Computational Thermodynamics and Kinetics: Phase Stability I
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
Tuesday 2:00 PM
March 16, 2021
Room: RM 54
Location: TMS2021 Virtual
Session Chair: Mira Todorova, Max Planck Institut fur Eisenforschung; Jorge Munoz, University of Texas El Paso; Hong Liu, KU Leuven; Eva Zarkadoula, Oak Ridge National Laboratory
2:00 PM Invited
Integrated Models for the Design of Precipitation Hardenable Mg and Al Alloys: Hong Liu1; Ioannis Papadimitriou2; Fengxiang Lin3; Javier Llorca4; Jian-Feng Nie5; Moelans Nele1; 1KU Leuven; 2IMDEA Materials ; 3UC Louvain ; 4IMDEA Materials; 5Monash University
This talk will present a simulation roadmap for virtual design of metallic alloys for engineering applications. The roadmap is based on a bottom-up, multiscale modelling approach. A key element of this approach is constructed using a phase field method that can quantitatively predict microstructure evolution at the meso-scale and can effectively connect basic physical and chemical properties computed by atomic-scale simulations and mechanical properties predicted by macro-scale simulations. This multiscale approach has been used to simulate and predict precipitate shape, plastic deformation and strengthening in light alloys. The computational results indicate that the shape of precipitates is determined by the competition of elastic strain and interfacial energies. They further indicate that a plate morphology of the precipitates is more effective than spherical shape in impeding dislocation gliding. These computational results provide a robust platform for rational design of engineering light alloys for better mechanical properties.
2:30 PM
Competing and Collaborating Phase Transitions Studied within Cluster Variation Method: Tetsuo Mohri1; 1Tohoku University
In an alloy system, it is often observed that multiple phase transitions take place in competing and/or collaborated manner. This includes a chemical ordering transition associated with magnetic ordering. Based on the spirit of Continuous Displacement Cluster Variation Method (CDCVM), we formulated multiple phase transitions within order-disorder transitions of a multicomponent alloy. In the CDCVM, displaced atoms from a Bravais lattice point are regarded as different atomic species and additional freedom due to the displacement is mapped onto configurational freedom of multicomponent alloy on a rigid lattice. In a similar manner, multiple phase transitions of a binary alloy originating from various internal freedoms are modelled by assigning different atomic interaction energies in a multicomponent alloy. The present study is able to deal with multiple phase transitions based on a single free energy formula.
2:50 PM
First principles Study of Precipitation in Al-Cu, Al-Li and Al-Cu-Li Alloys: Sha Liu1; Javier Llorca2; 1IMDEA Materials Institute; 2IMDEA Materials Institute & Technical University of Madrid
An analysis of precipitation in Al-Cu-Li alloys is carried out using first principles calculations. The formation enthalpies of the different phases at 0K determined with density functional theory and ground state phases and potential structures of Guinier Preston zones at low temperature are determined from the convex hull of the formation enthalpy. Then, the cluster expansion Hamiltonians are fitted from the formation enthalpy data using machine learning and the finite temperature thermodynamic properties of the different ground state phases are determined from low temperature expansions and Monte Carlo simulations with semi-grand canonical ensemble. In addition, the vibrational entropic contribution to the free energy of the phases is included using the harmonic approximation. This information is used to determine critical information (solvus temperatures, Gibbs free energy, etc.) of different metastable phases in the Al-rich part of the Al-Cu, Al-Li and Al-Cu-Li phase diagrams to optimize the heat treatments of these alloys.
3:10 PM Invited
Insights into Processes at Electrochemical Solid/Liquid Interfaces from Ab Initio Molecular Dynamics Simulations: Mira Todorova1; Sudarsan Surendralal1; Stefan Wippermann1; Florian Deissenbeck1; Christoph Freysoldt1; Joerg Neugebauer1; 1Max Planck Institut fur Eisenforschung
Processes at solid-liquid interfaces are at the heart of many present-day technological challenges related to the improvement of battery materials, electro-catalysis, fuel-cells, corrosion and others. Describing and quantifying the underlying fundamental mechanisms is equally challenging for experimental and theoretical techniques, and require methodological developments. Our recent developments of a novel potentiostat design [Surendralal et al., Phys. Rev. Lett. 120, 246801 (2018)] and a subsequent canonical thermopotentiostat [Deißenbeck et al. (submitted)] approach enable us to study solid/liquid interfaces under realistic conditions of applied bias. We utilize these developments to study the interaction of H with metal electrodes using ab-initio molecular dynamics. The study of the H/Pt/H2O system provides valuable insights into the role of the solvent on the workfunction evolution at metal/electrolyte interfaces. The applications of a bias to Mg/water interfaces allows us to elucidate the mechanism underlying the experimentally observed link between H-evolution under anodic conditions and Mg dissolution.
