Precipitation-assisted heterostructure in a FeMnCoCrCuC high entropy alloy enables superior mechanical property

High-entropy alloys in which the face-centered cubic structure is dominant cannot meet practical engineering application requirements due to their insufficient strength. Traditional strengthening methods can improve strength of materials, but they inevitably lead to decreased ductility. In this work, mechanical properties of a face-centered cubic-structured FeMnCoCrCu high-entropy alloy were improved by doping a substantial amount of carbon and employing a processing route that combines cold rolling and annealing. A dual-heterostructure characterized by both bimodal grain-size distribution and non-uniform distribution of nanoscale precipitates was constructed. The average grain sizes were 21.6 and 5.9 μm for the coarse and fine grains, accounting for 56.6% and 43.4% of the material, respectively. On the other hand, the finer M23C6 precipitates in the grain interior had an average size of 73.1 nm, constituting 3.4% of the coarse-grained region and 10.7% of the fine-grained region. The larger M23C6 precipitates at grain boundaries had an average size of 182.4 nm, with an overall volume fraction of 1.5%. This heterogeneous microstructure endowed the alloy with superior strength and work-hardening capacity compared to the carbon-free alloy. The yield and tensile strengths reached 500 MPa and 979 MPa, respectively, while maintaining a uniform elongation of 42%. This study not only identifies the origin of strengthening and micromechanism of plastic deformation in the carbon-alloyed dual-heterostructured alloy but also elucidates the formation of the specified microstructure. The findings provide theoretical guidance for developing advanced alloys with both high strength and good ductility.