Influence of Build Strategy on Unmelted Powder Particles in Refractory Multi-Principal Element Alloys Fabricated via Directed Energy Deposition-Laser Beam

Abstract Refractory multi-principal element alloys (RMPEAs) have significant high-temperature strength making them suitable for elevated-temperature applications. With the advent of additive manufacturing (AM) and particularly directed energy deposition-laser beam (DED-LB), fabrication of large scale RMPEA parts with various compositions has become possible. However, unmelted powder particles are frequently observed in the AM fabrication of these alloys, which would cause poor mechanical properties and can act as regions of crack initiation. This work aims to quantify and understand the presence of unmelted particles, as affected by build sequence, for a W-25 wt.% Ta-25 wt.% Re alloy. For fixed process parameters, the number density of unmelted W particles decreases with increasing print order, consistent with the effect of heat build-up in the build plate. A simple mass transfer-based model predicted dissolution times that are similar to melt-pool lifetime, which suggests that strategies that would increase the melt-pool lifetime, such as changing the heat input or controlling heat build-up, will ensure full dissolution.