Deformation and strengthening mechanisms in finely heterostructured AlCoCrFeNi2.1 eutectic high-entropy alloys with enhanced strength and ductility

AlCoCrFeNi 2.1 eutectic high-entropy alloys (EHEAs) with a fine heterogeneous microstructure exhibit improved strength-ductility synergy, compared with their coarse counterparts. However, the correlations between complex heterostructures and their properties are not yet fully understood. Here, we investigated the deformation and strengthening mechanisms of AlCoCrFeNi 2.1 EHEAs, including mesoscale plastic deformation behavior, dislocation-nanoprecipitate interactions, and hetero-deformation induced (HDI) hardening. Structurally, the AlCoCrFeNi 2.1 EHEAs have a fine, hierarchically heterogeneous microstructure resulting from rapid solidification processing. The microstructure features eutectic colonies at the microscale, alternating ductile face-centered cubic (FCC) and hard body-centered cubic (BCC) phases at the submicron scale, and nanoprecipitates dispersed within both the FCC and BCC phases at the nanoscale. The unique microstructure is associated with complex and coordinated deformation mechanisms, which respond to the enhanced strength-ductility synergy. The diversely oriented BCC phases within eutectic colonies, which exhibit cellular or spherical morphologies, facilitate slip transmission, promoting compatible deformation between the FCC and BCC phases. Additionally, semicoherent FCC-structured nanoprecipitates within the BCC matrix enhance deformability through dislocation-nanoprecipitate interactions. The microstructural refinement and dense grain boundaries contribute to a more uniform stress and strain distribution, improving work hardening. BCC-structured nanoprecipitates coherent with the FCC matrix provide extra strengthening, whereas the hierarchically heterogeneous microstructure provides mesoscale/microscale HDI hardening. Collectively, these multiscale mechanisms contribute to the strength-ductility synergy in fine heterogeneous EHEAs.