Advanced Characterization Techniques for Quantifying and Modeling Deformation Mechanisms: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Shaping and Forming Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; John Carpenter, Los Alamos National Laboratory; Thomas Beiler, Michigan State University; Khalid Hattar, Sandia National Laboratory; Wolfgang Pantleon, DTU; Irene Beyerlein, Los Alamos National Laboratory

Tuesday 6:00 PM
February 28, 2017
Room: Hall B1
Location: San Diego Convention Ctr

L-1: Analysis of Compact Forced Simple-Shear and Compact Forced Double-Shear Specimens for Shear Localization in Materials: Thomas Lebrun1; 1Los Alamos National Laboratory
    Adiabatic shear band formation is an observed failure indicator in metals during high strain-rate events. The compact forced-simple-shear specimen (CFSS) and the newly-designed compact forced-double-shear specimen (CFDS) have been developed to produce pure mode-II in-plane (simple) shear in order to observe this phenomenon. These samples can be readily loaded into high strain-rate testing equipment such as the Split-Hopkinson Bar, while providing the means to align their 2-D planes of shear along specified directional features of a material’s microstructure. The stress state evolution in the shear zone can be extracted from experimentation to develop constitutive strength, damage evolution, and failure models. This study compares the shear strength and deformation path symmetry of the CFSS and CFDS in HF-1 and Ductile Case Steel over a range of strain rates and orientations. Mechanical testing has shown expected similarities between shear strength and EBSD analysis of the deformation paths is underway.

L-2: Characterization of a Biocompatible Co-Cr-W Alloy by means of Correlative Microscopy and Nanoindentation Experiments: Irmgard Weissensteiner1; Patrick Voigt2; Helmut Clemens1; Verena Maier-Kiener1; 1Montanuniversität Leoben; 2Titanium Solutions GmbH
    In dental technology implants are often produced by a CAD/CAM process from cast Co-Cr alloys. The high content of additional alloying elements leads to the formation of intermetallic phases which deteriorate the machinability. To optimize the microstructure a detailed material characterization is required. In this work, the characterization of a Co-24Cr-8W-3Mo (m.%) alloy was performed by SEM in order to evaluate the phase fractions and EDX as well as atom probe tomography to analyze the distribution of the alloying elements in the constituent phases. EBSD was used to determine the crystal structure of the intermetallic phases. The influence of hot isostatic pressing on phase chemistry, phase fractions and hence the mechanical properties was studied by nanoindentation experiments. A slight strain rate sensitivity, a crystal orientation anisotropy as well as a different susceptibility to strain-induced martensitic transformation was observed, which is finally correlated to the different microstructures and matrix compositions.

L-3: Displacement Rate and Temperature Equivalence in Stochastic Cluster Dynamics Simulations of Irradiated Pure alpha-Fe: Aaron Dunn1; Brittany Muntifering2; Remi Dingreville2; Khalid Hattar2; Laurent Capolungo3; 1TMS; 2Sandia National Laboratories; 3Los Alamos National Laboratory
    Charged particle irradiation is a frequently used experimental tool to study damage accumulation in metals expected during neutron irradiation. Understanding the correspondence between displacement rate and temperature is one of several factors that must be taken into account in order to design experiments that produce equivalent damage accumulation to neutron damage conditions. In this study, spatially resolved stochastic cluster dynamics (SRSCD) is used to simulate damage evolution in alpha-Fe and find displacement rate/temperature pairs under `target' and `proxy' conditions for which the local distribution of vacancies and vacancy clusters is the same as a function of displacement damage. Results are presented for Frenkel pair irradiation and displacement cascade damage in thin films and bulk alpha-Fe. The methodology presented in this study allows for a first-order prediction of the temperature at which ion irradiation experiments (`proxy' conditions) should take place in order to approximate neutron irradiation (`target' conditions).

L-4: Error Analysis of the Dictionary Approach to Electron Backscatter Diffraction Indexing: Farangis Ram1; Saransh Singh1; Marc De Graef1; 1Carnegie Mellon University
    The dictionary approach is an alternative to the standard 2D Hough transform approach to electron backscatter diffraction (EBSD) indexing, and is particularly effective for low crystal symmetry or very low quality EBSD patterns. The pattern orientation is determined by comparison with a dictionary of dynamical, forward modeled EBSPs. We report on the efficacy of the dictionary approach. Efficacy is quantified through evaluation of the error of estimated orientations and disorientations. Error analysis is performed using test patterns simulated by a dynamical EBSD forward model. Simulated patterns that closely resemble experimental patterns are key to this analysis. Error analysis reveals that for a cubic material, in a standard EBSD set-up with an almost 80 capture angle and a 1% of pattern width error in projection center, the mean orientation accuracy is 1° with a standard deviation of 0.2°. To achieve this accuracy, a collected pattern size of 30×30 pixels is sufficient.

