Advanced Characterization Techniques for Quantifying and Modeling Deformation: Local Strain / Misorientation I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Shaping and Forming Committee, TMS: Materials Characterization Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; Thomas Bieler, Michigan State University; Marko Knezevic, University of New Hampshire; Irene Beyerlein, University of California, Santa Barbara; Wolfgang Pantleon, Technical University of Denmark; C. Tasan, Massachusetts Institute of Technology; Arul Kumar Mariyappan, Los Alamos National Laboratory

Tuesday 2:00 PM
February 25, 2020
Room: Theater A-2
Location: San Diego Convention Ctr

Session Chair: Wolfgang Pantleon, Technical University of Denmark; Todd Hufnagel, Johns Hopkins University


2:00 PM  Invited
Quantitative X-ray Phase Contrast Imaging of Granular Media under Dynamic Impact: Todd Hufnagel1; A.F.T. Leong1; Vignesh Kannan1; Kaliat Ramesh1; 1Johns Hopkins University
    The response of granular-materials to dynamic loading is complicated due to their heterogeneous structure. Imaging the material provide detailed information about the evolution of structure. But under dynamic-loading there is not enough time to record the multiple projections required for tomography, and we are restricted to collecting single, 2D-projections of complex 3D structures. In this talk, we describe x-ray phase-contrast imaging (XPCI) studies of the structure of geological materials subjected to dynamic-deformation. Although the XPCI images are too complex for direct interpretation, using a robust algorithm we can extract quantitative structural information, including the porosity and mean pore size. We illustrate the application of this algorithm to dynamic wedge impact of sandstone. Formation of an extended wedge of compacted material in front of the indenter induces dilation further downfield, leading to intergranular cracking and fracture. This study provides new insights into the connections between mesoscale mechanisms and macroscopic mechanical behavior.

2:30 PM  
The Critical Microstructural Conditions for Void Nucleation During Ductile Rupture: Dislocation Structures and Vacancy Condensation: Philip Noell1; Julian Sabisch1; Douglas Medlin1; Brad Boyce1; 1Sandia National Laboratories
    Ductile rupture usually involves structural degradation from the nucleation and growth of voids and their coalescence into cracks. To understand the role of dislocations during void nucleation, the present study presents ex-situ cross-sectional observations of interrupted deformation experiments revealing incipient, subsurface voids in a copper material containing copper oxide inclusions. The local microstructural state was evaluated using electron backscatter diffraction, transmission electron microscopy, and transmission kikuchi diffraction. Surprisingly, before substantial growth and coalescence has occurred, the deformation process resulted in the nucleation of hundreds of nanoscale voids per cubic micrometer in the deeply deformed neck region. Analysis of multiple microscale voids suggests that dislocation boundaries facilitate the growth process. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

2:50 PM  
3D Maps of Geometrically Necessary Dislocation Densities in FCC Polycrystalline IN718: Wyatt Witzen1; Andrew Polonsky1; Tresa Pollock1; Irene Beyerlein1; 1University of California Santa Barbara
    Three dimensional Electron Backscatter Diffraction (3D EBSD) as a method of orientation analysis offers the ability to characterize material microstructure in 3D space, allowing the calculation of Geometrically Necessary Dislocation (GND) densities. Feature reference misorientation within each grain imaged in this dataset reveals that some grains exceed 20 degrees in misorientation to the overall orientation of the grain, leading to the partitioning of subgrains and other areas of high misorientation within single grains. This orientation imaging technique allows GND density mapping in 3D space and provides insight to these subgrain features, particularly useful for additively manufactured material characterization. In this study, GND densities ranging from roughly 1 × 1011 to 1.8 × 1013 m-2 have been calculated from the high degree of misorientation within these grains. Additionally, GNDs are calculated using different nearest-neighbor environments to understand how disorientation measured over different neighborhood configurations will influence the GND densities calculated.

3:10 PM  
Cyclic Deformation in Tension and Compression of Pure Aluminium Monitored In-situ by High-resolution Reciprocal Space Mapping: Annika Diederichs1; Ulrich Lienert2; Wolfgang Pantleon1; 1Department of Mechanical Engineering, Technical University of Denmark; 2DESY Photon Science, Deutsches Elektronen Synchrotron
    Commercially pure aluminium is cyclically deformed in symmetric tension and compression while monitoring the microstructure by high-resolution reciprocal space mapping. The synchrotron technique enables resolving subgrains, orientation spread and elastic stresses in individual grains. Following four grains through 10000 tension compression cycles, reciprocal space maps were gathered after different number of cycles and through five subsequent cycles. More pronounced changes occur within individual load cycles than during an increase in number of cycles. Radial profiles revealed a characteristic behavior: the integral width follows a butterfly pattern and the asymmetry changes sign corresponding to the applied stress, but increases markedly during unloading. Based on the observation of a larger asymmetry in the unloaded state than at maximum tension or compression and the behavior of individual subgrains tracked during the cycles, necessary modification of the composite model for cyclic deformation (even in its refined version) are outlined.

