Grain Boundaries and Interfaces: Metastability, Disorder, and Non-Equilibrium Behavior: Grain Boundary Migration and Deformation: Part I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee, TMS: Chemistry and Physics of Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Yue Fan, University of Michigan; Liang Qi, University of Michigan; Jeremy Mason, University of California, Davis; Garritt Tucker, Colorado School of Mines; Pascal Bellon, University of Illinois at Urbana-Champaign; Mitra Taheri, Johns Hopkins University; Eric Homer, Brigham Young University; Xiaofeng Qian, Texas A&M University

Monday 8:30 AM
February 28, 2022
Room: 304C
Location: Anaheim Convention Center

Session Chair: Yue Fan, University of Michigan, Ann Arbor; Jeremy Mason, University of California, Davis; Garritt Tucker, Colorado School of Mines

8:30 AM Introductory Comments

8:35 AM  Invited
Grain Boundary Mobilities in Polycrystalline Materials: Jin Zhang1; Phillip Staublin1; Henning Poulsen2; James Warren3; Peter Voorhees1; 1Northwestern University; 2Technical University of Denmark; 3National Institute of Standards and Technology
    The mobilities of grain boundaries are fundamental to understanding grain growth processes in materials. By comparing the evolution of experimentally determined three-dimensional grain structures measured using diffraction contrast tomography to those derived from phase field simulation, we determine the reduced mobilities of thousands of grain boundaries. Through this approach the reduced grain boundary mobilities of over 1300 grain boundaries in iron are determined. We find that the grain boundary mobilities are largely independent of the five macroscopic degrees of freedom given by the misorientation of the grains and the inclination of the grain boundary. To further probe this large data set, a single order parameter, quantitatively accurate, phase field method that accounts for all five degrees of freedom of the grain boundary energy has been developed. The results of the phase field simulations and the potential role of trijunctions in the evolution of polycrystalline materials will be discussed.

9:05 AM  
Reconciling the Variability of Grain Boundary Migration Behaviors Using a Classical Approach: Eric Homer1; Darcey Britton1; Oliver Johnson1; Gregory Thompson2; 1Brigham Young University; 2University of Alabama
    Recent examinations of grain boundary mobility have demonstrated some very interesting phenomena, where, in addition to the expected thermally activated behavior, grain boundaries can exhibit non-Arrhenius temperature dependence as well as coarsening at cryogenic temperatures. We demonstrate that all these diverse behaviors are consistent with classical derivations of grain boundary migration and note the factors that control the change in observed migration behaviors. The case study to reinforce these observations is focused on the grain boundary migration of a single grain boundary type across a variety of metastable grain boundary structures. In addition to describing the classical model, we examine how the metastable structures might contribute to an expected migration behavior.

9:25 AM  
Emergent Disconnections in Phase Field Microstructure: Modeling Complex Boundary Migration at the Mesoscale: Mahi Gokuli1; Brandon Runnels2; 1California Institute of Technology; 2University of Colorado Colorado Springs
    Understanding, predicting, and controlling microstructure evolution is the one of the keys to designing next generation, high performance structural materials. Microstructure evolution is mediated by the motion of grain boundaries (GBs) in response to mechanical, thermal, or internal driving forces. The wide range of GB behavior makes them difficult to quantify and model predictively. Molecular dynamics, historically the workhorse of microstructure evolution, has limited application to large problems. Mesoscale modeling of microstructure evolution is attractive due to its scalability, but often oversimplifies the complex range of GB migration behaviors. Here, we use the multiphase field method, combined with the principle of minimum dissipation potential and strongly nonconvex GB energy, to simulate boundary migration. We show that disconnections, generally accepted as the mediators of boundary migration, appear spontaneously using this framework. The method is then applied to a number of cases of interest, including shear coupling, thermal softening, and geometric hardening.

9:45 AM  
Interactions between Interfacial Disconnections and Facet Junctions: Implications for Faceting and Boundary Evolution: Douglas Medlin1; Chris Barr1; James Nathaniel1; Elton Chen1; Ping Lu1; David Adams1; Rémi Dingreville1; Brad Boyce1; 1Sandia National Laboratories
    Interfacial line defects and their interactions are critical to understanding metastability and disorder in non-ground-state boundaries. Here, we consider the interplay between two types of interfacial line defect: disconnections and facet junctions. We begin by reviewing how such defects accommodate deviations in misorientation and inclination from ideal, low Σ configurations, illustrating this discussion with examples from atomic-resolution observations and simulations of boundaries vicinal to BCC Σ5 <001> and FCC Σ3 <111>. One question is how disconnections, which may be present to accommodate deviations in misorientation, interact with facet junctions. Our observations suggest that such disconnections can pin to the facet junctions and, in doing so, dictate the grain-boundary faceting length-scale. Implications for these interactions on dynamic behavior are discussed in the context of electron microscopic observations of grain boundary facet evolution under in-situ ion irradiation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