3:40 PM
Lattice Disorder and Amorphization in Oxygen-containing Immiscible Alloys: Qin Pang1; Bharat Gwalani1; Mathew Olszta1; Anqi Yu2; Krassimir Bozhilov2; Aashish Rohatgi1; Suveen Mathaudhu2; Arun Devaraj1; Peter Sushko1; 1Pacific Northwest National Laboratory; 2University of California Riverside
Room temperature solid-phase mechanical intermixing of immiscible metals can give rise to metastable structural motifs and properties that are impossible to realize by solidification of molten metals. Furthermore, these metastable structures can be affected by the presence of gaseous species, such as oxygen, that induce interfacial oxidation-reduction reactions and, thus, modify charge-density distribution.Here we use simulations based on the density functional theory (DFT) to examine thermodynamic stability of structural motifs contributing to the microstructural hierarchy of Cu-Nb alloys, observed experimentally, and investigate its dependence on the local Cu/Nb concentration ratio and on the concentration of oxygen impurities. We considered several types of structural models, including crystalline random alloys, phase segregated crystalline host-guest systems, and amorphous alloys and established the concentration window of bcc/fcc phase instability and conditions for amorphization accessible under shear deformation. Our ab initio molecular dynamics simulations suggest that charge disproportionation between Cu and Nb strongly favors the formation of NbOx resulting in Nb scavenging oxygen species and contributing to Nb/Cu segregation.
4:00 PM
A First-principles Analysis of the Temperature Dependence of Stacking Fault Energies in Mg and Ti: Julian Brodie1; Maryam Ghazisaeidi1; 1Ohio State University
Magnesium, titanium and their alloys are interesting for their high strength-to-weight ratio and application as structural metals in automotive and aerospace industries. However, these hexagonal-close-packed (hcp) metals suffer from an anisotropic plastic response resulting in insufficient slip systems available at low temperatures. As five independent slip systems are required for high ductility in polycrystalline metals, according to the von Mises criterion, activation of 〈c+a〉 dislocations are crucial in improving room temperature formability. We use density functional theory (DFT) and phonon analysis to determine the stability of dislocations in Mg and Ti at low temperatures. DFT is used to compute the stacking fault energy on relevant slip planes. Density Functional Perturbation Theory coupled with phonon analysis is used to determine how the free energy of stacking faults changes with temperature. Additionally, the BCC phases of Mg and Ti are studied for their potential role in the instability of certain 〈c+a〉 dislocations.
4:20 PM Invited
Vacancy-mediated Phase Selection in High-entropy Alloys: Prashant Singh1; Shalabh Gupta1; A V Smirnov1; Matthew J Kramer1; Duane D Johnson1; 1Ames Laboratory
We highlight the importance of vacancy-mediated stability in refractory high-entropy alloys (HEAs), where even small amounts of vacancies suppress chemical short-range order (SRO) and drive vacancy ordering. As an example, phase selection in Ti-Zr-Hf-Al alloys was investigated by in-situ high-energy X-ray diffraction, single-crystal X-ray diffraction, and density-functional-theory electronic-structure methods that address chemical disorder, including vacancies, predicting formation enthalpy, structure, density, and chemical SRO. Samples with varying Al content were synthesized, characterized, and computationally assessed to ascertain the composition-dependent phase selection, as increased Al content often acts as a stabilizer of a body-centered-cubic structure. Equiatomic TiZrHfAl was especially interesting due to its observed bcc superstructure, a variant of gamma-brass with 4 vacancies per cell. We highlight how vacancies mediate selection of this variant, driven by vacancy-atom SRO. As vacancies are inherent in processing refractory systems, similar discoveries may await in other high entropy alloys or in revisiting older experimental data.
4:50 PM
Lattice Dynamics of FeTi at Simultaneous High Temperature and High Pressure from First Principles: Adrian De la Rocha1; Jorge Munoz1; Armando Garcia1; Vanessa Meraz1; Bethuel Khamala1; Bert de Jong2; Yu-Hang Tang2; 1The University of Texas at El Paso; 2Lawrence Berkeley National Laboratory
FeTi is a brittle intermetallic compound that is stable in a large temperature and pressure range: up to 1600 K and at least up to 55 GPa, respectively. FeTi maintains the CsCl structure throughout and its Fermi surface is very simple, but it shows a remarkable variety of interesting physics, such as an anomalous phonon softening with temperature that has been attributed to a thermally-driven electronic topological transition, and phonon modes with negative Grüneisen parameters in a large volume range upon compression. We investigated the finite temperature lattice dynamics of FeTi at several volumes by fitting effective force constants to distributions obtained from a set of density functional theory calculations with atomic configurations selected by a learning algorithm using a graph-kernel-based similarity metric that minimize superfluous calculation. The force constants generally increase with pressure, but the Ti-Ti 2nd nearest-neighbors transverse bonds are anharmonic and change nonlinearly owing to charge redistributions.