Microstructures Evolution of a Second Generation Single Crystal Superalloy after Long Term Aging at 980°C

Abstract

The microstructure evolution of the second-generation single crystal superalloy DD412 aged at 980°C for 1000 h were investigated. The results show that needle-shaped topologically close packed (TCP) phases rich in Re and W were firstly found in the dendritic core region after aging at 980°C for 400h, while the size and amount of TCP phases increased gradually with aging time, which is due to the fact that high melt point elements Re and W segregated to the dendritic core region. With the increment of aging time, the size of γ′ phase increased and volume fraction of γ′ phase decreased. The γ′ phase in dendrite core and inter-dendrite region remained cuboidal basically, and the γ′ phase in second dendritic arm showed directional coarsening after aging for 800 h. The MC carbides in inter-dendritic region decomposed gradually and transformed to the M6C carbides partially during long term aging, while few fine blocky M6C carbides precipitated in dendritic core after aging for 400h. The different microstructure evolution in dendritic region is due to the dendrite segregation of alloying elements and elements diffusion during aging.