Some cracks were found at the first stage discs of gas turbine rotors made of Ni-base superalloy. There were inter-granular cracking and observed to be highly stressed and damage sensitive locations with less potential for oxidation, which is thought to occur due to hold-time cracking. In this study, laser peening technology was developed to improve fatigue properties of Ni-base superalloy Alloy 706, and the effects on the material properties were examined. Laser peening is a novel process to induce compressive residual stress on material surface by irradiating focused high-power laser pulses. Several durability tests, such as thermal aging treatment test and stress aging test, were performed under thermal power plant operation conditions, and the effectiveness of laser peening treatment was confirmed.
