Seeing is Believing -- Understanding Environmental Degradation and Mechanical Response Using Advanced Characterization Techniques: An SMD Symposium in Honor of Ian M. Robertson: Deformation and Plasticity
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Chemistry and Physics of Materials Committee, TMS: Corrosion and Environmental Effects Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Kaila Bertsch, Lawrence Livermore National Laboratory; Khalid Hattar, University of Tennessee Knoxville; Josh Kacher, Georgia Institute of Technology; Bai Cui, University of Nebraska Lincoln; Benjamin Eftink, Los Alamos National Laboratory; Stephen House, University of Pittsburgh; May Martin, National Institute Of Standards And Technology; Kelly Nygren, Cornell University; Blythe Clark, Sandia National Laboratories; Shuai Wang, Southern University of Science and Technology
Tuesday 8:00 AM
March 1, 2022
Room: 207C
Location: Anaheim Convention Center
Session Chair: Josh Kacher, Georgia Institute of Technology; Stephen House, University of Pittsburgh/ECC; Blythe Clark, Sandia National Laboratory
8:00 AM Invited
Elucidating Dislocation-interface Interactions via In Situ Straining in the Electron Microscope: Nathan Mara1; 1University of Minnesota
In this presentation, we report on the plastic deformation mechanisms in lamellar nanocomposites as a function of decreasing layer thickness. Utilizing Physical Vapor Deposition (PVD), Accumulative Roll-Bonding (ARB), and cast lamellar eutectics, nanolamellar composites with layer thicknesses to just a few nanometers may be investigated. Using these three techniques, the textures, interfacial defect structures, and deformation mechanisms can be systematically investigated. For instance, deformation twinning is observed in the Cu copper phase in Cu-Nb ARB material as opposed to PVD material. Evolution of preferred interfacial structures during processing will be linked to the structure, energetics, and kinetics of a given interface type, and validated via in-situ straining experiments in the TEM. Mechanical properties and behavior will be discussed in terms of the effects of interfacial content on deformation processes at diminishing length scales, and defect/interface interactions at the atomic scale.
8:30 AM Invited
Interaction of Glide Dislocations with Interfaces in Mg Alloys: M. T. Andani1; Z. Huang1; C. Yang1; A. Lakshmanan1; L. Qi1; V. Sundararaghavan1; J. Allison1; Amit Misra1; 1University of Michigan
An overview of the interaction of basal <a> dislocations with interfaces in Mg alloys will be presented. In the case of dilute, aged Mg-Nd alloys, in situ indentation in TEM shows that matrix dislocations pile-up at beta-1 precipitate interfaces in the confined regions. Dislocation theory and density functional theory calculations indicate that planar precipitate “walls” result in a strong but not impenetrable barrier to slip transmission. In dilute Mg-Al single phase alloys, high-resolution electron backscatter diffraction is used to measure barrier strength of specific GBs to specific slip systems. The results are analyzed using dislocation pile-up model and used to calibrate grain size strengthening parameters in a crystal plasticity model. Integration of local experimental measurements of dislocation-interface interactions with computational modeling at corresponding length scales is shown to be effective in developing predictive models of alloy strength.
9:00 AM Invited
Investigation of Slip Transmission through a Complete Grain-level Assessment of the Stress-strain Evolution in Polycrystalline Alloys: Michael Sangid1; John Rotella1; Diwakar Naragani1; Jun-Sang Park2; Peter Kenesei2; Paul Shade3; 1Purdue University; 2Argonne National Laboratory; 3Air Force Research Laboratory
While many seminal studies of slip transmission in polycrystalline materials have been conducted in the past decades, typically the resolved stress state is approximated based on the nominal stress on the specimen. In this work, multi-modal experimental techniques are presented to measure and track the complete micromechanical state, evolving during loading, of each and every grain within the regions of interest. Specifically, a combination of high-energy X-ray diffraction microscopy and digital image correlation coupled with electron backscatter diffraction are conducted on a specimen for each of the alloys, (fcc) Haynes 282 and (hcp) Ti7Al. Higher resolution imaging is used for identification of the slip system activity and subsequently used to study slip transmission events in the Ti7Al specimen. An accurate knowledge of the resolved shear stress in adjacent grains (grain interactions) is demonstrated to be a key descriptor of the slip transmission events.
9:30 AM Break
9:45 AM Invited
Deformation by Dislocations, Twinning, and Phase Transformations in Compositionally Complex FCC Solid Solutions: Michael Mills1; Connor Slone2; Jiashi Miao1; Veronika Mazanova1; Mulaine Shih1; Milan Heczko1; Maryam Ghazisaeidi1; 1Ohio State University; 2Exponent
The equiatomic CrCoNi alloy is an fcc solid solution that exhibits intriguing behaviors including very large strain hardening and cyclic hardening rates, large fracture toughness, and strong dependence of the yield strength at low temperature. Detailed characterization using a variety of electron microscopy methods has revealed that these behaviors are closely linked to the interplay between dislocation-mediated plasticity, microtwinning, and an fcc-to-hcp transformation. The development of these mechanisms as a function of deformation for both ambient and cryogenic temperatures is discussed. The effect of Al and Ti, and the formation L12 short-range ordering domains, on the deformation mechanisms will also be presented. Fundamental insights into these experimental results are also provided by density functional theory, atomistic, and continuum-level calculations.
10:15 AM Invited
Multifaceted Research in Plasticity: Huseyin Sehitoglu1; Sameer Mohammed1; 1University of Illinois
Significant progress has been made made in the 1950s through the early 1990s establishing important phenomenological laws in microstructure-property relations. With the advent of major innovations of experimental and theoretical tools from 1990s to 2020s, the last two decades in particular has witnessed considerable advances in the knowledge of microplasticity that shape our modern understanding of microstructural influences on deformation response. For the current generation of scientists and researchers, advancement of novel alloys essentially requires delving deeper into an atomic level understandingof the structure-property relationship devoid of empiricism. The new materials include nanograined alloys, shape memory materials and steels that undergo twinning deformations. We present an overview of advances in prediction of flow stress under slip and twinning and supporting TEM investigations with applications to fatigue behavior and transformation behavior in different classes of materials.
10:45 AM Invited
Modeling Grain Boundary Mediated Plasticity with Massively Parallel Atomistic Simulations: Timofey Frolov1; Nicolas Bertin1; 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 and DD 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 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.