Nano-mechanical Characterization for Metallic T. Ohmura Research Center for Structural Materials, National Institute for Materials Science (NIMS) Plastic deformation behavior is characterized through nano-mechanical testing in a small scale associated with microstructures including inter-phase and grain boundary. Plasticity initiation behavior was characterized for ferrite-cementite interface with different coherency in a pearlitic steel1). Transmission Electron Microscope (TEM) in-situ straining was applied to reveal dislocation-grain boundary interactions2,3). The mechanism of the slip transfer can be modeled in a simple dislocation reaction in the vicinity of grain boundary. Deformation mechanisms of plasticity initiation and subsequent behavior were modeled through stochastic analysis based on a pop-in phenomenon on a loading segment obtained from nanoindentation measurement4). The critical stress for the plasticity initiation shows Gaussian like distribution function, indicating a thermally-activated process including a nucleation of shear loop dislocation at defect-free region. In the subsequent stage, the loading curve shows intermittent plasticity, and the probability function for the event magnitude shows power-law type, suggesting a catastrophic phenomenon with a fractal dimension such as dislocation avalanche. References 1) 2) 3) 4) Mic T. Hatakeyama 1, K. Sawada 1, M. Suzuki 1 and 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) Modified 9Cr-1Mo steel (9Cr-1Mo-V-Nb steel) is a creep strength enhanced ferritic steel widely employed in boiler tubes and pipes in ultra-supercritical plants and as structural components in the nuclear industry. Laser powder bed fusion (LPBF) is recognized as a promising manufacturing process for producing the complex geometries. Additionally, improved performance is expected because of the unique microstructure formed through the extremely rapid solidification process. 44PP22--0011 MaterialsPP22--0022 rostructure of MIn this study, the microstructures of modified 9Cr-1Mo steels manufactured under various LPBF conditions were meticulously investigated [1]. The as-built samples exhibit a duplex structure composed of δ-ferrite and martensite. δ-ferrite was formed due to the extremely rapid cooling, on the order of 106 K/s, provided by the LPBF process. Conversely, martensite was derived from the austenite transformed from the δ-ferrite during reheating in the heat affected zone of subsequent laser scans. A higher energy density and random scan strategy result in a greater volume fraction of martensite, leading to a higher Vickers hardness at room temperature. In other words, it was suggested that the volume fraction and distribution behavior of δ-ferrite and martensite can be controlled by optimizing the LPBF parameters to achieve the desired mechanical properties. [1] T. Hatakeyama et al., Additive Manufacturing, 61 (2023) 103350. Y. H. Li, S. Gao, Y. Tomota, S. Ii, N. Tsuji, T. Ohmura, Acta Mater., 206, (2021) 116621. H. Li, S. Ii, N. Tsuji, T. Ohmura, Scripta Mater., 207, (2022) 114275. Y. Sato, S. Shinzato, T. Ohmura, T. Hatano, S. Ogata, Nature Comm., 11, (2020) 4177. Wang, Y. Tomota, T. Ohmura, odified 9Cr-1Poster Presentation ｜W. Gong, S. Harjo, M. Tanaka, Acta Mater., 196, (2020) 565-575. NIMS Award Symposium 2023Multi-scale Modeling in anufactured by Laser Powder Bed Fusion Mo Steel MM. Watanabe 1 P2 ｜ CharacterizationMechanical Behavior of
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