Capillary-mediated solid-liquid energy fields: Their detection with phase-field method

Observations of melting crystallites in microgravity showed unusual shape changes as melting proceeded toward extinction. When re-analyzed in 2011, shape evolution data showed needle-like crystallites becoming spheroids as they melted toward extinction, suggesting that some type of capillary phenomenon at solid-liquid interfaces was responsible for an energy release capable of spherodising particles on melting, and stimulating pattern formation during unstable crystal growth. The presence of these previously undetected energy fields was recently uncovered using phase-field simulations that employ an entropy density functional. Simulations allow measurement of interfacial energy distributions on equilibrated solid-liquid interfaces configured as stationary grain boundary grooves (GBGs). Interfacial energy source fields - related to gradients in the Gibbs-Thomson temperature - entail persistent cooling along GBG profiles, a new result that fully confirms earlier predictions based on sharp-interface thermodynamics. This study also provides new insights to improve microstructure control at reduced scales by explaining the thermodynamic fields responsible for pattern formation in castings.