Rejuvenation of IN738LC gas-turbine blades using hot isostatic pressing and a series of heat treatments

Abstract

The maintenance of the gas turbine blades is important because these blades are operated in harsh conditions. Therefore, nickel-based superalloys that offer excellent performances in high-temperature conditions are typically used, and the blades are inspected and replaced based on the manufacturer’s maintenance standards. However, the service life can be extended by refurbishing the blades that have exceeded their warranty life, based on the manufacturer criteria. In this study, 10 rejuvenation conditions that consist of ‘hot isostatic pressing and series of heat treatment’ were applied to the blades that operated in domestic environments and had exceeded their warranty life. First, through microstructure analysis, by comparing the shape of the gamma prime phase according to the change of the full solution temperature, the optimal full solution temperature was selected to be 1200 °C or more and less than 1220 °C. Based on this, the tensile properties according to the presence or absence of HIP process and the detailed heat treatment conditions were evaluated, and the optimal rejuvenation conditions was selected by comparing tensile strength, yield strength, and elongation values. Finally, to verify the selected rejuvenation condition, the creep durability was evaluated, and it was confirmed that the creep life of the used material with a reduced creep life of 40 % compared to the new material was restored similarly to the new material.