Abstract
Homogeneous nucleation from aluminum (Al) melt was investigated by million-atom molecular dynamics simulations utilizing the second nearest neighbor modified embedded atom method potentials. The natural spontaneous homogenous nucleation from the Al melt was produced without any influence of pressure, free surface effects and impurities. Initially isothermal crystal nucleation from undercooled melt was studied at different constant temperatures, and later superheated Al melt was quenched with different cooling rates. The crystal structure of nuclei, critical nucleus size, critical temperature for homogenous nucleation, induction time, and nucleation rate were determined. The quenching simulations clearly revealed three temperature regimes: sub-critical nucleation, super-critical nucleation, and solid-state grain growth regimes. The main crystalline phase was identified as face-centered cubic, but a hexagonal close-packed (hcp) and an amorphous solid phase were also detected. The hcp phase was created due to the formation of stacking faults during solidification of Al melt. By slowing down the cooling rate, the volume fraction of hcp and amorphous phases decreased. After the box was completely solid, grain growth was simulated and the grain growth exponent was determined for different annealing temperatures.
Highlights
In metal manufacturing processes involving solidification, the crystal nucleation from the melt controls the formation and growth of nano- and micro-structures of metals
We demonstrated the capability of 2NN modified embedded atom method (MEAM) potentials in predicting solid-liquid coexistence properties of Fe 40, 41, Ni, Cu, Al 23, and Mg 42, such as melting point, latent heat, expansion in melting, liquid structure factor, and solid–liquid interface free energy and anisotropy. 2NN MEAM potential can reliably predict room-temperature properties, such as elastic constants, surface energies, vacancy formation energy, and stacking fault energy
We studied the homogenous crystal nucleation from Al melt by molecular dynamics (MD) simulations utilizing the second nearest-neighbor modified embedded atomic method (2NN MEAM) interatomic potential of Al 43
Summary
In metal manufacturing processes involving solidification (e.g., casting 1 , welding 2, and laser additive manufacturing 3), the crystal nucleation from the melt controls the formation and growth of nano- and micro-structures of metals. Ѕ Ą 瑹怴μ咊 cleation rates in crystallization from the melt cannot provide reliable tests of the classical nucleation theory (CNT) 13, 14 Another fundamental problem with homogenous nucleation experiments, especially for metallic materials, is that it is difficult to purify a liquid to exclude Halol mthoegiemnpouursitnieusctlheaatticoannfcraotmalymzeetnaullcicleamtieolnts15i,s16a. To reliably study the crystal nucleation process from melt by MD simulations, the interatomic potentials used for MD simulations of solidification need to accurately predict the behavior of solid-liquid interfaces. There is only one work which used MD simulations 28 to study solidification of Al. this study doesn’t provide quantitative analysis on nucleation, critical nucleus formation, induction time, comparison of MD results to CNT, or details on solid state grain growth. We studied the homogenous crystal nucleation from Al melt by MD simulations utilizing the second nearest-neighbor modified embedded atomic method (2NN MEAM) interatomic potential of Al 43. In the last section we provide detailed analysis of the solidstate grain growth mechanism of pure Al after solidification
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