Identification of fatigue crack growth mechanisms in IN100 superalloy as a function of temperature and frequency

A study is undertaken to investigate the fatigue crack growth rate properties of polycrystalline IN100 through the identification of crack growth mechanisms as a function of temperature, frequency and K. An additional goal is to determine the stress free activation energy of IN100. Constant amplitude, load controlled tests are performed at room temperature (22 degrees C), 316 degrees C, 482 degrees C and 649 degrees C under two different loading frequencies of 20 and 0.33 Hz. These specimens are then analysed via scanning electron microscopy (SEM) to determine failure mechanisms. SEM shows that, as temperature increased from room temperature to 649 degrees C, the fracture mechanism transitions from transgranular to intergranular. The fracture mechanism is shown to transition from intergranular to transgranular at elevated temperatures as da/dN increases as a result of growing K. Scanning electron microscopy shows that, as frequency decreases from 20 to 0.33 Hz at 649 degrees C, the fracture mechanism transitions from transgranular to intergranular.