Formation of printing defects and their effects on mechanical properties of additively manufactured metal alloys

Printing defects are known to degrade the performance of additively manufactured (AM) alloys. Thus, a thorough understanding of their formation mechanisms and effects on the mechanical properties of AM materials is critically needed. Here, we take CoCrFeNi high-entropy alloy as a model material and print this alloy by laser powder bed fusion over a wide range of printing conditions. We reveal the processing windows for the formation of different printing defects including lack of fusion (LOF), keyhole, and solidification cracking. LOF and keyholes can be well correlated with insufficient and excessive laser energy density inputs, respectively. Of particular interest, we observe that solidification cracks only emerge at the medium laser energy density region, where the porosity is minimal yet the grain size and misorientation are relatively large. Such observation is rationalized within the framework of Rappaz–Drezet–Gremaud solidification theory. Among the above printing defects, solidification cracks in AM CoCrFeNi result in less degradation of mechanical properties compared with LOF and keyholes due to their different defect densities and resultant capabilities of coalescence. Our work provides fundamental insight into understanding the physical origins underlying the formation of printing defects and their impacts on the mechanical properties of AM metals and alloys.