Heterogeneous nucleation of solid Al from the melt byTiB2andAl3Ti: Anab initiomolecular dynamics study

Abstract

The nucleation of solid Al from the melt by TiB 2 is well established and is believed to involve the formation of Al 3 Ti. Since the atomic scale mechanisms involved are not fully understood, we look to computer simulation to provide insight. As there is an absence of suitable potentials for all of this complex system we have performed large scale density functional theory molecular dynamics simulations of the nucleation of solid Al from the melt on TiB 2 and Al 3 Ti substrates at undercoolings of around 2K. Using periodic boundary conditions, we find limited ordering and no signs of incipient growth in the liquid Al close to the B-terminated surface of TiB 2 . By contrast, we see fcc-like ordering near the Ti-terminated surface, with growth being frustrated by the lattice mismatch between bulk Al and the TiB 2 substrate. The Al interatomic distances at the Ti-terminated surface are similar to distances found in Al 3 Ti; we suggest that the layer encasing TiB 2 observed experimentally may be strained Al on a Ti-terminated surface rather than Al 3 Ti. For the Al 3 Ti substrate, fcc-like structures are observed on both sides which extend rapidly into the melt. Periodic boundaries introduce unphysical stresses which we removed by introducing a vacuum region to separate the liquid from the solid at one of the interfaces. We see ordering in the Al on both the B-terminated (0001) surface of TiB 2 , and on Al 3 Ti(112), with the ordering able to be stronger on the Al 3 Ti substrate.However, we cannot draw strong conclusions as these simulations need more time to allow long ranged fluctuations in the liquid Al to dampen out. The huge computational cost restricted the range and duration of simulations that was possible.

Orientation dependences of the Fe-Li solid-liquid interface properties: Atomistic simulations

“…The results showed that the liquid Li atoms near the interface were layered, during the simulation duration few Li atoms invaded into the Fe substrate even at 1100K, and also few Fe atoms dissolved in the liquid Li. Previous literatures reported that the interface properties present apparent orientation dependences [10][11][13][14][15][16][17][18], which suggests that to obtain a full view of the interface properties of the Fe-Li solid-liquid interface further work should be done. In this work, the Fe(110)/(111)-Li solid-liquid interfaces are examined and the results are compared with each other as well as with our previous findings, what's more we have illuminated the underlying mechanism of the orientation dependence observed in the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT interface properties.…”

“…Very recently, Turlo et al [3] simulated the dissolution process of solid Ni in liquid Al and a diffusion-limited dissolution model has been developed. In order to unveil the grain refining mechanism of Al with different refiners, the interfaces between refiners and liquid Al have been extensively investigated [15][16][17][18][19]. The findings have exposed different refining mechanisms of different refiners and the different refining abilities of different crystal planes.…”

Substrate-Induced Liquid Layering: A New Insight into the Heterogeneous Nucleation of Liquid Metals

“…The initial S/L interfacial models for the simulations were prepared using the method proposed by Wang et al [12]. In the first step, the solid substrates were fully relaxed, until the residual forces fell below 0.01 eV/Å; meanwhile, liquid Al was prepared by melting the solid Al (15 × 15 × 15 supercell) in Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [43] using the embedded atom model (EAM) potential [44].…”

“…These ordered structures may manifest as clusters with unique symmetry (such as the well-assumed icosahedral structure [3]) or quasi-layers [4][5][6][7][8][9]. The former mainly occur in the systems absence of inoculation [3] and the latter have frequently been observed near the atomically smooth surfaces [10][11][12][13]. In this work, we focus on the substrate-induced liquid layers, which have been extensively studied in the field of lubrication, epitaxial growth, superhydrophobic materials [6], energy-storage materials [8,14], etc.…”

First-principles calculation of Mg/MgO interfacial free energies

“…The combination of DFT and MD is especially appealing as it allows us to retain an accurate description of the cohesion while including the nuclear dynamics associated with finite temperatures [21,22]. However, it is a computationally expensive approach and for many cases less costly alternatives are necessary.…”