Effect of aging heat treatment on the microstructure and hardness of a serviced ZHS32 superalloy

Abstract

According to the gradual changes of the microstructure of superalloys during harsh service condition of turbine blades and the detrimental effects of these changes on the mechanical properties of superalloys, performing of a rejuvenation heat treatment (solution treatment + aging process) on ex-serviced superalloys is necessary. In this work, the aging heat treatment was conducted on a serviced single crystal ZHS32 superalloy in the temperature range of 950-1150°C. It was found that while performing the aging process at 950 and 1050°C for 10 h did not provide appropriate conditions for the nucleation and growth of primary ϒ′ phases, conducting aging at the temperature of 1150°C for 10 and 16 h yields to the formation of ϒ′ precipitates with the desired cuboidal morphology. The comparison of the microstructure of the rejuvenated samples with the un-rejuvenated samples confirms that with applying this procedure, the size of strengthening ϒ′ precipitates reduces and the volume fraction of these phases considerably increases, which yields to the recovery of the superalloy microstructure and improvement of its mechanical properties such as hardness.