Mechanical properties, corrosion resistance, and corresponding mechanisms of FeCoCrNiMox high-entropy alloys through regulation of the σ phase

This study investigates the effects of Mo content on FeCoCrNiMo x (x=0, 0.2, 0.5, 0.8) high-entropy alloys fabricated via plasma arc powder-directed energy deposition (PAP-DED). All alloys primarily consist of FCC solid solutions, with σ-phase precipitation increasing with Mo content. Mo addition refines grains and boosts dislocation density up to 2.5×. The alloy with x = 0.2 exhibits optimal performance: yield strength (384 ± 11 MPa), tensile strength (722 ± 12 MPa), and elongation (42.8 ± 2.7%), with strength 2.2–2.3× higher than the Mo-free alloy. Strengthening is dominated by dislocation and precipitation mechanisms. Mo 0 . 2 also shows the best corrosion resistance due to Cr-Mo-O protective oxides. Excessive Mo (x = 0.8) degrades both corrosion resistance and mechanical properties due to σ-phase formation, despite enhancing hardness and wear resistance. Wear shifts from abrasive-adhesive to mainly abrasive. This work clarifies strengthening and corrosion mechanisms under PAP-DED, guiding alloy design for additive manufacturing.