Grain Boundaries and Interfaces: Metastability, Disorder, and Non-Equilibrium Behavior: Grain Boundary Migration and Deformation: Part II
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

Tuesday 2:30 PM
March 1, 2022
Room: 304C
Location: Anaheim Convention Center

Session Chair: Yue Fan, University of Michigan, Ann Arbor; Jeremy Mason, UC-Davis

2:30 PM  
Slip Transfer and Cracking at Grain Boundaries in FCC and HCP Metals: Eugenia Nieto-Valeiras1; Maral Sarebanzadeh2; Meijuan Zhang3; Alberto Orozco-Caballero2; Javier Llorca1; 1IMDEA Materials Institute & Technical University of Madrid; 2Technical University of Madrid; 3IMDEA Materials Institute
     Grain boundaries (GBs) are considered as obstacles to dislocation motion which lead to marked increased in strength in polycrystals. Nevertheless, there is ample experimental evidence that slip transfer across GBs is possible depending on the geometrical criteria, leading to different types of GBs. Tensile tests were carried out in thin foils of polycrystalline fcc (Al, Ni) and hcp (Mg, Ti) metals. The orientation of the grains in the surface was determined by means of electron back-scattered diffraction and dislocation activity in each grain on the foil surface was assessed by means of slip trace analysis. The geometrical criteria that lead to either opaque or transparent GBs were assessed for each material from this information. In addition, stress concentrations at the opaque GBs were analyzed as potential sources of GB cracking. The results of the mechanical tests were complemented with crystal plasticity simulations that included GB cracking using cohesive surfaces.

2:50 PM  Invited
Mechanisms for and Thermodynamics of Interfacial Strain Mediation: Shen Dillon1; 1University of California, Irvine
    Interfacial line defects can serve as point defect sources and sinks. Those that exhibit climb oin the process can mediate strain during process such as Coble creep and densification. These defects are inherently non-equilibrium, and little experimental or computational work has detailed their structure, thermodynamics, or kinetics. This talk will describe efforts to experimentally characterize the energy barriers and activation volumes associated with nucleating strain mediating interfacial line defects using high temperature in situ Coble creep and sintering experiments.

3:20 PM  
Grain Boundary Pop-in during Nanoindentation of W: Recent Observation on Dislocation Grain Boundary Interaction: Karsten Durst1; 1TU Darmstadt
    Nanoindentations were performed in the vicinity of grain boundaries (GBs) in polycrystalline tungsten, observing in some cases a secondary grain boundary pop-in in the load–displacement curve. The dislocation microstructure in the plastic zone of the residual impression was analysed using sequential polishing, electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) analysis on and below the surface. A significant hardness increase was observed before the GB pop-in event. The careful ECCI analysis on polished cross sections shows the dislocation pile-up in the vicinity of the GB along with transmitted dislocations in the adjacent grain. For some indentations, the interaction of the dislocations within the plastic zone and the GB leads to a localized GB movement on or below the surface. The occurrence and magnitude of GB movement are found to be strongly influenced by misorientation between the adjacent grains, the orientation and distance of the indenter to the GB.

3:40 PM  
A Crystal Plasticity Framework to Model Continuum Disconnections in Polycrystals: Junan He1; Himanshu Joshi1; Nikhil Chandra Admal1; 1University of Illinois at Urbana-Champaign
    In this talk, we present a geometrically non-linear continuum model to describe shear coupling/GB plasticity within the disconnections-framework of GB motion, with an eventual goal to simulate large polycrystals. GBs are described as diffuse interfaces whose motion results in a plastic distortion (Fp) of the material. Fp describes plastic slip due to the combined effect of disconnections corresponding to various discrete modes. By accounting for the contribution of Fp in the multiplicative decomposition of the deformation gradient (F = FeFp), we demonstrate that an effective coupling predicted by the model not only depends on the available disconnection modes but also on the nature of the driving force, as observed in molecular dynamics simulations. In addition, we highlight the key differences between our crystal plasticity-based model and recent models for continuum disconnections.