SUMMARY

Metal additive manufacturing (AM) and the laser powder bed fusion (LPBF) AM process have gained recent prevalence due to their unique capabilities which nullify many design constraints typically encountered in traditional manufacturing processes for metals. However, it has been observed that material defects, often appearing to be unpredictable in their occurrence, can introduce high scatter in the mechanical properties of manufactured workpieces nominally produced under the same process conditions. This lack of process repeatability defies the typical concept of a ‘material lot,’ which implies that materials which share a common manufacturing pedigree should also share similar properties. Through a variety of experimental, numerical, and analytical approaches, this work has studied the precise nature and causal factors of material lot variability. To better understand the origination of material defects, LPBF process signals that contribute to defect formation were measured and analyzed, with a focus on novel measurement approaches for powder bed quality and spatter redistribution. Additionally, the scope and nature of material lot variability in LPBF, particularly as related to fatigue, was quantified and studied. Finally, modeling frameworks capable of predicting material lot variability as a function of process behavior and material defects were developed. Through this work, a more comprehensive understanding of process phenomena formerly treated as unpredictable in nature was attained and causal links between the manufacturing process and material properties were proposed. These results enable progress in process optimization, process monitoring, and manufacturing technology that mitigate high material lot variability, thereby enabling the implementation of LPBF in applications with high reliability requirements.