10:05 AM Break

10:20 AM  Invited
Does Grain Boundary Character Matter? Intergranular Failure in Al Alloys under Bending: Josh Kacher1; Sazol Das2; Yung Suk Jeremy Yoo3; 1Georgia Institute of Technology; 2Novelis Inc.; 3University of Michigan
    AA6xxx is a class of heat-treatable Al alloys that are attractive to the automotive industry due to their high strength-to-weight ratio. Past research has indicated that these alloys fail under bending via intergranular crack initiation and propagation, suggesting grain boundary engineering as a potential pathway towards increasing their fracture resistance. In this study, we employed multiscale electron microscopy techniques, including electron backscatter diffraction and site specific transmission electron microscopy, to investigate the role of microstructure in failure initiation under bending. We found that crack formation is actually offset slightly from the grain boundary plane. There was no correlation between grain boundary rotation angle and crack formation, though the angle between the sample surface and boundary plane did play an important role, with acute angles more likely to form cracks. Discussion will focus on the role of microstructure on dictating fracture initiation in AA6xxx.

10:50 AM  
Model for Grain Boundary Stress Field Evolution due to Dislocation-grain Boundary Interactions and Influence on Subsequent Slip Transmission: Darshan Bamney1; Laurent Capolungo2; Douglas Spearot1; 1University of Florida; 2Los Alamos National Laboratory
    Dislocation transmission across grain boundaries (GBs) often results in the formation of residual dislocations on the GB plane. In this work, a hybrid disclination-dislocation approach is introduced to model the regression of the GB stress state from equilibrium to nonequilibrium due to the incorporation of residual dislocations during coherent dislocation transmission. The model considers specifically time increments attributable to the dislocation source. The incorporation of residual dislocations causes altered screening characteristics in the NEGB stress field, which leads to locations of high resolved shear stress and low binding stress on the outgoing slip system. This model is implemented into a discrete dislocation dynamics code to simulate the influence of NEGB stress fields, conditioned by the slip transmission history, on subsequent dislocation transmission. DDD simulations reveal that the critical shear stress for dislocation transmission reduces with increased density of residual dislocation incorporation on the GB.

11:10 AM  
Effects of Segregated Solute Atoms and Clusters on Grain Boundary Properties in Magnesium Alloys: Vaidehi Menon1; Liang Qi1; 1University of Michigan
    It is known that the limitations in the room temperature formability and ductility of Mg alloys, which have great potential as lightweight structural materials, can be overcome by adding rare-earth and other alloying elements. Such improvements may result in variations of grain boundary (GB) properties. In this talk, we present a study of the segregation and co-segregation of solute elements (such as Y, Ca, Zn, etc.) along metastable GBs and special twin boundaries in Mg using density functional theory (DFT), molecular dynamics (MD), and hybrid Monte Carlo (MC)/MD methods. Based on optimized configurations of segregated solute atoms and clusters, phenomena like solute drag effects on GB migration and dislocation-GB interactions during deformation are investigated. These solute effects depend on the GB misorientation and other GB structural features, which further affect the texture formation during recrystallization and the overall mechanical behavior of Mg alloys.

11:30 AM  
Investigating Factors that Influence Stress-induced Grain Boundary Migration in Ultrafine-grained Metal Thin Films: Sandra Stangebye1; Yin Zhang1; Ting Zhu1; Olivier Pierron1; Josh Kacher1; 1Georgia Institute of Technology
    Grain boundaries play an increasingly important role in the deformation of ultrafine-grained (ufg) and nanocrystalline (nc) metals and are key to understanding and improving their mechanical properties. As grain size decreases, conventional dislocation glide is restricted and grain boundaries participate directly in deformation via grain boundary migration. In this talk, I will discuss results combining quantitative in situ transmission electron deformation experiments with orientation mapping in ufg Au thin films. This approach facilitates direct correlation of grain boundary migration behavior with a range of microstructure factors, including grain boundary misorientation/axis of rotation, CSL-number, grain size, Schmid/Taylor factor, etc. These factors were analyzed for hundreds of grain boundaries and correlated to the boundary migration behavior to establish which factors dictate grain boundary stability. Atomistic and finite element simulations were also conducted to provide an in-depth view on how the local stress state and grain boundary structure affects boundary migration behavior.

11:50 AM  
High-throughput Atomistic Simulations of Dislocation-grain Boundary Interactions: Sumit Suresh1; Michael Baskes1; Nithin Mathew1; Abigail Hunter1; Saryu Fensin1; 1Los Alamos National Laboratory
    Designing materials with specific mechanical properties requires an understanding of interaction between dislocations and microstructural features like grain boundaries (GB). Material models at larger length scales (microns or higher) are usually informed by classical molecular dynamics simulations that can explicitly model these interactions. In this work, high-throughput molecular dynamics (HTMD) simulations are performed for an extensive database (including symmetric and asymmetric tilt, twist boundaries) of well-characterized GB structures in copper, all interacting with a specific dislocation under different shear stresses. The MD simulations suggest that the local structure at the GBs, along with its misorientation angle, are crucial in determining the outcome of the dislocation-GB interaction. Higher scale crystal plasticity models can then be improved by incorporating the information from this HTMD dataset through a process of discretizing the output into strain-field descriptors (SFD), followed by training machine learning (ML) models.