Computational Thermodynamics and Kinetics: Defects and GBs I
Sponsored by: TMS Functional Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Chemistry and Physics of Materials Committee, TMS: Computational Materials Science and Engineering Committee, TMS: Integrated Computational Materials Engineering Committee, TMS: Solidification Committee
Program Organizers: Hesam Askari, University Of Rochester; Damien Tourret, IMDEA Materials Institute; Eva Zarkadoula, Oak Ridge National Laboratory; Enrique Martinez Saez, Clemson University; Frederic Soisson, Cea Saclay; Fadi Abdeljawad, Lehigh University; Ziyong Hou, Chongqing University
Monday 2:00 PM
March 20, 2023
Room: 26A
Location: SDCC
Session Chair: Danny Perez, Los Alamos National Laboratory; Timofey Frolov, Lawrence Livermore National Laboratory
2:00 PM Invited
Strong Entropic Contributions to Thermally-activated Kinetics: A Case-study in Dislocation Nucleation: Soumendu Bagchi1; Danny Perez1; 1Los Alamos National Laboratory
Harmonic transition state theory (HTST) has proved to be immensely successful at predicting the kinetics of a broad range of reactions in materials. It is however worth recalling that the accuracy of HTST relies on a set of assumptions whose validity should be assessed on a case-by-case basis. We discuss a situation, the emission of dislocation loops from surface steps, where HTST dramatically fails to reproduce the transition rates observed in direct MD. We show that a simple and efficient procedure to estimate the changes in vibrational entropy along the minimum energy pathway can resolve the discrepancy with HTST and provide quantitatively accurate predictions of the kinetics.
2:30 PM
Expanding Insights into Disconnections: Spencer Thomas1; Jason Trelewicz1; 1Stony Brook University
The Disconnection Model, which most notably explains shear-induced grain boundary migration, has ushered in a new understanding of grain boundary migration and sliding in general. However, we still only have a nascent understanding of disconnections themselves. This work reveals, via a combination of atomistic simulation and Kinetic Monte Carlo, many nuances of disconnection behavior – measuring disconnection energetics and mobility, size and doping effects, the effect of metastable grain boundary structures, and the behavior of disconnections on faceted asymmetric tilt grain boundaries. In particular, shear-coupled migration can be induced by differences in disconnection mobility rather than energetics; this can introduce sharp temperature dependence on grain boundary migration and sliding behavior.
2:50 PM
Universal Transition in Segregation Structures near Twin-boundary Disconnections: Chongze Hu1; Stéphane Berbenni2; Douglas Medlin1; Remi Dingreville1; 1Sandia National Laboratories; 2Université de Lorraine, CNRS, Arts et Métiers ParisTech
Twinning is a major deformation mechanism in nanocrystalline metals, and segregation of solute atoms at twin boundaries is a thermodynamic process that controls their stability and strengthening. In pristine, defect-free twin boundaries, solute segregation is generally uniform and symmetric across the boundary. However, when a disconnection, a type of interfacial line defect, is present, we report a universal segregation transition phenomenon for a broad range of binary alloys with different segregation structures. This transition in the segregation structure is explained by a break of the local symmetry across the disconnection terraces. Characteristics of the transition from one segregation structure to another are dictated by the orientation and character of the dislocation content of the disconnection, driven by changes in the local hydrostatic pressure field and local segregation volume in the vicinity of the boundary. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
3:10 PM
A Lattice Monte Carlo Approach to Spectral Grain Boundary Segregation: Thomas Matson1; Christopher Schuh1; 1Massachusetts Institute of Technology
Spectral information, which captures the full distribution of grain boundary environments, is necessary for a complete understanding of grain boundary solute segregation. Spectral grain boundary segregation models have recently been extended to include spectral solute-solute interactions, allowing for rigorous thermodynamics of polycrystals even at non-dilute concentrations. However, existing models are typically isotherms which rely on random mixing assumptions, and often fail when solute-solute interactions are strong relative to the available segregation energies. In this talk, we present a lattice Monte Carlo model that incorporates spectral grain boundary segregation, including solute-solute interactions, and takes direct atomistic measurements as input parameters. We use this model to analyze the interplay between solute-solute interactions and spectral segregation, and to illustrate the physical importance of the spectral approach. Lastly, we use thermodynamic integration to measure the configurational entropy and free energy as a function of grain size, which has relevance for nanocrystalline alloy design.
3:30 PM Break
3:50 PM
On the Variability of Grain Boundary Motion from a Diffusion Standpoint: Anqi Qiu1; Ian Chesser2; Elizabeth Holm1; 1Carnegie Mellon University; 2George Mason University
Molecular dynamics simulations are capable of tracking the motions of individual atoms in the materials system, and have revealed a lot about atomic diffusion mechanisms. It is usually expected that at a given temperature a bicrystal system with the same initial configuration should exhibit similar grain boundary motion rates. In an isolated cylindrical bicrystal system in which the inner cylindrical grain is left to shrink spontaneously, we observe a wide range of grain boundary mobilities with different initial velocity seeds. We also found that the mean squared displacements (MSD) of single atoms vary significantly with initial velocity seeds. In this work, we attempt to explain the mechanisms behind the dynamic heterogeneity of grain boundary motion, using atomic diffusion techniques developed for glass and super-cooled liquids, and to understand the correlations between atomic motion and grain boundary motion which is observed on the macroscopic scale.
4:10 PM
Propagation and Quantification of Microstructural Uncertainty in Molecular Dynamic Simulations of Polycrystalline Nickel: Meizhong Lyu1; Anqi Qiu1; Elizabeth Holm1; 1Carnegie Mellon University
Uncertainty quantification (UQ) and uncertainty propagation (UP) have received attention as they relate to the validity and robustness of simulation-based materials research; however, the sensitivity of the evolution trajectory to the initial conditions is not well-understood even in such familiar processes as polycrystalline grain growth. In an initial Molecular Dynamics (MD) study of four-grain junction decomposition (i.e. the T1 topological transformation), we found that the direction of decomposition depends on the random velocity seed. In other words, atomic-scale uncertainty resulted in macroscopically different outcomes. In this study, we demonstrate and quantify the uncertainty associated with the initial velocity of atoms in MD simulations of grain growth in polycrystalline nickel. We find that UP at the atomic scale can alter grains' growth or shrinkage trajectory at the microstructural scale; this has significant implications for comparing simulation results with experiments.
4:30 PM Invited
Modeling Grain Boundary Mediated Plasticity with Massively Parallel Atomistic Simulations: Timofey Frolov1; Nicolas Bertin1; Alexander Chernov1; Tomas Oppelstrup1; 1Lawrence Livermore National Laboratory
The plasticity of polycrystals is greatly influenced by grain boundaries (GBs), interfaces that can act as obstacles for dislocation motion. The resulting strengthening effect is described by the well-known Hall-Petch relation. A different strengthening mechanism referred to as dislocation starvation has also been demonstrated for small single crystals, where the bulk material is essentially dislocation-free and the plasticity is accommodated by dislocations nucleating at free surfaces. We perform large-scale MD simulations of bicrystal deformation to investigate the dynamic competition between dislocation multiplication in the bulk and their nucleation at GBs. We identify grain size and deformation rate regimes where the plasticity and strength are completely governed by the nucleation of dislocations at GBs. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.