Enhanced strength-ductility synergy by high density heterogeneous precipitation microstructure in high-entropy alloys

Heterogeneous microstructures have become a crucial method for high-entropy alloys (HEAs) to overcome the limitations of strength and plasticity synergy, as well as to explore other unique material properties or novel materials. Here, a strategy has been reported for breaking the strength-ductility trade-off by introducing non-metallic element Si in Fe₅₅Co₁₅Cr₁₀Al₈Ni_12-xSi_x (x = 0, 3 at. %) alloys system. The microstructure evolution and its effect on the mechanical properties were systematically analyzed and discussed. The results suggested that the addition of Si elements facilitates the transformation of the face-centered cubic (FCC) into body-centered cubic (BCC) microstructures, in which the spherical Al, Ni-rich B2 nanoparticles are coherently dispersed in the Fe, Cr-rich BCC matrix. Namely, the microstructure of HEA devoid of the Si element exhibits FCC + BCC dual-phase heterogeneous structures, while the microstructure evolves into a BCC-based B2 precipitation heterogeneous structures after adding Si. The B2 precipitates in alloys act as strengtheners that can block dislocation motion thus enhance the work hardening capability to strengthen materials. The heterogeneous precipitation microstructure resulting from Si alloying significantly elevates the mechanical properties of the alloy, which exhibit excellent strength of 1.4 GPa at room temperature with minimal sacrifice in plasticity. This strategy of utilizing B2 precipitation heterogeneous structures provides a promising way for the development of next-generation structural materials.