Computational Thermodynamics and Kinetics: Solidification, Additive Manufacturing / Ordering, Coarsening and Patterning
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Nana Ofori-Opoku, Canadian Nuclear Laboratories; Eva Zarkadoula, Oak Ridge National Laboratory; Enrique Martinez Saez, Clemson University; Vahid Attari, Texas A&M University; Jorge Munoz, University of Texas at El Paso

Wednesday 8:30 AM
March 17, 2021
Room: RM 54
Location: TMS2021 Virtual

Session Chair: Nana Ofori-Opoku, Canadian Nuclear Laboratories; Vahid Attari, Texas A&M University; Eva Zarkadoula, Oak Ridge National Laboratory; Laurent Karim Béland, Queen's University


8:30 AM  Invited
Influence of Interphase Boundary Anisotropy on the Formation of Lamellar Eutectic Solidification Patterns: Mathis Plapp1; Supriyo Ghosh2; Sabine Bottin-Rousseau3; Silvère Akamatsu3; 1Ecole Polytechnique, CNRS; 2Los Alamos National Laboratory; 3Sorbonne Université, CNRS
    Lamellar eutectic two-phase growth is in principle well understood for alloys in which the solid-liquid and solid-solid interfaces are isotropic. However, there are numerous experimental observations that cannot be explained by theories and numerical models with isotropic interfaces, such as lamellar growth directions that markedly differ from the direction of the temperature gradient, or the emergence of large regions of perfectly aligned lamellae in large samples. We have developed a phase-field model in which the anisotropy of each interface can be controlled separately, and we have investigated the case of anisotropic solid-solid (interphase) boundaries. Results will be presented (i) on the selection of lamellar growth directions in thin-sample directional solidification, (ii) on the ordering of lamellae in bulk samples, and (iii) on the dynamics of spacing homogenization in inhomogeneous lamellar arrays. Simulation data will be compared to available theories and experimental data.

9:00 AM  
Thermokinetics and Associated Microstructural Evolution of Laser Powder Bed Fused Additively Manufactured Ti6Al4V: Mangesh Pantawane1; Narendra Dahotre1; 1University of North Texas
    The laser powder bed fusion additive manufacturing (LPBF-AM) often leads to thermokinetically evolved non-equilibrium microstructural state of the phases. The versatility of this additive manufacturing process can be exploited by understanding its thermokinetics by finite element method based three-dimensional computational modeling. In the laser powder bed fused Ti6Al4V, the non-equilibrium state of the martensitic phase can be realized by repetitive high cooling rates in the range of 4.82×105 K/s-2.56×105 K/s. Besides, the orientations of the prior β grains (002 texture), as well as the orientations of martensite laths within them, are influenced by the steep thermal gradients (1.48×106 K/m-5.18×107 K/m) directed at a given location and time. The martensitic laths further undergo the repetitive heating-cooling events while building a layer through multi-laser tracks and subsequent layers above it. This leads to compositional inhomogeneity within the martensite laths, as seen through atom probe tomography.

9:20 AM  Invited
Inhomogeneous Free Energies Beyond the Cahn-Hilliard Model: Interface Anisotropy and Equilibrium Patterning: Pascal Bellon1; Qun Li1; Robert Averback1; 1University of Illinois at Urbana-Champaign
    A real-space expansion of the free energy of inhomogeneous solid solutions is considered in binary alloys with pairwise interactions. In addition to the gradient-energy inhomogeneity term introduced by Cahn and Hilliard, this expansion yields a general expression for higher order terms. The coefficients of these higher-order inhomogeneities are fourth-rank, sixth-rank … (2n)th-rank tensors, which, for cubic lattices, introduce crystalline anisotropy and thus potentially modify the equilibrium shape of precipitates. Furthermore, each interaction shell introduces its own set of inhomogeneity coefficients, and the coexistence of multiple interactions can result in competing effects on phase stability. We illustrate these analytical results using phase field simulations to study in fcc alloys with interactions from first to fourth nearest neighbors (i) the equilibrium shape of precipitates and (ii) nanoscale compositional patterning in alloys with competing interactions. We also compare these results with Monte Carlo simulations and available experimental results.

9:50 AM  
Topological Transitions during Coarsening in Nanoporous Metals: Kate Elder1; W. Beck Andrews2; Markus Ziehmer3; Alexander Chadwick1; Erica Lilleodden3; Katsuyo Thornton2; Peter Voorhees1; 1Northwestern University; 2University of Michigan; 3Helmholtz-Zentrum Geesthacht
    Nanoporous metals are prototypical bicontinuous structures, consisting of pores and ligaments, that have a large surface area and coarsen by surface diffusion. Topological transitions, such as particle detachment, during coarsening have a large impact on mechanical properties of the microstructure and can lead to the formation of grain boundaries. Due to the length and time scales involved, most experimental nanoporous metal data is taken ex-situ, not allowing for constant observation of the microstructure during coarsening. An experimentally measured nanoporous gold structure is used as the initial condition for a phase field simulation of coarsening by surface diffusion. This modeling work confirms the presence of topological changes and curvature statistics provide insight into the morphology of the microstructure where a topological change would occur.