TY - JOUR AU - Zhao, Shuyu AU - Bi, Xiaolin AU - Lu, Kaiju AU - Yuan, Zijian AU - Li, Taotao AU - Li, Ruifeng TI - Synergistic Strengthening and toughening in L-DED CoCrNi medium-entropy alloys: roles of dislocations and core-shell heterostructures JO - Microstructures PY - 2026 VL - 6 IS - 5 SP - EP - 104 SN - ISSN 2770-2995 (Online) AB -

To overcome the strength bottleneck of CoCrNi medium-entropy alloys (MEAs), this work systematically investigates the influence of Ti and Al addition strategies and ultrasonic impact treatment (UIT) on CoCrNi MEAs. Results indicate that the addition of TiAl master alloy promotes uniform dispersion of Ti-Al-O composite precipitates with a core-shell heterostructure, achieving synergistic enhancement of strength and plasticity. The alloy exhibits a yield strength (YS) of 589.1 MPa, an ultimate tensile strength of 973.5 MPa, and elongation of 34.4%. Further application of UIT refines the grain structure, induces high-density dislocations and stacking faults, and optimizes precipitate morphology. As a result, YS is enhanced to 692.7 MPa at 298 K and 997.7 MPa at 77 K, improvements of 17.6% and 40.6% compared to the as-deposited alloy. However, this strengthening is accompanied by a reduction in elongation, reflecting a typical strength-ductility trade-off. Despite the reduced ductility, UIT-treated alloy exhibits excellent strength at 77 K, highlighting its potential for cryogenic engineering applications where high strength is prioritized. Molecular dynamics simulations reveal the dynamic evolution of dislocation nucleation and stacking faults under impact loading. Quantitative analysis based on load-unload-reload testing indicates that heterogeneous deformation-induced strengthening provides a dominant contribution to the overall flow stress. The microstructural origin of this strengthening effect stems from the long-range stress fields and short-range obstruction effects arising from high-density dislocations, nanoprecipitates, and stacking faults introduced by UIT. These features continuously impede dislocation motion, thereby significantly enhancing deformation resistance.

KW - CoCrNi medium-entropy alloys KW - dislocations KW - heterogeneous deformation induced strengthening KW - laser-directed energy deposition KW - ultrasonic impact treatment DO - 10.20517/microstructures.2026.125 UR - https://dx.doi.org/10.20517/microstructures.2026.125