Electron-Beam Powder Bed Fusion of High-Carbon Co-Cr-Mo Alloys for Industrial Applications

In this study, through electron-beam powder bed fusion additive manufacturing, we prepared Co–27Cr–6Mo (wt.%) alloys with different C concentrations up to the eutectic composition (~2.5 wt.%). The Rockwell hardness of the as-built alloy specimens increased linearly with an increase in the carbon concentration, reaching approximately 60 HRC at 2.5 wt.% C. The as-built 2.5C alloy contained a fine carbide network consisting of M7C3- and M23C6-type carbide phases. Increasing the carbon concentration not only increased the carbide fraction and changed the carbide phases but also altered the solidification behavior from cellular at low carbon concentrations to dendritic and finally to eutectic. Quantitative X-ray tomography revealed that carbon addition also affected the gas pore behavior in the melt pool, significantly reducing the porosity when a flat solid/liquid front existed upon solidification (i.e., planar and eutectic). The developed high-carbon alloys cannot be obtained through conventional metal processing; hence, this study opens new avenues for industrial applications of additive manufacturing.