Ultra-high ratio of ultimate strength to yield strength in L1₂ precipitates strengthening medium-entropy alloy

Strengthening via L1₂ nanoprecipitates is an effective approach to achieving excellent comprehensive mechanical properties in multi-principal element alloys (MPEAs). Although the conventional conflict between strength and ductility persists to a large extent, the difference between yield strength and ultimate strength is usually so small that it reflects weak deformation resistance of materials after yielding. In this study, we designed CoCrFeNiAlTi medium-entropy alloy (MEA), which exhibits yield strength of 801 MPa, ductility of 36.2 %, and intriguingly a very high ratio of ultimate strength to yield strength, demonstrating unusually strong strain hardening. Experimental results and analysis indicate that such comprehensive strength-plasticity synergy and strain-hardening behavior may be mainly attributed to the composition design and heterogeneous microstructure in the aged MEA.