Seeing is Believing -- Understanding Environmental Degradation and Mechanical Response Using Advanced Characterization Techniques: An SMD Symposium in Honor of Ian M. Robertson: Advanced Characterization II: Multi-modal Analysis Techniques
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 2:30 PM
March 1, 2022
Room: 207C
Location: Anaheim Convention Center
Session Chair: Kaila Bertsch, Lawrence Livermore National Laboratory; Kelly Nygren, Cornell University/CHESS; Stephen House, University of Pittsburgh/ECC; Khalid Hattar, Sandia National Laboratory; Josh Kacher, Georgia Institute of Technology
2:30 PM Invited
Connecting Plasticity to Hydrogen Embrittlement Using High Energy Synchrotron X-rays: Timothy Long1; Kelly Nygren2; Matthew Miller1; 1Cornell University; 2Cornell High Energy Synchrotron Source
Professor Robertson’s group has a long successful history of characterizing differences between hydrogen charged and uncharged specimens on the subgrain scale using TEM. Recently, his group has used high pressure torsion (HPT) of Nickel samples to produce samples with a range of large plastic strains without the complications of a fracture surface. This work used these HPT samples to understand plasticity differences by studying the distributions of intragrain lattice orientations using high energy x-ray diffraction (HEXD) at the Cornell High Energy Synchrotron Source (CHESS). Compared to uncharged specimens, some hydrogen-charged crystals had orientation distributions with larger skewness and kurtosis values. Using a simple kinematic model for plastic slip, strain heterogeneity was show to be a possible explanation of the differences. To study the evolution of the orientation distributions, in situ HEXD experiments to smaller plastic strains were also conducted on nickel samples. Consistent results were obtained.
3:00 PM Invited
Graph-based Analysis of Deforming Polycrystals: Darren Pagan1; Austin Benson2; Matthew Kasemer3; 1Pennsylvania State University; 2Cornell University; 3University of Alabama
A polycrystal can naturally be thought of as a network of connected grains through which load and deformation is transferred. With the recognition of this network structure, it is apparent that polycrystals can be represented more formally by graphs. In addition, the huge range of tools that have been previously developed to analyze and predict the behavior of various structures represented by graphs, including social networks and traffic patterns, can be taken advantage of. Here we describe the application of graphs to analyze and understand large three-dimensional descriptions of polycrystal microstructure and micromechanical response, including those measured using high-energy diffraction microscopy and generated synthetically. A focus will be the use of graph-based machine learning (graph neural networks) for the prediction of mechanical response of polycrystals.
3:30 PM Invited
Slip Transfer at Grain Boundaries Investigated with 2-D and 3-D Experimental Measurements: Thomas Bieler1; Harsha Phukan1; Chelsea Edge1; Zhuowen Zhao1; Ruxin Xu2; Martin Crimp1; Philip Eisenlohr1; Carl Boehlert1; 1Michigan State University; 2Argonne National Laboratory
Identification of slip processes at grain boundaries is complex and challenging for characterization and modeling. To enable modeling of heterogeneous deformation near grain boundaries, credible observations with good statistics are necessary, as the size of grain boundary misorientation space combined with slip system activation is huge. Recent work with 2-D characterization of slip transfer (direct or indirect transmission of dislocations through grain boundaries), has provided statistics, but TEM provides details at the atomistic scale that cannot be obtained otherwise. However, the extraction of a TEM foil removes the state of stress that drives the slip transfer process. To overcome this limitation, differential aperture x-ray microscopy enables micron-scale quantification of geometrically necessary dislocations (GNDs) present near grain boundaries with the concurrent local elastic stress state in an in-situ loaded sample. Insights gained from this analysis of GNDs and discernment of slip transfer will be discussed.
4:00 PM Break
4:15 PM Invited
Incorporating Dislocations into the Simulation of EBSD Patterns: Marc De Graef1; 1Carnegie Mellon University
Electron Back-Scatter Diffraction (EBSD) has for nearly three decades been used primarily to acquire orientation information in polycrystalline/polyphase materials, during the last decade also in 3D serial sectioning experiments. The closely related Electron Channeling Contrast Imaging (ECCI) technique can image near-surface defects, but it is unclear if EBSD patterns can be used similarly. The high resolution cross-correlation approach can determine strain fields with high accuracy, so there is defect information in an EBSD pattern. We present a novel approach to the simulation of EBSD patterns for crystalline materials that contain near-surface defects. The approach is beased on physics-based forward models for pattern formation but incorporates the defect displacement field as well as the electron beam interaction volume. We will present examples of single dislocation "imaging" as well as the effect of multiple dislocations on pattern sharpness. Preliminary results for displacement fields from discrete dislocation dynamics will be shown.
4:45 PM Invited
Visualization and Analysis in Additive Manufacturing: Anthony Rollett1; 1Carnegie Mellon University
Additive manufacturing is multiscale. In laser powder bed fusion (LPBF), millions of microscopic weld tracks build parts over hours. High-speed visualization of the melting process with synchrotron x-rays is a prime example of “seeing is believing” because it has revealed near omnipresence of vapor holes and the many different ways that defects can be introduced into printed parts. The details of the melt pools also need metallography and orientation mapping to reveal subtle variations of melt pool shape. Simulation of microstructure development imparts an understanding of the evolution and its sensitivity to processing details. High speed diffraction experiments, again with synchrotron x-rays, reveals unexpected aspects of phase evolution that are complemented by microscopy to reveal microsegregation despite the high cooling rates. Deeper analysis reveals multiple precipitation sequences in alloy 718, surprising variations in lattice parameters in Ti-6Al-4V, and competition between ferrite and austenite in stainless steels.