PSI - Issue 68

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Structural Integrity Procedia 00 (2025) 000–000 Structural Integrity Procedia 00 (2025) 000–000

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Procedia Structural Integrity 68 (2025) 681–686

European Conference on Fracture 2024 Understanding of relationship between fracture and slip behaviour in Permendur alloys using multiscale mechanical testing of poly- and single crystalline specimens Yuki Tampa a , Yoji Mine a *, Daiki Kato b , Motoki Ohta c a Department of Materials Science and Engineering, Kumamoto University, 2‒39‒1 Kurokami, Chuo-ku, Kumamoto, 860-8555, Japan b Metallurgical Research Laboratory, PROTERIAL Ltd., 2107-2, Yasugi-cho, Yasugi, Shimane, 692-8601, Japan c Next Generation Tatara Co-Creation Centre, Shimane University, 1060 Nishikawatsu-cho, Matsue-shi, Shimane 690-8504, Japan Abstract In this study, we employed multi-scale tensile testing to correlate the brittle fracture behaviour of polycrystals with the slip behaviour of single crystals in FeCo and FeCo-2V Permendur alloys with focus on the effects of V addition and disordering. In the ordered-phase state, single crystalline specimens exhibited moderate ductility with specimen bending under uniaxial tensile loading conditions. This may be associated with shear banding due to the activation of multiple slip systems. Disordering caused the FeCo-2V alloy to exhibit discontinuous yielding with slip localisation and the following cross-slipping. For poly-crystalline specimens, the ordered-phase alloys exhibited some plasticity prior to brittle failure such as intergranular and cleavage cracking. The addition of V to FeCo increased the fracture strength since the more plastic accommodation reduced the local stress concentration in FeCo-2V. For ordered-phase multi-grains specimens, the bamboo-structured FeCo specimen behaved like a single-crystalline specimen in deformation behaviour, whereas in the FeCo-2Vspecimen with multiple grains in its transverse direction, plastic constraint by the neighbouring grains caused brittle fracture. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 1. Introduction The excellent soft magnetic properties of Permendur alloys with a B2 ordered-phase structure have expanded the range of applications in magnetic products that require miniaturization and high performance. However, in the ordered phase state, this alloy exhibits significant brittleness, Zhao et al. (1992), which makes it difficult to form by cold working. The addition of 2% V to FeCo alloys was found to improve their ductility to the point where cold rolling is available, White and Wahl (1932). In the FeCo-2V alloy, the ductility is improved by preventing the intergranular cracking that occurs during cold rolling of FeCo alloys, George et al. (2002). Since V plays a role in reducing the kinetics of ordering, V segregation at the grain boundaries presumably reduces the degree of ordering, which prevents the intergranular cracking, Glezer and Maleyeva (1988). By contrast, when polycrystalline European Conference on Fracture 2024 Understanding of relationship between fracture and slip behaviour in Permendur alloys using multiscale mechanical testing of poly- and single crystalline specimens Yuki Tampa a , Yoji Mine a *, Daiki Kato b , Motoki Ohta c a Department of Materials Science and Engineering, Kumamoto University, 2‒39‒1 Kurokami, Chuo-ku, Kumamoto, 860-8555, Japan b Metallurgical Research Laboratory, PROTERIAL Ltd., 2107-2, Yasugi-cho, Yasugi, Shimane, 692-8601, Japan c Next Generation Tatara Co-Creation Centre, Shimane University, 1060 Nishikawatsu-cho, Matsue-shi, Shimane 690-8504, Japan Abstract In this study, we employed multi-scale tensile testing to correlate the brittle fracture behaviour of polycrystals with the slip behaviour of single crystals in FeCo and FeCo-2V Permendur alloys with focus on the effects of V addition and disordering. In the ordered-phase state, single crystalline specimens exhibited moderate ductility with specimen bending under uniaxial tensile loading conditions. This may be associated with shear banding due to the activation of multiple slip systems. Disordering caused the FeCo-2V alloy to exhibit discontinuous yielding with slip localisation and the following cross-slipping. For poly-crystalline specimens, the ordered-phase alloys exhibited some plasticity prior to brittle failure such as intergranular and cleavage cracking. The addition of V to FeCo increased the fracture strength since the more plastic accommodation reduced the local stress concentration in FeCo-2V. For ordered-phase multi-grains specimens, the bamboo-structured FeCo specimen behaved like a single-crystalline specimen in deformation behaviour, whereas in the FeCo-2Vspecimen with multiple grains in its transverse direction, plastic constraint by the neighbouring grains caused brittle fracture. © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Keywords: Permendur, Tensile test, fracture, multiscale mechanical testing 1. Introduction The excellent soft magnetic properties of Permendur alloys with a B2 ordered-phase structure have expanded the range of applications in magnetic products that require miniaturization and high performance. However, in the ordered phase state, this alloy exhibits significant brittleness, Zhao et al. (1992), which makes it difficult to form by cold working. The addition of 2% V to FeCo alloys was found to improve their ductility to the point where cold rolling is available, White and Wahl (1932). In the FeCo-2V alloy, the ductility is improved by preventing the intergranular cracking that occurs during cold rolling of FeCo alloys, George et al. (2002). Since V plays a role in reducing the kinetics of ordering, V segregation at the grain boundaries presumably reduces the degree of ordering, which prevents the intergranular cracking, Glezer and Maleyeva (1988). By contrast, when polycrystalline © 2025 The Authors. Published by ELSEVIER B.V. Keywords: Permendur, Tensile test, fracture, multiscale mechanical testing

* Corresponding author. Tel.: +81-96-342-3713 E-mail address: mine@msre.kumamoto-u.ac.jp * Corresponding author. Tel.: +81-96-342-3713 E-mail address: mine@msre.kumamoto-u.ac.jp

2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 10.1016/j.prostr.2025.06.115 2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers 2452-3216 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers