Grain Boundaries and Interfaces: Metastability, Disorder, and Non-Equilibrium Behavior: On-Demand Oral Presentations
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 8:00 AM
March 14, 2022
Room: Mechanics & Structural Reliability
Location: On-Demand Room

Integrating Atomistic Modeling and In Situ Experiment to Decipher Grain Boundary Deformation Mechanisms: Ting Zhu1; Yin Zhang1; 1Georgia Institute of Technology
    With recent advances in atomistic modeling and in situ experimental technologies, there have been increased efforts to combine these approaches to understand the atomistic deformation mechanisms at grain boundaries (GBs). Here I will present our recent studies that integrate in situ electron microscopy, nanomechanical testing and atomistic modeling to investigate GB deformation mechanisms. For example, we have combined in situ high resolution transmission electron microscopy experiments and Monte Carlo simulations to unravel the atomic-scale processes of stress-driven GB sliding and structural transformation that occur unexpectedly at room temperature. We have also combined in situ MEMS-based nanomechanical testing and atomistic reaction pathway simulations to uncover the rate-controlling GB processes that dictate the experimentally measured activation volumes in nanocrystalline metals. The ability to resolve the atomic-scale dynamic processes of GB deformation, through coupled modeling and in situ experiment, enables a deep understanding of how GBs affect the plastic behavior of polycrystalline materials.

Immiscible Phase Interfaces: Controlling Irradiation Amorphization and Void Swelling: Janelle Wharry1; Priyam Patki2; Doruk Aksoy3; Timothy Rupert3; Wei-Ying Chen4; Shujuan Wang5; Yaqiao Wu5; Kristopher Darling6; 1Purdue University; 2University of Michigan; 3University of California - Irvine; 4Argonne National Laboratory; 5Boise State University & Center for Advanced Energy Studies; 6Army Research Laboratory
    The objective of this talk is to demonstrate how interfaces in nanostructured, immiscible binary alloys modulate structural and dimensional instabilities under irradiation. Nanostructuring is a longstanding alloy design strategy to increase resistance against irradiation-induced void swelling. But more recently, alloy design within a miscibility gap has shown exceptional potential for radiation tolerance. This study explores underlying mechanisms of the irradiation stability of nanostructured, immiscible Cu-10at.%Ta, with specific focus on Cu-Ta and Cu-Cu interfaces. We report on complementary transmission electron microscopy (TEM) in situ irradiations and molecular dynamics (MD) simulations. TEM in situ irradiation reveals a competition between amorphization and void nucleation at interphase boundaries, with amorphous Cu-Ta core-shell structures favored to form with lighter irradiating ions and at lower temperatures. MD confirms the point defect sink efficiency of an amorphous Cu-Ta interfacial phase. Results will be discussed in the context of engineering irradiation-stable nanostructured alloys.

Grain Boundaries Govern Plastic Deformation Kinetics in Nanocrystalline FCC Metals: Yin Zhang1; Kunqing Ding1; Sandra Stangebye1; Olivier Pierron1; Joshua Kacher1; Ting Zhu1; 1Georgia Institute of Technology
    Stress relaxation experiments and associated activation volume measurements represent one of the most effective ways of elucidating the strength/rate-controlling mechanisms governing the plastic deformation kinetics of polycrystalline metals and alloys. This approach has been well established in the study of conventional coarse-grained materials, and it has been recently extended to study ultra-fine grained and nanocrystalline metals. However, the currently available results of activation volumes for ultra-fine grained and nanocrystalline metals are limited and, more importantly, puzzling. Here, we conduct the atomistic calculations of activation volumes utilizing free-end nudged elastic band method. Combined with in situ TEM experiments and stress relaxation measurements in Au and Al, we determine the governing deformation mechanisms in nanocrystalline FCC metals.

Grain Boundary Wetting and Phase Transition in Al-Sn Alloy: Priya Tiwari1; Ranjit Dehury2; Abhay Singh Gautam2; 1Indian Institute of Technology, Bombay; 2Indian Institute of Technology, Gandhinagar
    Computational and experimental studies have increasingly provided details of the grain boundary (GB) wetting and phase transition in various alloys. In this work we present a detailed study of these transitions in polycrystalline Al-Sn eutectic system as a function of temperature, alloy composition and crystallography of GB. The transition temperature of these GB segregated phase was estimated using differential scanning calorimetry while the structural, compositional and morphological characteristics of the Sn rich GBs segregated phase as a function of alloy-composition and GB characteristics were studied using a combination of SEM, EBSD, EDS and XRD based techniques. Results obtained from these experiments will be combined to gain insight to wetting and phase transitions at the GBs.

Slip Transfer of Dislocations Across 3D Interfaces in a Cu/Nb System: Shuozhi Xu1; Justin Cheng2; Zezhou Li2; Nathan Mara2; Irene Beyerlein1; 1University of California-Santa Barbara; 2University of Minnesota, Twin Cities
    In metallic systems, 3D interfaces are heterophase interfaces that extend out of plane into the two crystals. Unlike 2D sharp interfaces across which the material properties change abruptly, the 3D interfaces provide a smoother intergranular transition in material properties. In addition, a 3D interface itself is chemically and crystallographically dissimilar from the two crystals that join. While many numerical studies of the interactions between dislocations and 2D interfaces have been conducted, fewer efforts were devoted to 3D interfaces in the same context. Here, we focus on the nanolayered Cu/Nb containing interfaces with 3D character. The slip transfer of dislocations across 3D interfaces are simulated via a phase-field dislocation dynamics (PFDD) method. In PFDD, the heterogeneities with a general geometry and plastic deformation on slip planes progress hand in hand. Selected simulation results are benchmarked against analytical solutions. Origins of the enhancement in strength and plasticity in the nanolaminates are discussed.

Deformation of Lamellar FCC-B2 Nanostructures Containing Kurdjumov-Sachs Interfaces: Relation between Interfacial Structure and Plasticity: Deep Choudhuri1; 1New Mexico Institute of Mining and Technology
    By coupling high-resolution transmission-electron-microscopy and molecular dynamics (MD) simulations we have investigated the deformation mechanisms prevalent in lamellar micro- structures containing soft fcc and hard bcc-ordered intermetallic B2, whose interfaces follow the Kurdjumov-Sachs (KS) orientation relationship. TEM/MD coupling indicated that the KS interface contained steps and ledges, with several steps exhibiting fcc-B2 lattice continuity between the {111}fcc and {011}B2. The KS-fcc (111) interfacial plane also contained periodically arranged 1/6<112>fcc partial dislocations with screw-like character, which were separated by extended dislocation “core-overlap” regions. We observed that the screw-like interfacial partials facilitated the KS interfacial sliding and strain accumulation at the interphase interfaces and reduced the yield strength of the composite material compared to a pure-fcc reference material. Deformation character also depended on B2 lamellae thickness: thinner B2 lamellae sheared via twinning to drastically lowered flow stress such that the flow-strength, while thicker B2 lamellae sheared via a slip-transfer mechanism.

Characterizing the Dynamics of Ion Hopping under the Effect of a Complex Stress Field Induced by the Micrometer-level Dislocation Pileup at a Non-equilibrium Grain Boundary: Liming Xiong1; 1Iowa State University
    Many plastically deformed polycrystalline materials contain a high density grain boundaries (GBs) far away from equilibrium. A blockage of dislocations by these GBs introduces high local stresses. The local stress/strain-assisted ion hopping along these GBs is not fully understood up to date because it remains a challenge using single-scale techniques to address the atomistic ion jumping, the GB structure together with the long-range stress evolution induced by the dislocation accumulation. To meet this challenge, here we present a concurrent atomistic-continuum (CAC) model to probe the coupling between the dislocation-mediated plastic flow and interstitial ion hopping along the non-equilibrium GBs. We have determined: (i) the correlation between the defect-induced stresses, the local structure distortion and the ion mobility; (ii) the decisive factor that dictates the diffusivities of non-equilibrium GBs with long-range heterogeneities.

Atom Probe Tomography Reveals Nickel’s Oxygen Solubility in Grains and Grain Boundaries after Oxidation: Jonathan Poplawsky1; Rishi Pillai1; QingQiang Ren1; Andrew Breen2; Baptiste Gault3; Michael Brady1; 1Oak Ridge National Laboratory; 2The University of Sydney; 3Max-Planck-Institut für Eisenforschung
    Oxidation resistance is important for material longevity within extreme environments. Accurate oxygen solubility measurements are necessary for computationally designing new high-strength, high-temperature oxidation resistant alloys. The oxygen solubility within pure metals, such as Ni, has been studied using a multitude of techniques, but atom probe tomography (APT) has not been used for this measurement. APT is advantageous because it offers a high chemical sensitivity (<10 ppm) and resolution (<1 nm) allowing for composition measurements within grain boundaries and nms of the oxide/metal interface. These regions were measured for a high and low purity Ni sample oxidized at 1000 °C for 48 hours by APT. The results show <10s of ppm oxygen solubility at all depths and 100s of ppm oxygen within GBs, suggesting that grain boundary diffusion is the most likely oxygen transport mechanism. APT was conducted at the CNMS, which is a U.S. DOE Office of Science user facility.

Faceting in Cylindrical Grain Boundaries: Anqi Qiu1; Ian Chesser2; Elizabeth Holm1; 1Carnegie Mellon University; 2George Mason University
    Isolated cylindrical grains shrink spontaneously under curvature driving force at high temperatures. With molecular dynamics simulations, we have observed that the grains remain mostly cylindrical throughout the shrinking process, but facets can appear. It is difficult to identify and characterize the facets that appear during the shrinking process with current simulation methods, as the facets appear and disappear very fast. When a synthetic driving force (SDF) opposing the curvature driving force is applied to drive the motion of the grain boundary in the other direction, the grain will expand and exhibit certain clear facets that do not easily disappear with the continuing motions of the grain boundary. For some cylindrical grain boundaries, the facets form octagonal shapes. This study on the expansion and faceting of cylindrical grain boundaries will give new insights on the properties of cylindrical grain boundaries.

A Framework for Continuum Modeling of Dislocation-grain Boundary Interactions in Polycrystalline Metals: Subhendu Chakraborty1; Abigail Hunter1; Darby Luscher1; 1Los Alamos National Laboratory
     Grain Boundary Engineering (GBE) is one the most important techniques to enhance the structural properties of polycrystalline materials. For better understanding of the mechanisms behind GBE, we need an appropriate continuum model to study the effect of grain boundary (GB) structure on the evolution of the dislocations within and across the grains. In this presentation we propose a continuum crystal plasticity model that incorporates the nucleation, annihilation and transmission of dislocations across the grain boundary. A novel modeling approach is introduced to represent the influence of GB characteristics (e.g. misorientation angle) on the resistance of the GB against dislocation transmission. Results will be provided to demonstrate the influence of GB structure on the evolution of plastic slip in a polycrystal microstructure.