On the formation of hierarchical microstructure in a Mo-doped NiCoCr medium-entropy alloy with enhanced strength-ductility synergy

We demonstrate the formation of a hierarchical microstructure by optimized combination of Mo-doping and thermo-mechanical processing in a NiCoCr medium-entropy-alloy (MEA) that results in a significant improvement in yield-strength (similar to 775 MPa) and ultimate-tensile-strength (similar to 1200 MPa) with an elongation to fracture up to 35%. Addition of Mo slows down the recrystallization kinetics of the cold-rolled alloy at 700 degrees C. After 4 h annealing, the microstructure comprises soft recrystallized and hard non-recrystallized zones, dispersed sigma precipitates, annealing twins and retained stacking faults/nanotwins that are shown to contribute to the overall mechanical behavior. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.