Impact of build orientation on multi-material Laser Beam Powder Bed Fusion
Researchers from Pennsylvania State University, University Park, Pennsylvania, USA, recently published a paper in npj Advanced Manufacturing which analyses the impact of build orientation as a contributing factor to material compatibility, process-induced defects, and interfacial formation mechanisms of multi-material parts produced via Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing.
This study also demonstrated multi-material PBF-LB capabilities through a complex gyroid structure (904L stainless steel and bronze) for unique signatures (e.g., melt pool characteristics, grain morphology, defects, and mechanical properties). Fracture mechanisms in PBF-LB are investigated through multi-scale domain techniques, including flexural testing supported by digital image correlation (DIC), finite element analysis (FEA), and intermittent micro-CT.
While multi-material PBF-LB enables the creation of complex, multifunctional components, the knowledge of how to process single-material components must be scaled to account for interaction.
The researchers highlighted the following discoveries as the most noteworthy:
- Defects and melt-pool morphology observed at the interface of parts additively manufactured via PBF-LB are shown to be highly dependent on material orientation with respect to the build direction
- Part orientation, with respect to the recoating direction, does not have a significant impact on interfacial defects, especially when compared to the build direction
- Rapid solidification, Marangoni convection and the ‘dilution’ effect are the main mechanisms behind elemental diffusion within the interface
- Multi-scale cracking, which occurs solely within the 904 L SS region adjacent to the interfacial plane are attributed to a mismatch in thermophysical properties, and grain boundary solute segregation
- Grain boundary solute segregation in regions containing high ratios of steel to bronze will promote crack-initiating sites to form under solidification and thermal strain loading, leading to regional solidification cracking; good metallurgical bonding is more likely to occur in regions with balanced mixing of steel and bronze, where the volume fraction of bronze is sufficient to backfill these initiating sites
- The mechanical testing of complex TPMS structures reveals premature failure which originates from nano- and micron-scale cracking near the interface, when compared to FEA simulation
‘Multi-material laser powder bed fusion: effects of build orientation on defects, material structure and mechanical properties’ is available here.
