Synergistic solid-solution and silicide strengthening in Si-modified MoNbVTa 0.5 refractory high entropy alloy

Systematic investigation into the impact of Si additives on the development of phases, mechanical performance, and corrosion behaviour of MoNbVTa0.5Six (x = 0–0.75) refractory high-entropy alloys. The XRD analysis showed that the alloy without Si exhibits a single-phase BCC structure, while the Si-containing compositions show a coexistence of the BCC phase and an M₅Si₃-type silicide phase. The gradual change in the BCC peaks to higher 2θ values confirmed that the lattice was contracted as the Si content increased. Microhardness had a significant increase between 488 HV (x = 0) and 954 HV (x = 0.75). At room temperature, compressive testing revealed that there was a high degree of strengthening. Electrochemical measurement of 3.5 wt.% NaCl solution indicated increased corrosion resistance, with the corrosion potential shifting from −0.372 V to −0.242 V. The enhanced performance is attributed to combined solid-solution strengthening, silicide precipitation and the formation of stable protective oxide films.