Gaseous Hydrogen Embrittlement of Pure Nickel and Copper Nickel Alloys K. 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) 2 Department of Mechanical Engineering, Fukuoka University Pure nickel is one of the materials whose ductility is severely degraded by high-pressure hydrogen gas. For triggering the hydrogen embrittlement of pure nickel, hydrogen accumulation along grain boundaries is required. To achieve the accumulation, two mechanisms have mainly been suggested: (1) hydrogen trapping at the grain boundaries and (2) hydrogen transportation by moving dislocations. In the present study, the contribution of the above mechanisms on the hydrogen embrittlement of pure nickel is firstly discussed based on the experimental results at a cryogenic temperature. Then, the effects of copper addition on the dominant mechanism are evaluated. It was revealed that the alloy is embrittled mainly by the trapped hydrogen when the nickel fraction is more than 80%. However, when the nickel fraction decreased to be less than 80%, the hydrogen transportation by moving dislocation started contributing to the hydrogen embrittlement. The reason was discussed in terms of the nickel fraction dependence on the ability of hydrogen trapping along the grain boundaries. Magnetic Order and Phase Transformation in Fe S. Morooka 1,2, M. Koyama 3, T. Kawasaki 2 and S. Harjo 2 1 Materials Science Research2 J-PARC Center, Japan Atomic Energy Agency (JAEA) 3 Institute for Materials Research, Tohoku University Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. In particular, medium Mn steel with a nominal chemical composition of Fe-5.0Mn-0.1C (mass%) fabricated by intercritical annealing 923 K for 1.8 ks after cold-rolling, was the high-strength mechanical properties at low temperature. This strengthening mechanism evaluated by means of in-situ neutron diffraction under low temperature (engineering materials diffractometer (TAKUMI) at Japan Proton Accelerator Research Complex (J-PARC)), electron back scatter diffraction (EBSD), low temperature differential scanning calorimetry (DSC) and low temperature magnetic susceptibility measurement. We found that as the sample temperature decreases, face-centered cubic (FCC) structure transferred face-centered tetragonal (FCT) structure. Namely, it suggests that austenite transformed martensite like Fe-Pd or Fe-Pt alloy. Therefore, the origin of the high-strength mechanical properties at low temperature was in the presence of FCT martensite. This study got partially support from MEXT Program: Data Creation and Utilization Type Material Research and Development (JPMXP1122684766). Wada 1 and J. Yamabe 2 Center, Japan Atomic Energy Agency (JAEA) Poster Presentation ｜NIMS Award Symposium 2023 P3 ｜ Evaluation-Mn-C Alloy at Cryogenic Temperature PP33--0077 PP33--0088 61
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