Formation and Evolution of Metastable bcc Phase during Solidification of Liquid Ag: A Molecular Dynamics Simulation Study

Abstract

On the basis of the quantum Sutton-Chen potential, the rapid solidification processes of liquid silver have been studied by molecular dynamics simulation for four cooling rates. By means of several analysis methods, the competitions and transitions between microstructures during the cooling processes have been analyzed intensively. It is found that there are two phase transitions in all simulation processes. The first one is from liquid state to metastable (transitional) body-centered cubic (bcc) phase. The initial crystallization temperature T(ic) increases with the decrease of the cooling rate. The second one is from the transitional bcc phase to the final solid phase. This study validates the Ostwald's step rule and provides evidence for the prediction that the metastable bcc phase forms first from liquid. Further analyses reveal that the final solid at 273 K can be a mixture of hexagonal close-packed (hcp) and face-centered cubic (fcc) microstructures with various proportions of the two, and the slower the cooling rate is, the higher proportion the fcc structure occupies.

Surface segregation of bimetallic alloys in nanoscale confinement

“…11 The QSC includes quantum corrections and takes into account the zero point energy, allowing for better prediction of temperature-dependent properties and, in particular, of the phase transformation of fcc alloys. [12][13][14] The relatively weak carbon-metal interaction is modeled by pairwise Lennard-Jones ͑LJ͒ potentials, with energy and distance parameters obtained from the geometric and arithmetic mean, respectively, of the corresponding LJ parameters for graphite 15 and the considered metal. 16 Metalmetal interactions and van der Waals forces were both truncated at 10 Å.…”

Structural evolution in the crystallization of rapid cooling silver melt

“…The first method is based on the Pair Distribution Function (PDF or g(r)) which examines one-dimensional (1D) structure (of paired atoms). The validity of this simulation has been established by comparing the simulated and measured g(r) in the previous study [19]. The second method is based on the Angular Distribution Function (ADF) related to three-body (two-dimensional (2D) structure) correlation [40,41], providing a type of overall information about the phase transition, such as the symmetry of microstructures.…”

“…For example, a simulation for a 10 6 -particle L-J system reported that the bcc structures form prior to fcc/hcp ones in a cooling process, with its amount being so small that it is believed to play a very limited role in crystallization [18]. On the other hand, the recent MD simulations for silver melt demonstrate that an intermediate bcc phase is indeed the precursor of the final fcc crystal [19], but for such a small system (only containing 500 atoms) the scale effect is inevitable. Therefore, it is necessary to further investigate the role of the metastable bcc structures during crystallization of metals.…”

A method for structural analysis of disordered particle systems

“…Therefore, cluster scale analysis methods, where a particle and its neighbours are considered together, are proposed and show better capacity of distinguishing different local structures. The methods proposed thus far include (HoneycuttAnderson) HA-Pair, CNA (common near analysis), and BCA (basic cluster analysis) [8][9][10][11]. The effectiveness of these methods, however, is quite sensitive to a pre-set cut-off distance r c , resulting in uncertainty in structural quantification.…”