Effect of energy density on defect evolution in 3D printed Zr-based metallic glasses by selective laser melting

In this study, the defects in 3D printed Zr-based bulk metallic glasses (BMGs) fabricated by selective laser melting (SLM) under different energy densities have been investigated via both experimental and simulation approaches. Different defects, including balling, interlayer pores, open pores and metallurgical pores, are detected in the 3D-printed Zr-based MGs depending on the energy inputs. Balling mainly occurs at a relatively low energy density (E 8.33 J/mm(3)) due to the incomplete melting of particles, while interlayer pores and open pores are formed at modest energy densities (E=13.89-16.67 J/mm(3)) because of incomplete welding and insufficient filling of molten liquid between layers. Fine metallurgical pores appear on the upper surface at relatively high energy densities (E=20.83-27.78 J/mm(3)), which originate from gas escaping from molten pools during rapid solidification of the melt. Computational fluid dynamics (CFD) simulations are carried out to verify the experimental observations. The CFD simulations reveal that the various defects formed in the 3D-printed Zr-based BMG are related to the melt flow behaviours in the molten pools under different energy densities. The present work provides in-depth understandings of defect formation in the SLM process and provides methods for eliminating these defects in order to enhance the mechanical performance of 3D printed BMGs.