4th International Congress on 3D Materials Science (3DMS) 2018: Dislocations, Twins, Strain, and Plastic Deformation III
Program Organizers: Hugh Simons, Denmark Technical University; Henning Poulsen, Denmark Technical University; David Rowenhorst, Naval Research Laboratory; Peter Voorhees, Northwestern University; Satoshi Hata, Kyushu Univ; McLean Echlin, UC Santa Barbara

Tuesday 3:50 PM
June 12, 2018
Room: Store Scene
Location: Kulturvćrftet (Culture Yard) Conference Center

Session Chair: Darren Pagan, Cornell University

3:50 PM  Invited
The Role of Atom Probe Tomography on the Development of the Next Generation of High Performance Materials: Paraskevas Kontis1; Surendra Makineni1; Leigh Stephenson1; Yanhong Chang1; Jonathan Cormier2; Dirk Ponge1; Dierk Raabe1; Baptiste Gault1; 1Max-Planck-Institut für Eisenforschung GmbH; 2Institut Pprime
    Understanding the deformation mechanisms observed in high performance materials allows to design strategies for the development of materials exhibiting enhanced performance. New insights into these mechanisms can now be gained through systematic, high-resolution characterisation, enabled by advanced characterisation methods that offer spatially resolved quantification of deformation, on the one hand, and composition on the other. We base our work on the combination of structural information gained from electron microscopy and compositional measurements from atom probe tomography (APT). Regarding the latter, recent instrumentation developments also allow us to investigate challenging mechanisms such as hydrogen embrittlement. The impact of APT on the interpretation of deformation mechanisms in superalloys and titanium alloys will be presented.

4:20 PM  
3D Reconstruction of The Spatial Distribution of Dislocation Loops with Least Square Fitting Approach: Hongbing YU1; Xiaoou Yi2; Felix Hofmann1; 1University of Oxford; 2University of Science and Technology Beijing
    We propose a new approach for reconstructing the 3D spatial distribution of small dislocation loops (DLs). It is based on fitting of specific DLs in multiple weak-beam dark field TEM micrographs recorded at different tilt angles. Each DL is identified in all the projections where it appears using a forward prediction approach. A system of linear equations can then be setup, linking the 3D position of each DL to its 2D position in each projection. If more than 2 projections are available, this system of equations is over-determined and the 3D position of each DL is found by least square fitting. This approach is applied to the damage formed by low-dose self-ion implantation in tungsten. The results are in good agreement with the damage microstructure recovered using a generalized weighted back-projection method. The advantages of the new triangulation approach are discussed in detail.

4:40 PM  
An Elastic-visco-plastic Deformation Model and In Situ Micro-testing Of Al-Li: Alexander Staroselsky1; Luke Borkowski1; John Sharon1; 1Utrc
     Recent developments have produced a third generation of Al-Li alloys that provide not only weight savings, but also good fatigue performance, strength and toughness combination and compatibility with standard manufacturing techniques. Analyses of 3D microstructure and its correlation with properties need to be performed to determine optimal material processing. We develop physics based models for prediction of microstructure evolution and material properties of Al-Li alloy 2070. An elastic-plastic crystal plasticity model is developed and incorporated in finite element software. The model accounts for microstructural evolution during non-isothermal non-homogeneous deformation and is coupled with the damage kinetics. It bridges the gap between dislocation dynamics and continuum mechanics scales. Model parameters have been calibrated against lab tests including micro-pillar in-situ simple compression and simple shear tests. We present detail description of these nano-scale characterization in-situ testing. Numerical predictions are verified against the lab results including stress-strain curves and crystallographic texture evolution

5:00 PM  
On the Dislocation Content of Random Grain Boundaries in Full 3D: Diana Farkas1; Bryan Kuhr1; 1Virginia Tech
    The dislocation content within the structure of random fully 3D grain boundaries in an FCC polycrystal was investigated through Molecular Dynamics modeling and the Dislocation Extraction Algorithm (DXA) for detecting lattice dislocations. It was found that a large fraction of the boundaries studied contained significant numbers of lattice dislocations as part of their structure, mostly Shockley partial dislocations and perfect lattice dislocations. The observed dislocation content varied widely depending on specific boundary geometrical parameters and relaxation state. Virtual tensile straining of these samples revealed how the dislocation content changed as a function of the strain applied to the sample. The results are discussed in the context of the role of the multiplicity of possible grain boundary structures on the deformation response of polycrystalline materials.

