As-Solidified Microstructures from Powder Bed Fusion
Powder bed fusion (PBF) is one of the most popular techniques in additive manufacturing, in which a laser or other heat source is repeatedly scanned across a bed of powdered feedstock material in a layer-by-layer fashion. In printed alloys, the developed microstructure is different than in cast components, as grains often grow epitaxially from existing grains in the powder or previous layers. As more material is printed, the grains can branch as additional favorable orientations are exposed.
We have developed a polycrystalline phase-field model that tracks the solidification and competitive growth of thousands of grains as they interact with a moving melt pool. With the model, we can examine how kinetic anisotropy, the grain size distribution of the powder and baseplate, the melt pool geometry, and the scan strategy all interact to influence the final microstructure. The model can also consider solidification and grain growth across multiple powder layers. In tandem, we have derived a set of analytical models that consider how trijunctions traverse the melt pool under equilibrium conditions. These latter models serve to verify the phase-field model and also reveal the dramatic role that the melt pool geometry plays in the microstructural evolution. The overall modeling framework will lead to improved understanding of how microstructure and texture develop during printing, which can then inform other multiscale modeling tools as part of a predictive ICME approach.
Participants
Publications
A. F. Chadwick and P. W. Voorhees, “The Development of Grain Structure During Additive Manufacturing,” Acta Materialia, (2021) doi: 10.1016/j.actamat.2021.116862
A. F. Chadwick and P. W. Voorhees, “Recursive grain remapping scheme for phase-field models of additive manufacturing,” International Journal for Numerical Methods in Engineering, (2022) doi: 10.1002/nme.6966
Figure Description: Predicted solidification of a polycrystalline 316L stainless steel baseplate with mild kinetic anisotropy and a Rosenthal thermal solution. A characteristic “palm frond” morphology develops that is disrupted at the center of the laser track due to competitive grain growth and the anisotropy.