Nondestructive evaluation of fatigue damage in ULTIMET® superalloy

Acoustic emission (AE) and positron spectroscopy were used to study fatigue damage in ULTIMET alloy. The linear-location method of AE was employed for identifying the positions of crack initiation for a cylindrical specimen subjected to fatigue. Positron lifetime spectroscopy, as a sensitive nondestructive technique, was utilized to reveal the fatigue damage. The results obtained by the AE system were generally in good agreement with those of the average positron lifetimes by positron spectroscopy. The detected crack initiation was further investigated by scanning electron microscopy, which was found to be consistent with the AE and positron spectroscopy results. The crack-initiation stage of ULTIMET alloy subjected to high-cycle fatigue was characterized.