Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales: Session VI
Program Organizers: M Arul Kumar, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Levente Balogh, Queen's University; Josh Kacher, Georgia Institute of Technology; Caizhi Zhou, Missouri University of Science and Technology; Lei Cao, University of Nevada, Reno

Thursday 8:00 AM
October 3, 2019
Room: G132
Location: Oregon Convention Center

Session Chair: Jette Oddershede, Xnovo Technology ApS; Jean-Charles Stinville, University of California, Santa Barbara

8:00 AM  Invited
Measurements of Plastic Localization in Polycrystalline Materials in Relation to 3D Microstructure: Jean-Charles Stinville1; P. G. Callahan1; M. A. Charpagne1; M. P. Echlin1; E.R. Yao1; J. Shin1; F. Wang1; P. Villechaise2; J. Cormier2; D. Texier3; V. Valle2; D.S. Gianola1; T. M. Pollock1; 1University of California, Santa Barbara; 2Institut P' - UPR 3346, CNRS - Université de Poitiers - ENSMA; 3Institut Clément Ader - UMR CNRS 5312
    To develop predictive models for monotonic and cyclic loading of polycrystalline metallic alloys, there is a need for quantitative assessment of plastic localization at the nano- and micro- scales. The development of two sets of advanced experiments for measurements of plastic localization will be discussed. First, the combination of SEM and DIC has emerged as a robust method for quantification of the strain fields at the plastic localization scale. The use of the Heaviside-DIC method provides a unique opportunity to capture quantitatively the plastic localization on large representative fields of view. The second set of experiments employ in-situ Transmission Scanning Electron Microscopy measurements on targeted microstructural configurations to elucidate the effect of microstructure on the dislocation dynamics that accompany strain localization. The combination of these two sets of experiments coupled with the characterization of the 3D microstructure of metallic alloys provides critical information for predictive models of cyclic loading.

8:30 AM  Invited
Towards Rapid Throughout Measurement of Grain Boundary Properties: Jin Zhang1; David Rowenhorst2; Akinori Yamanaka3; Henning Poulsen4; Peter Voorhees1; 1Northwestern University; 2Naval Research Laboratory; 3Tokyo University of Agriculture and Technology; 4Technical University of Denmark
    A method is developed to measure grain boundary properties by comparing the evolution of experimentally determined 3D grain structures to those derived from phase field simulations. Grain evolution in pure iron is determined in three dimensions and as a function of time using synchrotron-based diffraction contrast tomography. The temporal evolution of over 1300 grains is quantified. This provides information on the morphology and kinetics of over 8000 grain boundaries in a single experiment. Using a time step from these data as an initial condition in a phase-field simulation, the computed structure is compared to that measured experimentally at a later time. An optimization technique is then used to find the reduced grain boundary mobility that yields the best match to the simulated microstructure. The ability to measure the dependence of grain boundary mobilities and energies on the five macroscopic degrees of freedom will be discussed.

9:00 AM  
Orientation Specific Deformation Behavior of Twins in Mg Alloy AZ31: Chaitanya Paramatmuni1; Fionn Dunne1; 1Imperial College London
    We present here an integrated experimental and numerical investigation of the effect of twin orientation on its deformation behaviour. The high resolution electron back scatter diffraction (HR-EBSD) measurements of the deformed microstructure show that geometrically necessary dislocation (GND) density and twin-resolved shear stress (TRSS) inside twins increase with the angle between twin c-axis and loading direction (henceforth called inclination angle). In order to understand further, a finite element based strain-gradient crystal plasticity formulation is employed to simulate the sequential twin shear transformation. It is observed that the twin shear transformation influenced by twin orientation affect the local mechanical fields inside the twin and at its vicinity, with negligible contribution from the parent and neighbouring grains. Similar to the experimental observations, the numerical results show that the TRSS increases with the inclination angle from a negative to a positive value, which questions the current perception of twin shear transformation induced back-stress.

9:20 AM  
A New Method for Calculating Stress Fields Generated from Heterogeneous Plastic Deformation Using High-Energy X-ray Diffraction and Field Dislocation Mechanics: Darren Pagan1; Armand Beaudoin2; 1Cornell High Energy Synchrotron Source; 2University of Illinois at Urbana-Champaign
    A general consensus exists that localization of plastic deformation at the crystal scale leads to damage initiation. Procedures for determining stresses generated by heterogeneous plastic deformation have existed for over 50 years, but their use has been limited by an inability to quantify full 3-D plastic deformation fields experimentally. In this presentation, we demonstrate how lattice orientation data measured using high-energy X-ray diffraction and crystal plasticity kinematics can be used to reconstruct slip activity and plastic deformation fields. Subsequently, this data is inserted into a finite element, field dislocation mechanics formulation to calculate stresses generated by plastic deformation heterogeneities. The new methodology is used to analyze the stresses within and stability of shear bands that appear during uniaxial compression of a copper single crystal. We find that shear bands that appear are in a low energy configuration and stabilized by small amounts of secondary slip at the band edges.

