40PP11--1111 Effect of Cooling Rate from Sub-Solvus Solution Treatment Temperature on Hardness in Powder M T. Saito1, T. Shibayama2, T. Osada1, M. Okuno3, D. Nagahama3 and T.T. Sasaki1 1 National Institute for Materials Science (NIMS), 2 Mitsubishi Heavy Industry, Ltd, Powder metallurgy (P/M) processed TMP5002 (HGN200) has been developed by mixing conventional Ni-based and Co-based superalloys with γ-γ’ two-phase microstructure and is known as a Ni-Co-based superalloy with the highest temperature capability of 740 °C among P/M Ni-based superalloys1). Sinc the excellent high-temperature capability, i.e., high strength, is due to the dispersion of γ’ precipitates, the ideal microstructure must be developed during the solution treatment and subsequent artificial aging, which is carried out within a practically acceptable time, and the precipitation of γ’ must be utilized during cooling process. The cooling rate from the solution treatment temperature is crucial for the cooling γ’ precipitation. This work investigated the effect of the cooling rate from the solution treatment temperature on the room temperature properties in P/M TMP5002 alloys. The samples were solution-treated at a sub-solvus temperature of 1110 °C for 4 h and then cooled at different cooling rates. The samples were then subjected to standard two-step aging at 650 °C for 24 h and at 760 °C for 16 h. The highest room temperature hardness of the aged sample is achieved in the sample cooled at 100 °C/min, but further increase in cooling rate tends to decrease the hardness. Atom probe tomography and SEM analysis revealed that the composition of the γ’ reached the equilibrium composition at 760 °C, and the volume fraction of γ’ precipitates in the two-step aged sample is similar regardless of the cooling rate. Therefore, we can conclude that the dispersion of a high volume fraction of nanoscale γ’ with approximately 30 nm diameter is important to maximize the strength. Reference: 1) Y. F. Gu, et al., Proc. 13th Int. Conf. on Superalloys, (2016), 210. Three-Dimensional Cellular Automaton for Grain Growth of Inconel 738LC in Laser Powder Bed Fusion M. Kusano 1 and M. Watanabe1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) Laser powder bed fusion (L-PBF), one of additive manufacturing techniques, can fabricate a near-net shape product by repeating powder spreading on the platform and selective scanning of the focused laser. The fabricated part undergoes a cyclic thermal history involving melting and solidification through the process. Consequently, epitaxial and competitive growth in such thermal cycles results in the formation of complex solidification microstructures. The objective of the current study was to predict such microstructure so that a three-dimensional cellular automaton (3D-CA) model was developed by coupling with a finite element thermal analysis for a nickel superalloy Inconel 738LC in the process. The 3D-CA results showed that columnar crystal grains along the building direction, which were strongly influenced by laser scanning conditions. Validation by comparison with microscopic observations of the fabricated samples confirmed that the developed 3D-CA model was effective in predicting solidification microstructures in L-PBF. etallurgy Ni-Co-base Superalloy PP11--1122 1 Poster Presentation ｜NIMS Award Symposium 2023 P1 ｜ Process3 Honda R&D Co., Ltd
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