Microstructural evolution and elevated-temperature strengthening mechanism of Co-free FeCrMnNiV0.2Alx high-entropy alloys during annealing

We reported the influence of Al contents on microstructure and elevated-temperature mechanical properties in Co-free FeCrMnNiV0.2Alx (x = 0, 0.2, 0.3, 0.35 and 0.4) high-entropy alloys (HEAs), which were prepared by conventional cast and annealing methods. The results indicated that FCC + BCC structure was transformed into BCC/B2 structure with an increase of Al in as-cast HEAs, leading to an increase in Vickers hardness. After annealing, the formation of network spinodal decomposition structure in FCC regions led to an increase of hardness and strength with a sacrifice in ductility. Noted that the enhanced yield strength at elevated temperature of the cost-effective FeCrMnNiV0.2Al0.2 HEA can be ascribed to the stable strengthening phases, including sub-micron/nanoscale B2 phase in BCC regions and network FCC/L12 structure in FCC regions. The cracks prefer to propagate through either FCC regions or BCC regions with more secondary cracks.