Liquid helium temperature deformation and local atomic structure of CoNiV medium entropy alloy. (March 2022)

• Record Type: Journal Article
• Authors: Nutor, Raymond Kwesi; Xu, Tianding; Wang, Xuelin; Wang, Xiao-Dong; An, Pengfei; Zhang, Jing; Hu, Tiandou; Li, Laifeng; Cao, Qingping; Ding, Shaoqing; Zhang, Dongxian; Jiang, Jian-Zhong
• Is Part Of: Materials today communications. Volume 30(2022)
• Publication Date: 2022-03
• Subjects: Medium entropy alloy -- Mechanical property -- EXAFS -- DFT; Materials science -- Periodicals; 620.11
• DOI: 10.1016/j.mtcomm.2022.103141
• Languages: English
• ISSNs: 2352-4928

Abstract

Abstract: Equiatomic CoNiV is now known to be the strongest fcc-structured equiatomic medium entropy alloy (MEA) with a high lattice friction stress. The local structure of CoNiV is measured using the extended x-ray absorption fine structure (EXAFS) and fitted to a fully disordered CoNiV lattice structure. EXAFS analysis suggests the bond length between V and its neighbors is significantly larger compared to the bond length of Co and Ni to its neighbors. Density functional theory (DFT) calculations reveal that the high friction stress is due to fluctuating atomic bond lengths and charge transfer between V and Co/Ni atoms. Cryogenic tensile tests also show that the tensile strength and ductility both increase with decreasing temperature up to liquid helium temperature (4.2 K). EBSD and TEM investigations suggest dislocation-mediated plasticity persists from ambient to liquid helium temperature due to the high stacking fault energy of the CoNiV MEA. This makes CoNiV the first of its kind in displaying enhancements in strength and ductility without any additionally activated deformation mechanisms. Graphical Abstract: ga1