Effect of Mo content on the microstructure and mechanical properties of (CoNi)80-xCr10Fe10Mox multi principal element alloys

In the field of multi-principal element alloys (MPEAs), developing face-centered cubic (FCC) structured alloys with optimized strength-plasticity balance remains a critical challenge. This study systematically explores the impact of Mo content on the microstructure and mechanical properties of (CoNi)_80-xCr₁₀Fe₁₀Mo_x alloys. With increasing Mo content, the alloy changes from a single phase to a dual phase structure. At the same time, the stacking fault energy decreases from 20.25 mJ/m² of C-Mo5 to 19.62 mJ/m² of C-Mo13. After thermomechanical processing, μ phase precipitates along grain boundaries in A-Mo13, which enhances the tensile strength of the alloy. Compared with the single-phase A-Mo9 alloy, the tensile strength of the A-Mo13 alloy increases by 300 MPa, with only an 8% loss in plasticity. The combined strengthening mechanisms primarily include grain refinement and second phase strengthening. Through the synergistic effects of thermo-mechanical treatment and μ-phase precipitation, the FCC grains were refined from 150 μm to 7.4 μm. Simultaneously, as a hard second phase, the Mo-rich phase impedes dislocation movement and alters the crack propagation path, thus improving the tensile strength and maintaining good plasticity. The findings of this study provide valuable theoretical and practical insights for the strengthening of FCC MPEAs.