Microstructure evolution of creep damaged DZ411 superalloy during rejuvenation heat treatment

Abstract

The simple solution and aging treatment processes were adopted to rejuvenate the microstructure of creep damaged DZ411 superalloy. The microstructure evolution of superalloy during rejuvenation process was investigated by OM and SEM, and then the mechanical properties were evaluated by tensile and creep rupture tests. The results show that creep damaged superalloy obtained from interrupted test at the end of secondary stage of creep suffers from the spheroidization and rafting of the prime γ′ phase and vanishing of the secondary γ′ phase, but no creep cavities. It is also found that the solution treatment plays a prime role in dissolution of deformed γ′ phase, and then re-precipitation of fine γ′ phase. The proper solution temperature can effectively avoid incipient melting and recrystallization. The two stages of aging are the dominant procedures of optimizing the size, shape and volume ratio of bimodal size γ′ phase. By the appropriate rejuvenation schedule, the bimodal size γ′ particles with coarse secondary γ′ particles and fine tertiary γ′ particles can be obtained. The average diameters of bimodal size γ′ particles are about 0.38 μm and 0.07 μm, and the volume fraction are 47.5% and 6.5% respectively. Rejuvenation heat treatment can successfully recover the room temperature strength close to that of the original alloy. The creep rupture life and elongation of rejuvenated DZ411 superalloy under condition of 980 ℃/220 MPa are 121 h and 13%, these values are slightly lower than that of the original alloy.

Keywords

• directionally solidified superalloy
• creep damage
• rejuvenation heat treatment
• microstructure
• properties