3 research outputs found
Grain coarsening in two-dimensional phase-field models with an orientation field
In the literature, contradictory results have been published regarding the
form of the limiting (long-time) grain size distribution (LGSD) that
characterizes the late stage grain coarsening in two-dimensional and
quasi-two-dimensional polycrystalline systems. While experiments and the
phase-field crystal (PFC) model (a simple dynamical density functional theory)
indicate a lognormal distribution, other works including theoretical studies
based on conventional phase-field simulations that rely on coarse grained
fields, like the multi-phase-field (MPF) and orientation field (OF) models,
yield significantly different distributions. In a recent work, we have shown
that the coarse grained phase-field models (whether MPF or OF) yield very
similar limiting size distributions that seem to differ from the theoretical
predictions. Herein, we revisit this problem, and demonstrate in the case of OF
models [by R. Kobayashi et al., Physica D 140, 141 (2000) and H. Henry et al.
Phys. Rev. B 86, 054117 (2012)] that an insufficient resolution of the small
angle grain boundaries leads to a lognormal distribution close to those seen in
the experiments and the molecular scale PFC simulations. Our work indicates,
furthermore, that the LGSD is critically sensitive to the details of the
evaluation process, and raises the possibility that the differences among the
LGSD results from different sources may originate from differences in the
detection of small angle grain boundaries
Orientation-field models for polycrystalline solidification: grain coarsening and complex growth forms
We compare two versions of the phase-field theory for polycrystalline solidification, both relying on the concept of orientation
fields: one by Kobayashi et al. [Physica D 140 (2000) 141] and the other by Henry et al. [Phys. Rev. B 86 (2012) 054117]. Setting
the model parameters so that the grain boundary energies and the time scale of grain growth are comparable in the two models, we
first study the grain coarsening process including the limiting grain size distribution, and compare the results to those from experiments
on thin films, to the models of Hillert, and Mullins, and to predictions by multiphase-field theories. Next, following earlier
work by Gránásy et al. [Phys. Rev. Lett. 88 (2002) 206105; Phys. Rev. E 72 (2005) 011605], we extend the orientation field to the
liquid state, where the orientation field is made to fluctuate in time and space, and employ the model for describing of multi-dendritic
solidification, and polycrystalline growth, including the formation of “dizzy” dendrites disordered via the interaction with foreign
particles
Phase-field modeling of polycrystalline solidification, from needle crystals to spherulites: a review
Advances in the orientation-field-based phase-field (PF) models made in the past are reviewed.
The models applied incorporate homogeneous and heterogeneous nucleation of growth centers
and several mechanisms to form new grains at the perimeter of growing crystals, a phenomenon
termed growth front nucleation. Examples for PF modeling of such complex polycrystalline
structures are shown as impinging symmetric dendrites, polycrystalline growth forms (ranging
from disordered dendrites to spherulitic patterns), and various eutectic structures, including
spiraling two-phase dendrites. Simulations exploring possible control of solidification patterns
in thin films via external fields, confined geometry, particle additives, scratching/piercing the
films, etc. are also displayed. Advantages, problems, and possible solutions associated with
quantitative PF simulations are discussed briefly