Tests with or without a mean strain were used; other tests involved a longer period or a tensile hold time, and they were compared with conventional “in-phase” TMF cycles. An interrupted test procedure was used with a plastic replication technique to define a conventional TMF life to 0.3-mm crack depth, as well as a life to 50-µm, crack depth, to characterize the crack initiation period. Some stress-strain hysteresis loops were reported. Thermal-mechanical fatigue life was found to be dependent upon test parameters, while the life to crack initiation was not. Oxidation of specimens and micro-cracks was found to be important in all the tests. These results were then discussed and compared with those under low cycle fatigue at high temperature.