Controlled Parametric Forcing During Directional Solidification of a Bulk Organic Alloy Under Microgravity

F L Mota; K Ji; Y Song; L Littles; A Karma; N Bergeon

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NASA NTRS · 20260007842

Controlled Parametric Forcing During Directional Solidification of a Bulk Organic Alloy Under Microgravity

F L Mota·K Ji·Y Song·L Littles·A Karma·N Bergeon

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Abstract

The response of dendritic microstructures to step-like pulling velocity conditions is investigated using microgravity directional solidification experiments conducted on DECLIC-DSI combined with phase-field simulations. Under a constant pulling velocity of 1.5 µm/s, the evolution toward steady-state growth is characterized in terms of primary spacing, dendrite drift, and tip dynamics. For the first time, side-view observations enabled direct measurement of tip radius and sidebranching frequency. When step-like oscillations of the pulling velocity are imposed, the dendritic array exhibits a strongly period-dependent response: short periods lead to rapid tip adaptation, whereas longer periods induce a phase lag between tip position and morphology, resulting in progressive tip flattening and, above a critical period, interface destabilization and dendrite splitting. Quantitative phase-field simulations, including a realistic thermal field and stochastic noise, reproduce the experimental observations and provide insight into the governing mechanisms, highlighting the role of characteristic relaxation times, sequence-dependent effects, and the irreversible reorganization of the microstructure following splitting.

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Microgravity Transient Solidification Transparent Model Systems Alloy Directional Solidification

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F L Mota, K Ji, Y Song, L Littles, A Karma, N Bergeon. 2026-08-12. Controlled Parametric Forcing During Directional Solidification of a Bulk Organic Alloy Under Microgravity. https://ntrs.nasa.gov/citations/20260007842

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