Thermoelectric Generation by Joining Interface Control of thermocouple M S. Meguro 1 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) Thermoelectric generation is one of promising technologies for actualization of carbon neutral society. However, it is still far from social implementation. Moreover, Seebeck coefficient of thermocouple metals is much lower than thermoelectric semiconductors. Nevertheless, we find that thermocouple metal joint with large area joining interface can generate current to some extent. In this study, we focused on combination of copper (Cu) and constantan (55Cu-45Ni) which are known as T type thermocouple. We investigated a thermoelectric generator module using 144-pair series connected copper-constantan laser welded joint. In this case, area of each joining interface is 0.4x12cm. In addition, thermoelectric generation of the module is available up to higher temperature than most of thermoelectric semiconductors. In this study, the large area joints are covered with oxidation-resistant coating and kept 1173K in a muffle furnace. As the result, the module generated 450mW thermoelectric power output in 800K over temperature gradient environment. On the other hand, result of microanalysis at joining interface shows steep distribution of each element. From the results, laser welding fabricates suitable joint for thermoelectric generation with steep joining interface. In the future, establishment of immobility high temperature waste heat collection system with the thermoelectric metal joint is expected. Unveiling the Transformation Pathways of Hierarchical γ90 – εtwin – α’ Triple Phase Structure Formation at ε-ε M D. Singh1, 1 National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 2 University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305–8577, Japan 48PP22--0099 PP22--1100 W. Tasaki2, F. Yoshinaka1, S. Takamori1, S. Emura1, K. Tsuchiya1,2 and T. Sawaguchi1* Deformation-induced martensitic transformation (γ-austenite Poster Presentation ｜NIMS Award Symposium 2023 artensite Intersection P2 ｜ Characterization→ ε/α’-martensite) in austenitic steels has garnered significant interest owing to its transformation-induced plasticity effect. To elucidate the orientation-dependent intricate γ/ε/α’ phase microstructure at deformation induced ε – ε intersection, a single crystal of 316 austenitic stainless steel was compressed along the [001]γ axis at a cryogenic temperature (173 K). Electron backscattered diffraction analysis was employed to reveal the deformed microstructure on the (110)γ surface. A hierarchical triple phase structure was discovered at ε–ε intersection, where the γ rotated 90º from the matrix (γ90), {101�2 } ε-twin, and α’ phases coexist. Depending on the operative shear angle with a common intersection axis, either 90º (Type I) or 30º (Type II), three distinct atomic rearrangements of the intersection volume were observed: γ90 was present at Type I intersection, and α’-phase was developed at Type II intersection, respectively. {101�2} ε-twin also occurred at Type I intersection, serving as an accommodation mechanism alongside the intersection γ90. Transformation paths for three intersection products were visualized by the unified tetrahedron model, considering T/2 or T/3 γ-twinning shear as an intermediate state. Moreover, a novel scheme is proposed to index the α’-martensite crystallographic variants at ε–ε intersections by establishing a correlation between the Bain distortion and double shear process. etals
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