Abstract
The processes controlling the morphology of dendrites have been of great interest to a wide range of communities, since they are examples of an out-of-equilibrium pattern forming system, there is a clear connection with battery failure processes, and their morphology sets the properties of many metallic alloys. We determine the three-dimensional morphology of free growing metallic dendrites using a novel X-ray tomographic technique that improves the temporal resolution by more than an order of magnitude compared to conventional techniques. These measurements show that the growth morphology of metallic dendrites is surprisingly different from that seen in model systems, the morphology is not self-similar with distance back from the tip, and that this morphology can have an unexpectedly strong influence on solute segregation in castings. These experiments also provide benchmark data that can be used to validate simulations of free dendritic growth.
Highlights
IntroductionWe show through X-ray synchrotron radiation and a novel tomographic reconstruction algorithm that it is possible to image and quantitatively analyze the 3D morphology of growing dendrites during the free-growth stage
Critically important free-growth stage is completely unstudied
Efforts aimed at reducing the time required to collect a dataset have resulted in scan times of as little as 0.15 seconds[18]; this temporal resolution comes at the expense of spatial resolution and the resulting data are too coarsely resolved to make out the details of the dendritic morphology
Summary
We show through X-ray synchrotron radiation and a novel tomographic reconstruction algorithm that it is possible to image and quantitatively analyze the 3D morphology of growing dendrites during the free-growth stage. There are many theoretical predictions of the shape[12] and branching behavior[13,14] of free-growing dendrites and with improvements in computational speed and algorithms, three-dimensional simulations of dendritic growth are on the verge of being possible[15]. We achieve the necessary spatial and temporal resolution improvements by using the time-interlaced model-based iterative reconstruction (TIMBIR) methodology see supplementary information and[19,20]. This was done at the 2-BM beamline at Argonne National Laboratory’s Advanced Photon Source. Because the dendrite growth dynamics during the free-growth stage are diffusion limited, the cooling rate does not have a critical influence on the dendrite morphology or growth behavior
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