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Element Effects of Mn and Ge on the Tuning of Mechanical Properties of High-Entropy Alloys TU-NGOC LAM, CHE-WEI TSAI , BO-KAI CHEN, BO-HONG LAI, HUNG-CHIH LIU, TAKURO KAWASAKI, STEFANUS HARJO, BI-HSUAN LIN, and E-WEN HUANG Substitution of Ge for Mn increases the elastic moduli of different {h k l} orientations of the CoCrFeMnNi-based high-entropy alloy. Our findings indicate that tuning minor element compositions may result in improved strength–ductility combination. The underlying deformation mechanisms of CoCrFeNiGe0.3 were examined by in situ neutron diffraction and analysis of the associated diffraction profiles during tensile deformation. The strain-hardening response of CoCrFeNiGe0.3 exhibited a dominant mechanism of mechanical twinning at moderate and large strains at room temperature. The evolution of the bulk work hardening rate was consistent with the convolutional multiple whole profile fitting results, which exhibited a continuous increase in twin formation probability. The microstructural development was also investigated by transmission electron microscopy, which revealed the formation of huge amounts of deformation twins in CoCrFeNiGe0.3 at room temperature. https://doi.org/10.1007/s11661-020-05932-9  The Minerals, Metals & Materials Society and ASM International 2020

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INTRODUCTION

HIGH strength and good ductility are the two most important properties of high-entropy alloys (HEAs).[1,2] Among the most commonly reported HEAs, the quinary CoCrFeMnNi, whose constituent elements are all transition metals with negligible differences in atomic size and electronegativity, has been extensively studied and gradually understood in terms of its mechanical

TU-NGOC LAM is with the Department of Materials Science and Engineering, National Chiao Tung University, 1001 University Road, Hsinchu 30010, Taiwan, ROC and also with Department of Physics, College of Education, Can Tho University, Can Tho City 900100, Vietnam. Contact e-mail: [email protected] CHE-WEI TSAI and HUNG-CHIH LIU are with the Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC and also with the High Entropy Materials Center, National Tsing Hua University, Hsinchu 30013, Taiwan, Taiwan, ROC. BO-KAI CHEN and BO-HONG LAI are with the Department of Materials Science and Engineering, National Chiao Tung University. TAKURO KAWASAKI and STEFANUS HARJO are with the J-PARC Center, Japan Atomic Energy Agency, 2-4 Shirane Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan. BI-HSUAN LIN is with the National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan, ROC. E-WEN HUANG is with the Department of Materials Science and Engineering, National Chiao Tung University and also with the High Entropy Materials Center, National Tsing Hua University. Manuscript submitted February 24, 2020.

METALLURGICAL AND MATERIALS TRANSACTIONS A

response and its dominant deformation mechanism at cryogenic, ambient, and high temperatures.[3–16] However, the addition of Mn causes a decrease in oxidation re