Advanced Thermo-mechanical Characterization of Materials with Special Emphasis on In Situ Techniques: In Situ Techniques III
Sponsored by: TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Nanomechanical Materials Behavior Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Amit Pandey, LG Fuel Cell Systems Inc.; Sanjit Bhowmick, Hysitron; Jeff Wheeler, ETH Zurich; María Teresa Pérez Prado, IMDEA Materials Institute; Robert Wheeler, MicroTesting Solutions LLC; Josh Kacher, Georgia Tech

Tuesday 8:30 AM
February 28, 2017
Room: 32A
Location: San Diego Convention Ctr

Session Chair: Jon Molina, IMDEA- Spain; Sanjit Bhowmick, Hysitron, Inc.

8:30 AM  Keynote
Elevated Temperature Mechanical Properties of Three Component Nanolaminate Thin Films: David Bahr1; Rachel Schoeppner1; Jeffery Wheeler2; 1Purdue University; 2ETH Zurich
    Nano-scale metallic multilayers can contain both Incoherent and coherent interfaces. Maintaining strength at and after elevated temperature service is a concern for these nanostrcutures. A Cu/Ni/Nb tri-layer system with both incoherent and coherent interfaces was less sensitive to elevated temperature softening than a bi-layer system. The decrease in strength was minimized as individual layer thicknesses decreased. To determine if this was a result of Cu-Ni alloying, an additional bi-layer system of CuNi/Nb was tested to simulate fully alloying of the Cu and Ni layers. Testing using both elevated temperature testing and in situ micopillar compression was used to explore the possible strengthening mechanisms. In both material systems there was an increase in room temperature strength after annealing, which has not been seen in other multilayer systems. By choosing the layer thickness and material selection of the multilayer films, mechanical properties can be specifically tailored.

9:10 AM  
In-situ Imaging and Diffraction Studies of Shear Band Nucleation and Propagation in Metallic Glass and Composites: Jia Chuan Khong1; Jiawei Mi1; 1University of Hull
    In this work, we studied in situ the nucleation and propagation of shear bands under tension in a ZrTi bulk metallic glass and a composite. A micrometre-size semi-circular or circular stress concentrator was introduced onto the miniature dog-bone shaped samples to facilitate the initiation of shear bands. This arrangement allows the nucleation and propagation of shear bands under tensile loads to be controlled in a quasi-static manner, and then studied in situ systematically using electron imaging. To measure the local stresses/strains in front of the shear bands at different loads, samples were tested under the identical conditions at a synchrotron X-ray beamline. Diffraction patterns were acquired at the locations/paths where shear bands were observed, and the local stresses/strains field were calculated based on the acquired diffraction patterns. The imaging and diffraction studies provide complimentary information on how shear band propagation is controlled by the local stress field ahead.

9:30 AM  Invited
Plasticity and Time Dependent Stress Relaxation in FCC Nanowires: Horacio Espinosa1; Rajaprakash Ramachandramoorthy1; Yanming Wang2; Rodrigo Bernal1; Amin Aghaei2; Gunther Richter3; Wei Cai2; 1Northwestern University; 2Stanford University; 3Max Planck Institute
    In this work, we investigate the cyclic stress-strain behavior of penta-twinned silver nanowires using in situ SEM and TEM tests. Loading and unloading cycles reveal hysteresis with increasing strain and the existence of a very strong Bauschinger effect. TEM observations reveal that these processes occur due to the penta-twinned structure and reversible dislocation activity. While plasticity through surface nucleation of stacking fault is fully reversible, the plastic deformation is only partially reversible as its accumulation result in dislocation-dislocation interactions leading to sessile dislocation reactions. We also investigate the time-dependent behavior of single crystal silver nanowires held at a constant strain. Initially, the stress in the nanowire relaxes due to the formation of a few stacking faults. Surprisingly, after few hours of holding the nanowire at constant strain, it ruptures abruptly. Using phase field simulations and numerical modeling, we show that surface undulations grow through stress-assisted diffusion leading to rupture.

10:00 AM Break

10:20 AM  
In-situ Neutron Diffraction Analysis for Dynamic Ferrite Transformation Behavior in Low-carbon Steels: Akinobu Shibata1; Yasunari Takeda1; Wu Gong1; Stefanus Harjo2; Takuro Kawasaki2; Nobuhiro Tsuji1; 1Kyoto University; 2Japan Atomic Energy Agency
    A thermomechanical processing, i.e., precisely controlled deformation and heat treatment, has been practically used to make large steel products. Nowadays, the process utilizing dynamic ferrite transformation, which occurs during plastic deformation of austenite, has been received much attention as a new thermomechanical processing because ultrafine-grained ferrite structures can be easily achieved through dynamic ferrite transformation. In order to reveal dynamic ferrite transformation mechanism and establish the new type of thermomechanical processing based on theoretical aspects, we have developed a thermomechanical processing simulator for in-situ neutron diffraction analysis at elevated temperature. In this presentation, we report dynamic ferrite transformation behavior in low-carbon steels analyzed by the in-situ neutron diffraction technique. We found that dynamic ferrite transformation surely occurred during deformation of austenite and the lattice constant of dynamically transformed ferrite decreased with the progress of transformation. The results suggest that partitioning behavior of alloying elements changed during dynamic transformation.

