Mitigate the strength-ductility trade-off in high Cr content Ni₂Cr₂Fe MEA via heterogeneous structure design

High-entropy and medium-entropy alloys (HEAs/MEAs) with face-centered cubic (FCC) structures have attracted significant interest. However, their low strength limits their use in structural applications. Traditional strengthening methods often sacrifice ductility to improve strength. This issue is particularly severe in Co-free alloys with high Cr content, which tend to form brittle precipitates during heat treatment. This study aims to mitigate the strength-ductility trade-off in a Co-free Ni₂Cr₂Fe MEA through a heterogeneous grain structure. After cold rolling and short-term high-temperature annealing (950 °C, 2 min), the alloy exhibits a yield strength of 1009 MPa and a fracture elongation of 21 %, without second phase strengthening or complex alloying. The microstructure includes non-recrystallized regions (NRX) with high dislocation density and recrystallized regions (RX) with ultrafine grains. Dislocation strengthening in the NRX regions contributes mainly to the yield strength. The sub-structures in the deformed regions sustain plastic deformation and promote uniform strain distribution. These findings provide insights into improving the strength-ductility balance in high-Cr content alloys.