Computational Thermodynamics and Kinetics: Phase Transformation/Microstructure Modeling
Sponsored by: TMS Functional Materials Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Chemistry and Physics of Materials Committee
Program Organizers: Vahid Attari, Texas A&M University; Sara Kadkhodaei, University Of Illinois Chicago; Eva Zarkadoula, Oak Ridge National Laboratory; Damien Tourret, IMDEA Materials Institute; James Morris, Ames Laboratory

Wednesday 2:00 PM
March 2, 2022
Room: 255C
Location: Anaheim Convention Center

Session Chair: Kubra Karayagiz, Worcester Polytechnic Institute

2:00 PM  Invited
Morphological Evolution of Surface Instabilities during Vapor Co-deposition of Phase-separating Alloy Films: Rahul Raghavan1; Pei En Chen1; Yang Jiao1; Kumar Ankit1; 1Arizona State University
    The current understanding of how interfacial energies and surface contact angles influence nanostructural evolution and associated defects in vapor-deposited films is fairly limited. In view of this knowledge gap, we adopt a three-dimensional phase-field approach to numerically investigate the role of seed morphology and contact angles on the morphological evolution of surface protuberances in phase-separating alloy films. Film nanostructures are quantified using a statistical morphological descriptor, namely, n-point polytope functions, which provides a host of insights into the kinetic pathways while unraveling a hidden length scale correlation present at all contact angles. Using this technique, we decompose different symmetry features into canonical polytope symmetry groups to detect potentially distinct convergence and dynamics of evolution of different symmetry groups that comprise the film nanostructure.

2:30 PM  
High Performance Cahn-Hilliard Solver for Advanced Microstructure Modeling: Kubra Karayagiz1; David Montiel2; Siamak G. Faal1; Marcus Sarkis-Martins1; Adam Powell1; 1Worcester Polytechnic Institute; 2University of Michigan
    A robust solver scheme based on the convexity splitting technique is presented to obtain unconditionally stable time-stepping discretization when solving the Cahn-Hilliard equation with a logarithmic nonlinear free energy. In this approach, the free energy is split into concave and convex parts that are treated explicitly and implicitly, respectively. The numerical implementation is carried out using the finite element method in deal.ii, a C++ software library. The exact same problem is also solved using a fully explicit scheme, serving as a benchmark. The results from 2-dimensional and 3-dimensional simulations are presented. The methods are compared by means of computation time and accuracy. 50 to 200 speed-up is achieved using the explicit-implicit scheme as compared to the fully explicit scheme. A method for splitting free energy function terms in ternary and multicomponent systems is also discussed.

2:50 PM  Invited
Thermodynamic Investigation of Multicomponent Chloride Molten Salts for Spent Fuel Processing: Liangyan Hao1; Soumya Sridar1; Thomas Kirtley2; Ethan Schneider2; Elizabeth Sooby2; Wei Xiong1; 1University of Pittsburgh; 2University of Texas at San Antonio
    Pyroprocessing has been developed to recycle uranium from spent fuels and thus reduce radioactive wastes. To effectively monitor the change of thermodynamic properties and liquidus temperature for the molten salt electrolyte with composition, a multicomponent thermodynamic database for the KCl-LiCl-NaCl-UCl3-LnCl3 (Ln=La, Nd, Pr) will be established. Based on the SGTE Substance Database, fifteen binary systems and several key ternary systems have been optimized to satisfactorily reproduce experimental phase equilibria and thermodynamic properties data. Thermal analysis was firstly performed to study the phase equilibria in the KCl-NaCl-UCl3 and LiCl-NaCl-UCl3 systems and support the thermodynamic modeling. In this talk, we also highlight the importance of unifying the Gibbs free energy of the unary molten salts, which directly impacts the quality of the multicomponent database. The established molten salt database will contribute to the development of advanced reactors, such as small modular reactors.

3:20 PM  
Phase-field Model of Precipitation Processes with Spontaneous Coherency Loss: Tianle Cheng1; Youhai Wen2; 1U.S. Department of Energy, National Energy Technology Laboratory / NETL Site Support Contractor; 2U.S. Department of Energy, National Energy Technology Laboratory
    Coherency loss (CL) is a common process for precipitates during growth and Ostwald ripening. Existing models in the literature, however, treat all precipitates as either coherent or incoherent, without capturing the spontaneous process of CL or coupling CL with microstructure evolution. A phase-field model is proposed in which a special field variable is employed to describe the degree of coherency loss of each particle and its evolution is governed by a Ginzburg-Landau type kinetic equation. For the sake of computational efficiency, a flood-fill algorithm is introduced that allows the model to efficiently simulate coarsening of a large number of particles coupled with CL. The model is applied to simulate coarsening of Al3Sc precipitates in aluminum alloy and comprehensively compared with experiments. Simulation results clearly show how the particle size distribution is changed during CL and affects the coarsening rate.

3:40 PM Break

4:00 PM  
CALPHAD Modeling of Double Ordering: Yijia Gu1; Kyaw Hla Saing Chak1; Julia Medvedeva1; 1Missouri University of Science and Technology
    The nonstoichiometric κ carbide is a critical strengthening phase in lightweight high-strength steel FeMnAlC alloy. However, current CALPHAD sublattice models are not able to predict the correct C concentration in κ carbide phase due to the incomplete description of the octahedral interstitial sites (for C and vacancy). A 4-sublattice model is developed to describe the κ carbide in FeMnAlC alloy. The transformation from γ (fcc) phase to κ carbide can thus be considered as two consecutive ordering processes. The first one is the L12 ordering and the second is the ordering of C and vacancy. In this study, DFT calculations were performed for the formation energies of the 64 endmembers for the Fe-Mn-Al-Si-C system. The 4-sublattice model is explored to assess the phase stabilities with different temperature and C concentration.