The precipitates evolution with related element interaction and redistribution during long-term high-temperature aging of Alloy 617

• Published in: Materials characterization 2023-05, Vol.199, p.112783, Article 112783
• Main Authors: Zhang, Zhiyang, Ding, Ran, Liu, Chenxi, Yu, Liming, Liu, Yongchang
• Format: Article
• Language: English
• Subjects: Alloy 617; Element redistribution; Mechanical properties; Phase transformation
• ISSN: 1044-5803
• DOI: 10.1016/j.matchar.2023.112783

The microstructural evolution during long-term thermal exposure of Alloy 617 is investigated in detail. During processing, various precipitation phases were formed, including MC, M23C6, M6C and γ', in which the M23C6 carbide is the primary strengthening phase and determines the hardness of Alloy 617. The M23C6 carbides can either form from decomposing MC or precipitate directly from the γ matrix, but they most eventually transformed to M6C carbides after long-term aging. In addition to the phase transformation among various carbides, the morphology evolution of M23C6 carbide is found to have a significant effect on the formation of γ' phase, which is closely related to the redistribution behavior of Al and Ti between M23C6 and γ matrix. We also identified a faster evolution kinetic of the precipitates at grain boundary than those in grain interior, which is caused by the different local diffusion rates. This work elucidates the transformation sequence among different precipitates and the corresponding alloy element redistribution behavior during aging Alloy 617, which shed lights on the strengthening phase design and can in turn optimize the mechanical properties of Alloy 617. •The study reveals the variation of precipitates during long-term aging and its strong link to the element diffusion and redistribution behaviors.•The morphology evolution of M23C6 carbide can promote the precipitation of γ' particles.•The evolution between different precipitated phases is much faster at grain boundary than that in grain interior.•M23C6 carbide is mainly strengthening phase, which determines the hardness of Alloy 617.