Effect of rejuvenation heat treatment on microstructure and hot corrosion resistance of a service-exposed nickel-based gas turbine blade

Abstract

The present work was carried out to evaluate the effect of rejuvenation heat treatment on recovery of the microstructure and hot corrosion resistance of a service-exposed nickel-based gas turbine blade. Different rejuvenation heat treatment cycles were carried out on the service-exposed blade. The microstructure of the blades was examined by scanning electron microscope (SEM) in as-received condition and after rejuvenation heat treatment. Both of the service-exposed and rejuvenated blades were subjected to cyclic hot corrosion tests to evaluate the resistance to hot corrosion. Microstructural investigations showed that the rejuvenation heat treatment cycle, including solution treatment at 1175 °C for 3h, followed by air cooling and two-stage aging treatments at 925 °C/1h and 845 °C/24 h was most successful to recover the microstructure of the service-exposed blade to its virgin condition. Moreover, it was found that the rejuvenation heat treatment has a significant effect on the hot corrosion resistance of the service-exposed blade via dissolution of continuous grain boundary carbide films and the redistribution of the elements in the alloy matrix. The results of the hot corrosion experiments showed that the rejuvenation heat treatment can improve the hot corrosion resistance of the service exposed blade up to about 60 percent.