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Shaofeng Chen,Naicheng Sheng,Shigang Fan,Shijie Sun,Guichen Hou,Jinguo Li,Lirong Liu,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.12
The effects of sulfur on the microstructures and solidification characteristics of a second-generation single crystal superalloywere clarified through optical microscope (OM), scanning electron microscope (SEM), differential scanning calorimetry(DSC) and electron probe microanalysis (EPMA). When sulfur was added to the alloy, the area fraction of theeutectic and microporosity decreased with the area fraction of MC carbides increasing. The γ / γ’ eutectic morphologychanged from mosaic + fan + coarse γ’ to mosaic + fan as the sulfur content increased, and very few γ / γ’ eutectic wasfound in the alloy with the highest sulfur content. Moreover, sulfur tended to segregate at the interdendritic regions andform Hf / Cr- rich sulfides, which were adjacent to the carbides or eutectic. This work not only uncovers some sulfideswrapped by eutectic or carbides, but also presents the solidification sequence of the interdendritic regions in high sulfurcontent alloy was discussed.
Microstructural Evolution of a High W Content Ni-Based Superalloy at γ′ Sub-Solvus Temperatures
Sigeng Zhou,Naicheng Sheng,Shijie Sun,Shigang Fan,Jinjiang Yu,Guichen Hou,Jinguo Li,Yizhou Zhou,Xiaofeng Sun 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.1
The evolution of γ′ phase and γ/γ′ eutectic during short-time heat treatment of the Ni-based superalloy with high W content,K416B are investigated. In this study, high temperature Differential Scanning Calorimetry (DSC) is employed to designthe heat treatment experiments and the precipitate temperature of secondary γ′ is found in the cooling curve. The standardcoarsening model is applied to figure out the coarsening rate constant of γ′ precipitate. On this basis, a novel method isproposed to predict the globularization time of γ phase in γ/γ′ eutectic during the heat treatment process. As holding temperatureincreases, more γ lamellae convert to platelets before reaching thermodynamic equilibrium. Electron microscopyobservations exhibit the boundary splitting and necking formation on the γ plate surface. Moreover, the dissolution kineticsof γ phase is quantitatively assessed by JMAK model. The volume fraction descends rapidly in the initial stage, and thenreach to a threshold. Above proposed approaches are validated via various heat treatment experiments.