Applications of Solidification Fundamentals: Simulation and Modeling of Solidification Behavior
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Solidification Committee
Program Organizers: Andre Phillion, McMaster University; Amber Genau, University of Alabama at Birmingham; Lifeng Zhang, University of Science and Technology Beijing

Tuesday 2:00 PM
February 28, 2017
Room: 19
Location: San Diego Convention Ctr

Session Chair: Andre Phillion, McMaster University

2:00 PM  
Investigating Homogenous Nucleation in Solidification of Aluminum and Iron by Molecular Dynamics Simulations: Avik Mahata1; Mohsen Asle Zaeem1; Michael Baskes2; 1Missouri University of Science and Technology; 2University of California, San Diego
    Homogeneous nucleation from an undercooled fcc aluminum and bcc iron melts were investigated by million-atom molecular dynamics simulations utilizing the second nearest neighbor modified embedded atom method interatomic potentials. The natural spontaneous nucleation was reproduced over a very large timescale without any influence of impurity, pressure and surface effects. Three thermodynamic regimes were detected: (I) Nucleation from the liquid: fcc or bcc small particles (initial nuclei) formed, and most of them dissolved back to the liquid phase. (II) Some particles reached the size of a critical nucleus (which was found to be ~0.82 nm for Al and ~0.77 nm for Fe) and passed the barrier of critical radius. (III) After overcoming the critical radius, further growth of particles led to a favorable condition for continuous solidification, and this eventually led to formation of bulk-crystalline solid. fcc aluminum exhibited hcp staking faults while bcc iron did not show any crystalline defects

2:20 PM  
Inoculant Undercooling Induced Nucleation and Growth during Equiaxed Solidification: Effect of Location and Separation Distance of the Inoculants and Time: Arvind Prasad1; Lang Yuan2; Peter Lee3; Mark Easton4; David StJohn1; 1University of Queensland; 2GE; 3University of Manchester; 4RMIT
    The Interdependence Model provides a simple analytical model to predict grain size during equiaxed solidification of a casting. A numerical solidification model, μMatIC, has been used to confirm some of the predictions from the Interdependence Model. This model has been extended so that a value of nucleation undercooling can be assigned to each inoculant particle at specific locations. Inoculants were placed at user-defined locations around a centrally growing grain. The preliminary results from this enhanced model indicate that the centrally growing grain causes a constitutional undercooling field to develop which changes both with time and location. This paper explores the success/failure of inoculants to trigger nucleation events with respect to the position of the user-placed inoculants and the effect of the time-varying undercooling field.

2:40 PM  
Nucleation of Solidification in Confined High Aspect Ratio Films: James Mastandrea1; Joel Ager1; Daryl Chrzan1; 1Lawrence Berkeley National Laboratory
    Thin film growth without nucleation control can lead to grain sizes on the order of or smaller than the film’s thickness; however, for many applications larger grain sizes are desired. Classical nucleation theory is used to consider the solidification of a melt confined between two surfaces. The critical nuclei shapes and the associated nucleation energy barriers are computed as a function of the film’s thickness, and the film's bulk and interface free energies. A diagram is constructed that presents the morphology of the nuclei and the melting points as a function of the system parameters. A possible route for orientation control is identified as confinement of the film can lead to a large range of nucleation temperatures. Thus by controlling the growth temperature, certain orientations may not be able to nucleate thereby reducing the possible number of film orientations. This work was supported by the DOE under contract No. DE-AC02-05CH11231.

3:00 PM  
Thermomechanical Properties of Metals during Solidification by Molecular Dynamics Simulations: Seyed Alireza Etesami1; Ebrahim Asadi1; 1University of Memphis
    Many metal manufacturing processes involve with near the melting processes such as solidification. Computational materials models such as phase-field models can be used to investigate these processes provided near the melting thermomechanical properties. While conducting experiments at those high temperatures is very challenging, molecular dynamic (MD) simulation offers a powerful tool to that end. Here, we present a systematic method to determine thermal linear expansion coefficient, heat capacity, and elastic constants of Fe,Cu,Ni, and Al during solidification using modified embedded-atom method (MEAM) MD simulations. MEAM potentials are developed by considering a wide range of low temperature properties and the melting point of the metal. Due to the huge fluctuations of atoms at high temperatures, the calculation of elastic constants is carried out by a universal, fast deformation–fluctuation hybrid approach which is significantly faster than direct method and results in much smaller standard deviations for the calculated data.

3:20 PM Break

3:40 PM  
On the Transition from Equiaxed Sedimentation to Viscoplastic Packed Bed Dynamics: Andreas Ludwig1; Menghuai Wu2; Christian Rodrigues2; Tobias Holzmann2; Alexander Vakhrushev2; 1Montanuniversitaet Leoben; 2Montanuniversitšt Leoben
    During equiaxed solidification, crystals sediment and form a so called packed bed. The transition from the sedimenting crystals to the packed ones is referred to as coherency point, the stage were individual crystals first impinge their neighbors. The behavior of separated moving crystals can be described by a submerged object approach, whereas the viscoplastic behavior of a semi-solid slurry follows a volume-averaged viscoplastic constitutive equation. The present contribution specially focuses on the transition between the two regimes and discusses the implication that comes from the fact that both approaches decrease in accuracy close to the corresponding border. It is shown that the presumed coherency point can be varied in a certain range without violating either of the two approaches.

4:00 PM  
Lattice Boltzmann GPU Solutions for Alloy Microstructure Development and Solute Transport: Ivars Krastins1; Andrew Kao1; Koulis Pericleous1; 1University of Greenwich
    Solidification of alloy microstructures is of great importance for material processing dictating macroscopic thermo-physical properties. Studies have highlighted the effect that convective heat and mass transport has on dendrite morphology in both free growth and directional solidification. Modelling solutal hydrodynamics during solidification involves the complex geometry of evolving dendrite structures in 3D. This is a computationally demanding and time-consuming task, increasing with problem size. In this study, the lattice Boltzmann method (LBM) is chosen to describe the fluid dynamics as it can be massively parallelised using GPUs. The LBM is fully coupled to an external 2D and 3D solidification code, which uses the enthalpy method, to describe fluid flow during dendritic growth. The results of dendritic growth in external flow are in good agreement with the data found in the literature. The study shows that the LBM can be used to calculate flows fields much faster than conventional CFD approaches.