Superior tensile properties induced by triple-level heterogeneous structures in the CoNiV-based medium-entropy alloy

• Published in: Journal of materials science & technology Vol. 214; pp. 245 - 254
• Main Authors: Xu, Luke, Ma, Yan, Zhang, Zihan, Yang, Muxin, Jiang, Ping, Zhu, Yuntian, Wu, Xiaolei, Yuan, Fuping
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.04.2025
• Subjects: Chemical short-range ordering; Hetero-deformation-induced hardening; Hetero-structures; Medium-entropy alloy; Precipitation hardening; Hetero-structures; Hetero-deformation-induced hardening; Chemical short-range ordering; Precipitation hardening; Medium-entropy alloy
• ISSN: 1005-0302
• DOI: 10.1016/j.jmst.2024.07.020

•The triple-level heterogeneous structures (THS) were achieved in (CoNiV)95Al3Ti2 medium-entropy alloy (MEA), comprising chemical short-range ordering at the atomic level, B2 nanoprecipitates at the nanoscale level, and heterogeneous grains at the microscale level.•The THS MEA exhibits a superior synergy between yield strength and ductility, with values ranging from 1.1 to 1.5 GPa and 18 % to 35 %, respectively.•A noteworthy enhancement in strain gradients and GND densities was observed at various interfaces, rather than within the interiors of grains.•Chemical short-range ordering regions effectively hinder the movement of dislocations, inducing significant lattice distortion and strengthening the alloy. The strength-ductility trade-off was evaded by deploying a triple-level heterogeneous structure into a CoNiV-based medium-entropy alloy (THS MEA). The innovative hetero-structures comprise chemical short-range ordering (CSRO) at the atomic level, B2 precipitates at the nanoscale level, and heterogeneous grains at the microscale level. The THS MEA exhibits superior mechanical properties, displaying a yield strength from 1.1 GPa to 1.5 GPa alongside a uniform elongation of 18 %-35 %. Compared with its coarse-grained (CG) counterpart, the THS MEA demonstrates the pronounced up-turn phenomenon and enhanced hardening behavior attributed to hetero-deformation-induced (HDI) hardening. The detailed microstructural characterizations reveal that CG MEA primarily accommodates deformation through extensive planar dislocations and Taylor lattices. However, the THS MEA exhibits a more complex deformation profile, characterized by planar and waved dislocations, deformation twins, stacking faults, and Lomer-Cottrell locks. Additionally, the interactions between dislocations and B2 nanoprecipitates play a pivotal role in dislocation entanglements and accumulations. Furthermore, the CSRO within the matrix effectively retards the dislocation motion, contributing to a substantive hardening effect. These findings underscore the potential of a heterogeneous microstructure strategy in enhancing strain hardening for conquering the strength-ductility dilemma. [Display omitted]