Microstructure and mechanical properties of novel Si-added CrFeNi medium-entropy alloy prepared via vacuum arc-melting

•A series of novel Co-free CrFeNiSix MEAs was prepared via vacuum arc-melting.•Si induced the formation of (Cr, Si)-rich σ phase in CrFeNiSix MEAs.•The growth accident model was the main formation mechanism of Σ3 boundaries.•The increasing σ phase resulted in the transformation of fracture mechanisms.•There is a good trade-off between strength and ductility in CrFeNiSi0.15 alloy.