Microstructure evolution and rejuvenation heat treatment of service superalloy

Microstructure evolution of (special character presented)C6y superalloy and influence of rejuvenation heat treatment on microstructure of the alloy were investigated. The results show that γ' particles which are the major strengthening phase of alloy degenerate at high temperature after long time service. The mechanism of γ' coarsening are Ostwald ripening and particles agglomeration. The morphology characteristic parameters of γ' particle represent the degenerate behavior. MC carbides decompose at high temperature and transform into M₆C carbides enveloped with γ film. Under certain conditions M₆C carbides precipitate in the γ matrix. The carbides located at the grain boundary have a stronger tendency of decomposition than the intragranular. Discontinuous M₆C carbides with γ film generate at the grain boundary. The size, shape and distribution of γ' phase are optimized and hardness of the alloy are recovered by this rejuvenation heat treatment, by which serrated grain boundary forms and creep rupture property is restored to extend the service life of the superalloy.