10:40 AM  
In Situ 4D Tomographic Examination of Semi-solid Indentation Behaviour in Ni and Co Based Alloys: Mohammed Azeem1; Chedtha Puncreobutr2; Robert Atwood3; Rahman Khandaker4; David Dye4; Peter Lee1; 1Manchester University; 2Chulalongkorn University; 3Diamond Light Source; 4Imperial College London
     Investigating the semi-solid deformation behavior in metallic systems is critical for understanding defect formation and identifying temperature-pressure windows for tailoring the microstructure. In indentation of Al based alloys in semi-solid state, granular flow and liquation assisted cracking are the primary mechanisms that dictate the microstructure evoluton. However, it remains unknown if similar mechanisms operated in semi-solid state in Ni and Co based alloys. Here we use a bespoke tomography rig equipped with a high temperature environmental cell and exclusively designed high x-ray contrast Ni and Co based alloys with ~300 μm globular gains to investigate the response of microstructure to indentation in semi-solid state. The α-Ni and α-Co grains were found to be remarkably soft with indenter slicing through almost all the grains in its path. In some instances the inverter was found to cut through free-floating grains. The associated morphological aspects and possible deformation mechanisms will be discussed.

11:00 AM  
In-situ Micro-Laue Diffraction and HR-EBSD Investigation to Understand the Microstructure-deformation Interactions in Dual-phase Titanium Alloy, Ti6242, Using Micro-pillar Compression: Tea-Sung Jun1; Xavier Maeder2; Gaylord Guillonneau3; Johann Michler2; Finn Giuliani1; T Ben Britton1; 1Department of Materials, Imperial College; 2EMPA; 3Laboratoire de Tribologie et Dynamique des Système, Université de Lyon
    Dual phase titanium alloys are widely used in aerospace applications since their microstructures can be thermomechanically tailored to optimise desired performance. However, our knowledge of the role of individual microstructural components on the deformation of these alloys remains largely underexplored. In this talk, we explore the role of alpha-beta boundaries on the local plastic behaviour in single and dual-phase colonies, through micro-pillar compression, using both in situ micro-Laue diffraction and HR-EBSD experiments. Our pillars have been aligned to primarily activate single <a> basal or prismatic slip in the alpha phase of Ti6242. The morphology, volume fraction and orientation of the alpha and beta phases are found to change the strength, local deformation patterning and slip character.

11:20 AM  
In Situ X-ray Diffraction Study of Strain Path Change Effects in Al-5wt% Mg (AlMg5) Using a Miniaturized Multiaxial Deformation Machine: Karl Sofinowski1; Maxime Dupraz2; Steven Van Petegem2; Helena Van Swygenhoven1; 1Paul Scherrer Institut & EPFL; 2Paul Scherrer Institut
     A novel miniaturized multiaxial deformation machine for measuring strain path changes in situ with x-ray diffraction is presented. The machine is designed to measure cruciform samples at various load ratios and can be implemented in a scanning microscope. In situ x-ray diffraction experiments on ultra-fine grain Al-5wt% Mg are presented. The cruciforms are prepared using picosecond pulsed laser ablation to mill the gauge section to 50 μm [Mat Letters 160(2015)589]. Uniaxial, equibiaxial and load path changes have been performed, as well as uniaxial dogbone samples for comparison. For all load paths, the characteristic strain bursts of the Portevin Le Chatelier (PLC) can be observed. The diffraction patterns show a distinct response to the PLC effect. Additionally, the final microstructure of the deformed samples are compared to the initial microstructure using transmission electron microscopy (TEM) and discussed in respect to the lattice strain evolution measured during the test.

11:40 AM  
Characterizing Thermal- and Moisture-induced Glass Transitions Using Nanoindentation-based Dynamic Mechanical Analysis: Joseph Jakes1; 1USDA Forest Products Laboratory
    Nanoindentation-based dynamic mechanical analysis (nanoDMA) is needed to assess glass transitions from small micron-scale volumes of materials, such as individual components in composite materials or wood cell walls. Protocols have been developed using a Berkovich nanoindentation probe to measure viscoelastic properties of polymers across four decades of frequency. During the experiment the material temperature can be controlled between 25 and 250 degrees Celsius and the ambient relative humidity controlled between 0 to 95%. The protocols were validated by comparing the thermal-induced glass transitions measured by nanoDMA to those measured by conventional single-cantilever dynamic mechanical analysis for cast acrylic, polystyrene, nylon 6,6, and poly(ether ether ketone) bulk polymers. The utility of the developed protocols was then demonstrated by characterizing the moisture-induced glass transitions in wood cell walls.