9:40 AM  
Measurement of the Thermal Expansion of Ti-7Al using High Energy X-Ray Diffraction Microscopy: Rachel Lim1; Darren Pagan2; Joel Bernier3; JY Peter Ko2; Anthony Rollett1; 1Carnegie Mellon University; 2Cornell High Energy Synchrotron Source; 3Lawrence Livermore National Laboratory
    Hexagonal metals have anisotropic coefficients of thermal expansion, and there is little agreement in literature on the CTEs for these metals. High energy x-ray diffraction microscopy, a non-destructive, in situ, microstructural characterization technique, has been used to determine the anisotropic coefficients of thermal expansion (CTEs) for Ti-7Al. Polycrystalline α-phase Ti-7Al was continuously heated from room temperature to 850°C while far-field HEDM scans were being taken. The lattice parameters at a given temperature were calculated based on the median of lattice parameters of the individual grains. The results showed the CTEs were different in the a- and c-directions, and both dropped as a function of temperature. The equivalent strain and von Mises stress were found to be lower after the thermal cycle with the outliers in the initial state having shifted the most. The CTEs were refined by modeling a synthetic microstructure using a thermo-elastic fast Fourier transformation-based micromechanical model.

10:00 AM Break

10:20 AM  Invited
Mapping Grain Morphology and Orientation by Laboratory Diffraction Contrast Tomography: Jette Oddershede1; Jun Sun1; Florian Bachmann1; Hrishikesh Bale2; William Harris2; Erik Lauridsen1; 1Xnovo Technology; 2Carl Zeiss X-ray Microscopy Inc.
    Recent developments of the Laboratory Diffraction Contrast Tomography (LabDCT) technique have extended its capabilities to include full reconstruction of the 3D grain structure, including both grain morphology and crystallographic orientation. LabDCT makes use of high resolution diffraction images acquired on a ZEISS Xradia 520 Versa X-ray microscope. The 3D crystallographic imaging capabilities of LabDCT complements the structural data obtained by traditional absorption-based tomography and together they provide unprecedented insight into materials structure. We will present a selection of LabDCT results with particularly emphasis on its non-destructive operation. We will discuss boundary conditions of the current implementation, compare with conventional synchrotron approaches, point to the future of the technique and discuss ways in which this can be correlatively coupled to both related characterisation techniques and microstructural modelling for better understanding of materials structure evolution in 3D.

10:50 AM  Invited
Mapping of Geometrically Necessary Dislocation Densities using Electron Backscattering Diffraction: Travis Skippon1; 1Canadian Nuclear Laboratories
    Transmission electron microscopy (TEM) allows for the observation of individual dislocations, but sample size constraints make any bulk measurements impractical. Conversely, X-ray diffraction allows for the measurement of volume averaged dislocation density of bulk samples, but the spatial resolution is limited to the size of the diffraction volume (often many thousands of grains for engineering materials). Electron Backscattering Diffraction (EBSD) is a technique that is ideal for filling the gap between these two techniques. Through careful analysis of local distortions in crystal orientation, dislocation density measurements are possible with sub-micron spatial resolution over length scales as high as millimetres. This approach allows for the relative proportions of various dislocation types to also be determined, which is particularly useful for HCP materials where both <a> and <c+a> type dislocations must be accounted for. All of this information is extracted from typical EBSD measurement techniques without the need for specialized equipment.

11:20 AM  
Backtracking 5DOF Grain Boundary Hydrogen Diffusivities in High-Purity Nickel: Experimentation, Localization Techniques, and Inverse Problem Theory: Sterling Baird; Christian Kurniawan1; Tyler Critchfield1; David Page1; Katie Varela1; David Fullwood1; Eric Homer1; Oliver Johnson1; 1Brigham Young University
    Localization techniques can be used to infer a 5 degree-of-freedom structure-property model for the diffusivity of hydrogen through grain boundaries from indirect measurements on polycrystals. Heterogeneous data from both experimental measurements (EBSD, X-ray diffraction, hydrogen permeation measurements) and simulations that span multiple length scales (atomistic and mesoscale) can be synergistically combined to obtain a structure-property model. Microstructural processing, characterization, and diffusivity measurements are discussed. Localization techniques applied to grain boundary networks significantly reduce experimental complexity and cost associated with mapping the 5-dimensional grain boundary property design space, leading to a high-fidelity, low-cost, kinetic structure-property model for materials engineering applications.

11:40 AM  
Imaging Microplasticity Events by Combining High Energy Diffraction Microscopy and Bragg Coherent Diffraction Imaging: Matthew Wilkin1; Anthony Rollett1; 1Carnegie Mellon University
    Understanding plasticity events at the grain scale is key to the development of mesoscale models. High Energy Diffraction Microscopy (HEDM) has proven effective for determining grain-averaged elastic strain and grain orientation in a sample, but it provides no local strain information. Bragg Coherent Diffraction Imaging (BCDI) has been shown to provide 3D strain fields in individual grains but has largely been applied only to nano-particles, rather than polycrystals. We propose combining these two methods to image the interaction between several grains in a polycrystalline sample. HEDM gives us a 3D map of a microstructure in a sample, providing orientations for each grain. These orientations can be used to locate Bragg peaks for neighboring grains, allowing us to employ BCDI to investigate in 3D the interaction between two neighboring grains during heating or loading and the migration of defects within a particular grain.