Grain Boundaries and Interfaces: Metastability, Disorder, and Non-Equilibrium Behavior: Poster Session
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 5:30 PM
February 28, 2022
Room: Exhibit Hall C
Location: Anaheim Convention Center

G-27: Fractal-like Grain Exfoliation in Liquid-metal-activated Aluminum-water Reactions: Peter Godart1; Douglas Hart1; 1Massachusetts Intitute of Technology
    Understanding aluminum-water reactions is critical for applications ranging from corrosion prevention to hydrogen generation. It has been shown that such reactions can be accelerated by the introduction of liquid metal phase into the grain boundary network of the aluminum. Little was known about the exact mechanism by which this process occurs, though, in part due to challenges with using analysis techniques like SEM and XRD in a highly dynamic aqueous environment. In this work, a method is presented for reacting aluminum treated with a eutectic gallium indium alloy with water arbitrarily slowly via controlled exposure to room-temperature water vapor, enabling in-progress analysis via SEM and XRD techniques. Using this approach, a two-part reaction mechanism was observed for the first time in which the aluminum first disintegrates along its micro- and nano-scale grain boundaries via a fractal-like exfoliation process, followed by the reaction between unpassivated aluminum grains and ambient water molecules.

G-28: Investigation of the Effect of Heating Rate on the Recrystallization of Deformed Samples of Polycrystalline High-purity Niobium: Zackery Thune1; Nathan Fleming1; Conor McKinney1; Elizabeth Nicometo1; Thomas Bieler1; 1Michigan State University
    The consistent production of high-purity niobium superconducting radiofrequency cavities is crucial for enabling improvements in accelerator performance. Currently, assembled cavities are vacuum heat-treated to 800C for approximately three hours. Recent studies have shown that dislocations and grain boundaries trap magnetic flux which dissipates energy and degrades performance. Based on this understanding, the heat-treatment should reduce the number of dislocations and sub-grain boundaries. We hypothesize that the current heating rate is too slow and therefore facilitates recovery, rather than recrystallization, which does not reduce the number of geometrically necessary dislocations (GNDs) that are strongly correlated to trapped magnetic flux. For this study, vacuum heat-treatments at different heating rates were conducted and electron backscatter diffraction (EBSD) was used to investigate the effect of heating rate on the extent of recrystallization in samples of polycrystalline high-purity niobium from rolled sheets and formed cavities.

G-29: Numerical Determination of the GND Footprint of Dislocation Loops: Connecting Atomistic Descriptions with Experimental Observations: Sicong He1; Jaime Marian1; 1University of California, Los Angeles
    We present a numerical methodology to generate computational Nye-tensor signals for comparison with experimental data in irradiated fine-grained materials. Our approach links atomistic simulations of self-interstitial atom clusters gliding towards low-angle grain boundaries in body-centered cubic iron with experimental renditions of Nye-tensor norm maps to facilitate the interpretation of damage microstructures. The linking component consists of a three-dimensional model that calculates the Nye tensor norm of arbitrary dislocation arrangements and assigns a corresponding signal intensity to each segment to emulate experimental contrast intensities. We demonstrate the potential of the model in interpreting atomistic and experimental data by studying the Nye-tensor signature change for the dislocation loop as its getting absorbed by the grain boundary. We find that the Nye tensor norm behaves qualitatively differently at various stages.

G-30: The Dimensionality of Absorbed Defects Dictates GB Response to Irradiation: Chang-Yu Hung1; James Nathaniel1; Emily Hopkins1; Khalid Hattar2; Mitra Taheri1; 1Johns Hopkins University; 2Sandia National Laboratories
    Grain boundary (GB) has been considered an effective defect sink for radiation-induced defects, including point defect, cluster, and dislocation loop. The progression of GB absorption from point defect absorption and recombination to loop absorption may lead to different GB responses. This study performed an in-situ irradiation technique to examine GB-mediated mechanisms of defect absorption in response to continuous irradiation in a model pure Au. At first, fluctuations of defect density occurring at the GB is a self-healing process, likely aided by GB microstate change. However, at high dpa, a defect denuded zone is closed, followed by denuded zone re-opening. The denuded zone re-opening at higher dpa is associated with a pronounced strain field induced by extensive loop interaction with GB that causes loop absorption and rapid GB structure changes.

G-31: The Effect of Grain Boundaries on High-temperature Microstructure Evolution in Cu/Nb Composites: Emmeline Sheu1; Jon Baldwin2; Michael Demkowicz1; 1Texas A&M University; 2Los Alamos National Laboratory
    We investigate the mechanisms of high temperature microstructure evolution in Cu/Nb composites using a combination of experiments and simulations. To that end, we synthesize specialized, model samples consisting of a Cu layer embedded between two thicker Nb layers. The Cu layer terminates along a straight edge within the composite. Contrary to initial expectations, this edge does not coarsen or retract upon high temperature annealing. Phase field modeling shows that the stability of the terminating edge of the Cu layer is due to anchoring by grain boundaries in the neighboring Nb layers. This work advances understanding of microstructure evolution in two-phase metal composites, enabling improved predictions of their performance at elevated temperatures.