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

Novel Fe35Ni20Cr20-xCoxMo5P12C4B4 (x = 0, 4,8, 12, 16 in at.%, denoted as Cr20-xCoxMo5) 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 glassforming ability (GFA), mechanical performances, magnetic properties, and anti-corrosion performance. It was found that adding an appropriate amount of Co to replace Cr in Cr20-xCoxMo5 alloys can improve GFA. The Cr12Co8Mo5 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 (Js) of Cr20-xCoxMo5 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 Cr20-xCoxMo5 alloys expresses a trend of first increasing and then decreasing with the increase of Co, and all samples show a remarkably higher anticorrosion performance than 316 L and 304 L stainless steel. The Cr16Co4Mo5 sample exhibits the highest anticorrosion performance with the self-corrosion current density (Icorr) and the self-corrosion potential (Ecorr) are 9.5 x 10-9 A/cm2 and -0.270 V, respectively. The X-ray photoelectron spectroscopy (XPS) analysis of the Cr16Co4Mo5 shows that there is a higher content of metal kation oxides of Fe2+, Cr3+ and Mo4+ in the passive films compared to Cr20Mo5 and Cr4Co16Mo5. It is indicated that the Cr16Co4Mo5 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.