Influence of Rejuvenation Heat Treatment on Creep Property for Nickel-Based Directionally Solidified Superalloy

Creep is one of the most typical failure modes for the turbine blades of an aero-engine. The microstructure of the turbine blades after long-term service can be adjusted by rejuvenation heat treatment (RHT) to restore its creep properties. In this work, a series of RHT experiments were carried out on a directionally solidified (DS) nickel-based superalloy under different solution temperatures and primary aging temperatures based on the standard heat treatment (SHT) process parameters to investigate the mechanism of temperature influence on DS’s microstructure after RHT. It is indicated that a more uniform microstructure can be obtained under higher solution temperatures and lower primary aging temperatures compared to the SHT process. Furthermore, by employing the image processing methods to quantify microstructural parameters, a comprehensive indicator parameter for the RHT effect (marked as P_rej) was proposed to characterize the effects of RHT on DS superalloy’s microstructure and creep property combined with the entropy weight method. Based on this, a regression model to describe the relationship between RHT process parameters and P_rej was constructed by using the response surface methodology (RSM). It is revealed that the optimal solution temperature and primary aging temperature for this DS superalloy are 1283 °C and 1095 °C, respectively. Then the conclusion was validated through complete creep experiments on the DS superalloy, which showed the creep life after RHT reaches 95.5% of the SHT specimen, and the total life has increased by 20.6%.