5:20 PM  
3D Characterization of Dislocations in an Al-Cu-Mg Alloy: Zongqiang Feng1; Chengwei Lin1; Guilin Wu1; Xiaoxu Huang1; 1Chongqing University
    Quantitative characterization of morphological and crystallographic features of dislocations and dislocation structures in crystalline materials is of great importance to fully understand many dislocation-related phenomena and processes. The advent and development of dislocation tomography provides new capability for three dimensional characterization of morphological features of dislocations. However, the coupling of morphological features with the crystallographic characteristics of dislocations is still lacking. In this study, we combined electron dislocation tomography and correlative crystallography analysis to achieve high throughput characterization of geometrical and crystallographic parameters of dislocations in a water-quenched Al-Cu-Mg alloy. The obtained results led to new insight into the formation mechanisms of different dislocation features in the quenched alloy.

5:40 PM  
Characterization of 3D Dislocation Structure in Single Grains and Parent-twin Pairs of Uniaxially Deformed Polycrystalline Mg AZ31 Alloy Specimens: Gyula Zilahi1; Gábor Ribárik1; Sean Agnew2; Wei Wu3; Ulrich Lienert4; Tamás Ungár1; 1Eötvös University; 2University of Virginia; 3The University of Tennessee; 4Deutsches Elektronen-Synchrotron
    Magnesium alloys became popular lightweight structural materials during the last two decades. However, poor formability at room temperature is a key issue. Easy slip systems with the shortest, ⟨<b>a</b>⟩ type Burgers vectors cannot accommodate compression or tension along the <b>c</b> axis. {101̅2}⟨101̅1̅⟩ type twinning is an important mechanism of <b>c</b> axis tension, however it can accommodate limited amount of strain and it allows for unidirectional shear only. Earlier TEM studies also confirmed the activation of ⟨<b>c</b>+<b>a</b>⟩ type dislocations. High angular resolution 3D individual crystal diffraction measurements were carried out at the 1-ID beamline of APS synchrotron at Argonne National Laboratory. 788 grains of three plastically deformed samples were analyzed. Possible parent-twin relationships were identified based on the 3 dimensional misorientations. Dislocation structures of individual grains are characterized in terms of Burgers vectors and edge or screw character dislocations. The results are discussed in terms of earlier experimental and modeling studies.

6:00 PM  
Site-specific Property Maps of Additively Manufactured SS316L Using a Mesoscale, Multi-physics Modeling Framework: Nadia Kouraytem1; Carl Herriott1; Xuxiao Li1; Wenda Tan1; Vahid Tari2; Anthony Rollett2; Ashley Spear1; 1University of Utah; 2Carnegie Mellon University
    The microstructure of additively manufactured (AM) metals has been shown to be quite heterogeneous and exotic compared to conventionally manufactured metals. Consequently, the effective mechanical properties of AM-metal parts are expected to vary both within and among different builds. This talk presents a multi-physics modeling framework for simulating process, microstructure, and properties of AM-metal volumes. The framework predicts 3D-microstructural nucleation for a multi-pass, multi-layer Selective Laser Melting (SLM) process. The solidified microstructure is automatically sub-sampled to perform virtual mechanical testing using crystal-plasticity FFT modeling. The effective stress-strain response of each sub-sampled volume is then automatically analyzed to extract effective mechanical properties, which are used to generate property maps showing the spatial variability of mechanical properties throughout the simulated-build volume. As a demonstration, the framework is applied to SLM SS316L volumes processed with different laser parameters. The multi-physics framework and property maps could provide a path toward qualification of AM-metal parts.