Tailoring the strengthening mechanisms of high-entropy alloys toward excellent strength-ductility synergy by metalloid silicon alloying: A review

Metalloids and transition/refractory elements typically differ significantly in the electronic structure and atomic size, allowing for stronger solid-solution hardening in high-entropy alloys (HEAs) as well as improved work-hardening capability, which leads to exceptional strength-ductility synergy. In this regard, Si addition has opened up a new pathway for developing novel and high-performance HEAs, which has recently attracted considerable attention from the materials science community. Accordingly, the present review paper summarizes the recent progress in tailoring the mechanical properties and strengthening mechanisms of Si-added HEAs. After reviewing the general strengthening mechanisms of HEAs, the impact of Si addition is critically discussed, especially its effects on the (I) solid-solution hardening by local lattice distortion and chemical short-range order hardening, (II) second-phase strengthening by promoting the formation of disordered solid-solution phases, silicides, σ-phase, and other intermetallics, (III) structural refinement and facilitating the development of heterostructures, and (IV) work-hardening behavior by altering the dislocation arrangements, boosting the twinning-induced plasticity (TWIP) effect as well as HCP and BCC transformation-induced plasticity (TRIP) effect by reduced and variable stacking fault energy (SFE). Finally, the research gaps and future prospects are introduced, including metastability engineering, superplasticity, application of severe plastic deformation (SPD) techniques, and additive manufacturing.