Deep Drawing Behavior of CoCrFeMnNi High-Entropy Alloys

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I.

INTRODUCTION

MULTI-PRINCIPAL element alloys, also referred to as high-entropy alloys (HEAs), have attracted considerable attention due to their great potential.[1–7] HEAs consist of five or more alloying elements in equiatomic or near-equiatomic composition based on the primary design concept to maximize the configurational entropy of mixing (DSmix) and to obtain a random solid solution with simple microstructures, such as simple face-centered-cubic (fcc), body-centered-cubic (bcc), or fcc + bcc.[8,9] Since the early design efforts by Cantor,[10] Yeh,[11] and Ranganathan[12] in this new class of alloy, numerous HEAs have been extensively studied. The single-phase bcc-structured HEAs are regarded as promising high-temperature materials owing to their high softening resistance at high temperatures and sluggish diffusion phenomena.[7,13,14] The single-phase fcc-structured HEAs, such as equiatomic CoCrFeMnNi,[10,15] show high strength attributed to solid solution hardening and good ductility with a large number of slip systems of fcc at room temperature. JAE WUNG BAE, JONGUN MOON, MIN JI JANG, JAIMYUN JUNG, and DAMI YIM are with the Department of Materials Science and Engineering, POSTECH (Pohang University of Science and Technology), Pohang, 790-784, South Korea. DONG-HYUN AHN is with the Korean Atomic Energy Research Institute, Daejeon, 34057, South Korea. SOO-HYUN JOO is with the Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan. HYOUNG SEOP KIM is with the Department of Materials Science and Engineering, POSTECH (Pohang University of Science and Technology), and also with Center for High Entropy Alloys, POSTECH (Pohang University of Science and Technology), Pohang 790-794, South Korea. Contact e-mail: [email protected] Manuscript submitted October 11, 2016.

METALLURGICAL AND MATERIALS TRANSACTIONS A

More recently, dual-phase HEAs are getting attention due to their good mechanical response originated from the stress and strain partitioning between ductile fcc phase and hard bcc phase.[16] Zaddach et al.[17] have studied the mechanical properties and stacking fault energy (SFE) of CoCrFeMnNi alloy. Their observed SFE of the CoCrFeMnNi alloy was 25 mJ/m2, which is lower than those of pure Ni and NiFe. Moreover, Gludovatz et al.[18] reported that the CoCrFeMnNi alloy shows exceptional fracture-toughness and an outstanding combination of high strength and high ductility, with the presence of deformation-induced nano twins at cryogenic temperatures. Otto et al.[15] observed the temperature dependence of mechanical properties and deformation behavior. Continuous steady strain hardening, resulting from dislocation activity and pronounced deformation twinning, was observed at 77 K (196 C), which is in contrast with dislocation-dominated deformation observed at room temperature. The exceptional mechanical properties of HEAs at various temperatures and the considerable number of recipes for designing HEA alloys make them a new research frontier. As mentioned above, many researchers have focused

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