L-5: Microstructural Development During Particle/Substrate Impacts in Cold Spray of Gas Atomized Aluminum Alloy Powders: Benjamin Bedard1; Tyler Flanagan1; Sumit Suresh1; Avinash Dongare1; Seok-Woo Lee1; Harold Brody1; Xuemei Wang2; Victor Champagne3; Mark Aindow1; 1University of Connecticut; 2United Technologies Research Center; 3U.S. Army Research Laboratory
    A summary will be presented of our characterization studies on single-pass cold spray trials of gas-atomized Al 6061 powder onto substrates of the same alloy in a standard microstructural condition. A combination of SEM, FIB sectioning, and TEM studies has been used to investigate the microstructural features in the feedstock powder particles and in individual powder splats. These data are used to reveal the nature of the microstructural development in the earliest stages of cold spray deposition. It is shown that the silicide and iron-bearing phases adopt a characteristic distribution in the powder, and that these act as internal markers to reveal the localization of shear within the splats. The absence of these phases in the redeposited jetted material, and the adoption of characteristic columnar grain structures in such regions, is used to show that localized melting is occurring at the interface under the deposition conditions used in this study.

L-6: NiAl Oxidation Reaction Processes Studied In Situ Using MEMS-Based Closed-Cell Gas Reaction Transmission Electron Microscopy: Kinga Unocic1; Dongwon Shin1; Raymond Unocic1; Lawrence Allard1; 1ORNL
    The nanoscale oxidation mechanisms and kinetics was investigated using in situ closed-cell gas reaction scanning transmission electron microscopy (STEM) in a model β-NiAl system. Here, we directly visualize the dynamic structural and chemical changes that occur during high temperature oxidation at high spatial resolution of 50.3Ni-49.7Al (at. %) nanoparticles under static air conditions at ~1 atm (760 Torr) with heating up to 750°C at 5 °C/s. A MEMS based gas cell system, with microfabricated heater devices and a gas delivery systems was used to reveal site-specific oxidation initiation sites. The results from these in situ oxidation experiments in the β-NiAl system will be discussed.

L-8: The Thermal Stability of Cr-Cu Nanostructured Materials Revealed at the Atomic Resolution: Zaoli Zhang1; Jinming Guo1; Julian Rosalie1; 1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences
    The thermal stability of nanostructured Cr-Cu materials prepared by extreme deformation was explored at the atomic resolution using modern spherical aberration-corrected transmission electron microscopy (TEM) via simultaneous in-situ imaging and spectroscopy analysis. The evolution of the structural and chemical composition in the nanostructured materials with temperature was tracked in real-time. It demonstrates that the nanostructured materials are not only subjected to a structural change but also to an obvious chemical composition fluctuation upon annealing. The destabilization process in the nanostructured materials starts at a quite early stage. Real-time analysis reveals the chemical composition changes with temperature, and allows further deriving the diffusion coefficients, and analyzing the dynamic behavior in nanocrystalline materials in details.

L-9: Unidirectional Fibre Composite Characterisation from X-ray Tomography: Monica Emerson1; Ying Wang2; Kristine Jespersen1; Lars Mikkelsen1; Philip Withers2; Knut Conradsen1; Vedrana Dahl1; Anders Dahl1; 1Technical University of Denmark; 2The University of Manchester
    Unidirectional fibre composites are widely used material systems and are employed for the load carrying parts of wind turbine blades. To reduce the cost of energy, blades are becoming longer, which requires the materials to be able to support more stress. Image analysis and statistics can be used to predict mechanical properties and damage mechanisms while loading. These estimates can be compared to models and measurements acquired through mechanical testing. In this study we use tomography data, where the resolution determines the scale at which we look at the material. At a coarse scale we see fibre bundles, whereas at a more fine scale it is possible to see individual fibres. Our segmentation method, based on a dictionary of image patches, plus an additional tracking to extract the fibre trajectories can deal with low quality scans, which opens up for in-situ studies where the scan time needs to be short.