Effect of partial substitution of Cr with Co on the properties of Fe35Ni20Cr20-xCoxMo5P12C4B4 high-entropy bulk metallic glasses

Novel Fe ₃₅Ni ₂₀Cr _20-xCo _xMo ₅P ₁₂C ₄B ₄ ( x = 0, 4,8, 12, 16 in at.%, denoted as Cr _20-xCo _xMo ₅) high-entropy bulk metallic glasses (HE-BMGs) with excellent comprehensive performance were successfully fabricated using Fluxing and J-quenching methods. The focus was on studying the influences of different Co content on the glass-forming ability (GFA), mechanical performances, magnetic properties, and anti-corrosion performance. It was found that adding an appropriate amount of Co to replace Cr in Cr _20-xCo _xMo ₅ alloys can improve GFA. The Cr ₁₂Co ₈Mo ₅ specimen displays the maximum critical diameter of 3.5 mm and maximum super-cooled liquid phase of 51 K. The compression tests show that the plasticity was enhanced from 0.2 % for the Co-free alloy to 2.5 % for the 12 at.% Co-added alloy. The saturation magnetization ( J _s) of Cr _20-xCo _xMo ₅ alloys gradually increased from 0.04 to 0.68 T with the increase of Co. Electrochemical tests indicate that in 3.5 wt.% NaCl solution at room-temperature (RT), the anti-corrosion performance of Cr _20-xCo _xMo ₅ alloys expresses a trend of first increasing and then decreasing with the increase of Co, and all samples show a remarkably higher anti-corrosion performance than 316 L and 304 L stainless steel. The Cr ₁₆Co ₄Mo ₅ sample exhibits the highest anti-corrosion performance with the self-corrosion current density ( I _corr) and the self-corrosion potential ( E _corr) are 9.5 × 10 ⁻⁹ A/cm ² and -0.270 V, respectively. The X-ray photoelectron spectroscopy (XPS) analysis of the Cr ₁₆Co ₄Mo ₅ shows that there is a higher content of metal kation oxides of Fe ²⁺, Cr ³⁺ and Mo ⁴⁺ in the passive films compared to Cr ₂₀Mo ₅ and Cr ₄Co ₁₆Mo ₅. It is indicated that the Cr ₁₆Co ₄Mo ₅ specimen has the optimal corrosion resistance in this current research. The present HE-BMGs have high GFA, high plastic strain,and excellent anti-corrosion performance, which have potential application value in the engineering field.