3:30 PM Break

3:50 PM  
In situ Synchrotron and EBSD Study of H-induced Local Stresses: Jinwoo Kim1; Haoxue Yan1; S. Mohadeseh Taheri-Mousavi1; C. Cem Tasan1; 1Massachusetts Institute of Technology
    Hydrogen embrittlement of structural metallic materials is a long-pending problem for various industries, and the interaction between hydrogen and crystallographic defects plays the key role in this phenomenon. Our recent investigations have revealed that hydrogen segregation at grain boundaries lead to increased local stresses, which can induce micron-scale dislocation activity in the vicinity of grain boundaries that are at the surface of sheet metal. In this present work, we investigate the effect of the H-induced stress fields in the bulk. To this end, we designed a novel in situ H charging setup for synchrotron X-ray diffraction, which enables a real-time diffraction analysis in transmission mode during H-ingress. The diffraction results in combination with cross-correlation EBSD analyses and simulations suggest how the H-induced stress fields can cause local crystallographic changes in adjacent grains in steels, even in absence of any externally applied stress.

4:10 PM  Cancelled
Connecting the Evolution of Grain-scale Stresses and Intragranular Lattice Orientations to Slip System Activity in a Deforming Ti-7Al Alloy Using High Energy X-ray Diffraction: Kelly Nygren1; Jean-Charles Stinville2; Marie-Agathe Charpagne2; Tresa Pollock2; Matthew Miller3; 1Cornell High Energy Synchrotron Source; 2University of California, Santa Barbara; 3Cornell University
    Far-field High Energy X-Ray Diffraction Microscopy (ff-HEDM) boasts the powerful and unique ability to capture the evolution of the grain-scale microstructure and stress during a continuous in-situ mechanical test. A recent advancement in the data reduction algorithm for ff-HEDM enables the extraction of both grain-scale stress tensors and the intragranular orientations for each grain in a 1 mm3 volume of a polycrystal (~1000 grains) during the continuous loading of an alloy. The list of orientations present in each grain at each time step is called the Grain Orientation Envelope (GOE). To elucidate the fundamental relationship between slip and the evolving microstructure in a Ti-7Al alloy, the relationships of slip system activity (including kinetics) to the GOE and stress tensor within each grain are probed. The data are interpreted and cross-correlated with Heaviside Digital Image Correlation (H-DIC) measurements of surface grains in the same sample taken before and after loading.

4:30 PM  
Hierarchical Microstructure in Shear Bands of Pure Titanium: Xiaolong Ma1; Dexin Zhao1; Dinakar Sagapuram1; Kelvin Xie1; 1Texas A&M University
    A comprehensive understanding of shear band microstructure is the key to control the ductility of materials. However, large localized deformation usually develops within this thin region and nanoscale recrystallized grains are formed. Conventional characterization techniques such as EBSD and regular TEM imaging are inadequate to visualize the detailed microstructure inside these shear bands. For example, EBSD cannot provide high enough spatial resolution. TEM has the ability to determine the nanoscale grain size, but to elaborate the orientations of all grains is labor-intensive. Moreover, detailed orientation information cannot be obtained. In this work, we demonstrated that ASTAR (a technique that acquires the diffraction pattern of each pixel) could offer direct orientation information of microstructure feature down to 1 nm scale. Using the ASTAR results, we revealed the hierarchical structure including high-angle grain boundaries, low-angle grain boundaries, defect bundles in the shear bands.

4:50 PM  
Characterizing Residual Stress Gradients Due to Shot Peening: Comparison Between X-ray and Nanoindentation Techniques: Siavash Ghanbari1; David Bahr1; 1Purdue University
    Residual stresses generated during surface enhancement processing form gradients that can be probed via a variety of techniques. We develop a model-based analysis of the impact of residual stresses in metals on nanoindentation load-depth curves. A shot peened high strength steel was used as an experimental validation benchmark, with surface residual stresses characterized with a “cosine alpha” method x-ray detection system and compared directly to those determined via nanoindentation. The lateral sensitivity of the indentation method was demonstrated to be on the order of 10 micrometers, with a lower limit determined by a combination of the surface roughness and ensuring the tip is fully within the self-similar geometry. The indentation method shows more point to point variation than the 2 mm spot size x-ray technique, but the average does converge to the x-ray method value.

5:10 PM  
A Continuum Mechanics Description of EBSD Misorientation Mapping: Shao-Shi Rui1; Shaolou Wei1; Hui-Ji Shi2; Cemal Tasan1; 1Massachusetts Institute of Technology; 2Tsinghua University
    Electron backscatter diffraction (EBSD) based kernel averaged misorientation (KAM) and grain reference orientation deviation (GROD) maps are frequently used in the characterization of plastic deformation distribution and failure modules for metallic alloys under various service conditions. In this presentation, we will discuss their physical origin by combining theoretical considerations with integrated in-situ SEM/EBSD experiments. The main goal is to address the following questions: (i) What are the definitions of KAM and GROD from continuum mechanics perspective? (ii) What are the dislocation types and local deformation states that KAM and GROD quantitatively describe? (iii) How applicable are KAM and GROD in assessing the plastic deformation of single- and poly-crystalline metals? In addition, we will also discuss the feasibility of breaking down the KAM value into several sub-parameters to achieve more insights regarding local deformation states.