Understanding Reactive Inoculation in Laser Powder Bed Fusion: Insights From Advanced Characterization and Modeling
Speaker
Adriana Eres-Castellanos
Postdoctoral Research Associate, Sigma Division, Los Alamos National Laboratory
About This Talk
Additive manufacturing (AM) has unlocked new opportunities for novel part geometries and advanced applications. However, the high thermal gradients (G) inherent to the AM process often promote the formation of undesirable columnar grains. Reactive inoculation has been recently explored as a way to induce grain refinement, preventing solidification cracking and columnar growth. Despite its potential, the mechanisms underlying grain refinement through reactive inoculation are still under investigation.
In this work, Ta-inoculated Al powder was used to conduct simulated laser powder bed fusion (LPBF) experiments with in-situ radiography at the Advanced Photon Source (Argonne National Laboratory). During solidification, Ta nanoparticles were expected to dissolve into molten Al and form Al3Ta precipitates, acting as nucleation sites for equiaxed grains.
Electron Backscattered Diffraction (EBSD) analysis of the resulting melt pool microstructures revealed heterogeneous grain refinement, the origins of which were not immediately evident. To investigate the factors contributing to this heterogeneity, solidification velocities (V) were measured directly from in-situ radiography, while thermal gradients (G) were modeled using Computational Fluid Dynamics (CFD). However, G-V conditions alone did not fully explain the observed variations.
Further characterization using Scanning-Transmission Electron Microscopy (STEM) and TEM-based crystallographic mapping revealed partial Ta dissolution, oxide formation and particle agglomeration, supported by coupled CFD and thermodynamics modeling. Quantitative metallography showed no strong correlation between particle size/density and thermal profiles in the analyzed regions. Nucleation potency and grain initiation were evaluated through solidification theory.
These findings emphasize complex physical interactions involved in reactive inoculation, highlighting the need to consider coupled effects of multiple factors, thermal gradients, fluid dynamics, and particle motion, to achieve effective and homogenous grain refinement in AM processes.
About the Speaker
Adriana Eres-Castellanos is a Postdoctoral Research Associate in the Sigma Division at Los Alamos National Laboratory. Her academic interests encompass physical metallurgy, with a particular emphasis on texture/crystallography, processing-microstructure relationships, and the investigation of fundamental physical mechanisms governing solidification and solid-state phase transformations in metals subjected to additive manufacturing (AM). Her research integrates experimental studies, including AM processing and microscopy, with modeling of simulated AM conditions by Computational Fluid Dynamics (CFD), across various alloy systems.
Eres-Castellanos earned her PhD in Materials Science from Menendez Pelayo International University (Spain), where she specialized in thermo-mechanical processes and the crystallography of displacive phase transformations in medium-carbon steels. During her postdoctoral stage at Colorado School of Mines, she investigated solidification in model alloys under simulated AM conditions. She is now extending that knowledge to a wider range of alloys and AM processes at LANL.