Effects of Mn Content and Grain Size on Hydrogen Embrittlement Susceptibility of Face-Centered Cubic High-Entropy Alloys
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en embrittlement is attributed to plasticityassisted cracking at specific microstructures.[1] In particular, it can be triggered by grain boundary cracking
MOTOMICHI KOYAMA is with the Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Miyagi, 980-8577, Japan and also with the Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan. Contact email: [email protected] HAOYU WANG is with the Institute for Materials Research, Tohoku University and also with the Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University, Aramaki Aza Aoba, Aoba-ku, Sendai, Miyagi, Japan. VIRENDRA KUMAR VERMA is with the Institute for Materials Research, Tohoku University and also with the Department of Mechanical Engineering, Kyushu University, Motooka 744, Nishi-ku, Fukuoka, 819-0395, Japan. KANEAKI TSUZAKI is with the Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University also with the Department of Mechanical Engineering, Kyushu University also with Research Center for Hydrogen Industrial Use and Storage (HYDROGENIUS), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan and also with the Research Center for Structural Materials, National Institute for Materials Science, 1-2-1, Sengen, Tsukuba, Ibaraki 305-0047, Japan. EIJI AKIYAMA is with the Institute for Materials Research, Tohoku University. Manuscript submitted April 16, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
after significant plastic deformation.[2] Accordingly, grain boundary strength and microstructural stress concentration at grain boundaries are key to controlling the resistance to hydrogen embrittlement. From the perspective of hydrogen embrittlement resistance, face-centered cubic (FCC) alloys such as austenitic steels and Ni alloys have been previously noted as hydrogen-resistant materials.[3–5] In FCC alloys, enhancement of dislocation planarity increases number of dislocations piling-up on a single slip plane, which increases stress concentration at obstacles such as grain boundaries. The stress concentration assists hydrogen segregation and cracking. Therefore, the hydrogen embrittlement susceptibility of these alloys is strongly dependent on the stacking fault energy[6] and the degree of short-range ordering of solute atoms,[7] as these are the primary factors that affect dislocation planarity. However, the superior work hardenability and elongation of recent structural FCC alloys stems from the high dislocation planarity and associated twinning/transformation [8,9]; therefore, we must establish a strategy for improving the resistance to hydrogen embrittlement of FCC alloys that exhibit planar dislocation slip. As advanced FCC alloys, CrCoFeMnNi high-entropy alloys (HEAs) have recently drawn attention,[10–12] and these also show high dislocation planarity associated with low stacking fault energies and short-range ordering.[13–15] For instance, an equiatomic CrCoFeM
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