Advanced Characterization Techniques for Quantifying and Modeling Deformation Mechanisms: Session II
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

Monday 2:00 PM
February 27, 2017
Room: 33C
Location: San Diego Convention Ctr

Session Chair: Thomas Bieler, Michigan State University; Xavier Sauvage, Normandy University

2:00 PM  Invited
Atomic Scale Investigation of Co-deformation and Mechanical Mixing in Severely Deformed Multiphase Structures: Xavier Sauvage1; 1Normandy University
    Large plastic deformation of multiphase materials leads to unique microstructures. Beyond the influence of the deformation path, the ability of different phases to co-deform is a critical parameter controlling the final structures and the related properties. It is proposed to review in this presentation few systems to illustrate the behavior of ductile/ductile (like Cu/Fe) or ductile/brittle (like Al/Ti or Al/metallic glass) phase mixtures to show how plastic instabilities and mechanical mixing induced by severe plastic deformation could lead to unique nanoscaled structures. The underlying physical mechanisms will be discussed on the basis of high resolution transmission electron microscopy and atom probe tomography data.

2:20 PM  
Strain Localization Structures in Textured Magnesium AZ31 under Reversed Loading via Multi-scale Digital Image Correlation: Enver Kapan1; Nima Shafaghi1; Sevinç Uçar1; Cahit Aydıner1; 1Bogazici University
    In favorable crystallographic texture and loading path combinations, Magnesium AZ31 deformation is dominated by twinning. A marked component of the material behavior in this regime is the spatial distribution of the accommodated strain: there is sharp strain localization at every length scale including macroscopic, stemming from an abrupt propagation of twinning events across neighboring grains (e.g., Aydiner and Telemez, Int. J. Plas. 2014(56), p. 203). Strain mapping with digital image correlation (DIC) has been instrumental in bridging length scales and highlighting strain heterogeneity levels in this material. With a multiple-optical-axis DIC apparatus, strain maps are obtained with macroscopic and microscopic resolution for the full field. For the sharp rolling texture, strain heterogeneity patterns can be directly interpreted on the micro-mechanisms of the abundant orientation. These patterns are presented at representative points of the reverse-loading cycle and interpreted with respect to operative twin and slip mechanisms.

2:40 PM  
Kink Band Propagation during Plastic Deformation of Bulk Metallic Nanolaminates: Thomas Nizolek1; Nathan Mara2; Rodney McCabe3; Irene Beyerlein4; Jaclyn Avallone1; Tresa Pollock1; 1Materials Department, University of California Santa Barbara; 2Institute for Materials Science and the Center for Integrated Nanotechnologies, Los Alamos National Laboratory; 3Materials Science and Technology Division 8, Los Alamos National Laboratory; 4Mechanical Engineering Department, University of California Santa Barbara
    Kink band formation is a type of shear localization that occurs in an astounding variety of anisotropic materials including low-symmetry single crystals, fiber composites, oriented polymers, and biological materials. While this phenomena is associated with large load drops and occurs dynamically in many systems, stable kink band growth has been observed during uniaxial compression of accumulative roll bonded (ARB) Cu-Nb nanolaminates. This has allowed kink band formation to be studied using in situ SEM compression tests and digital image correlation (DIC) strain mapping of bulk compression specimens. It is found that kink bands initiate at specimen corners, propagate through specimens at high stress (>1 GPa) under a rising load, and induce significant accommodation strain fields in the surrounding material. Revisions to existing kink band models are proposed to enable accurate prediction of mechanical behavior and energy dissipation during kink band formation.

3:00 PM  
A Novel In Situ TEM Technique: High Strain Rate Tensile Testing in the Dynamic TEM: Thomas Voisin1; Michael Grapes1; Yong Zhang1; Nicholas Lorenzo2; Jonathan Ligda2; Brian Schuster2; Tian Li3; Melissa Santala3; Geoffrey Campbell3; Timothy Weihs1; 1Johns Hopkins University; 2Army Research Laboratory; 3Lawrence Livermore National Laboratory
    Current TEM characterization of metals deforming at high strain rates is limited to pre and post-test observations. However, observing dislocation slip and twinning in situ can improve our ability to understand and accurately predict the dynamic properties of metals. We describe a novel technique developed to address this need. Specimens are fabricated from bulk samples using femtosecond laser machining and ion milling, and they are loaded in tension up to 4 x 10^3/s using a novel TEM straining stage. Rapid defect nucleation and motion are captured using the Dynamic TEM at the Lawrence Livermore National Laboratory in which we record 9-frames movies with a delay between frames ranging from 50ns to 5us. The most recent DTEM observations on pure copper and magnesium alloys will be presented, and and they will be compared with results from in situ straining experiments performed at quasi-static strain rates in a conventional TEM.

3:20 PM Break

3:40 PM  
Deformation and Strengthening Mechanisms in AISI 321 Austenitic Stainless Steel under both Dynamic and Quasi-static Loading Conditions: Ahmed Tiamiyu1; Akindele Odeshi1; Jerzy Szpunar1; 1University of Saskatchewan
    The mechanical response of AISI 321 austenitic stainless steel under compressive loads at strain rates of 6600 s-1 and 4.2 x 10-3 s-1 were studied using the split Hopkinson pressure bar and Instron R5500 mechanical testing system respectively. Specimens subjected to quasi-static compression showed lower yield strength and higher strain hardening capacity than the dynamically impacted specimen. High-resolution electron backscattered diffraction (HR-EBSD) study revealed that precipitation of nano-sized carbide and evolution of strain-induced martensite contributed to strengthening while plastic deformation mechanisms occurred in the specimens by slip and mechanical twinning during deformation under both quasi-static and dynamic loading conditions. The strain-induced phase transformation follows the FCC ɣ-austenite → BCC ά-martensite kinetic path with both phases maintaining the Kurdjumov-Sachs’ {(111)ɣ||(110)ά and <-101>ɣ||<1-11>ά} orientation relationship. A transformed shear band consisting of nano-grains with an average size of 0.28 µm was one of the microstructural features of the dynamically impacted specimen. HR-EBSD analysis revealed that the equiaxed ultra-fine grain structure in the TSB developed by rotational dynamic recrystallization mechanism while dynamic recovery occurred at the interface between the inside and outside of the band. During the deformation under both loading conditions, volume fraction of compression direction (CD)//{110} and CD//{111} increases substantially and slightly, respectively at the expense of CD//{100} fibre texture for the austenitic phase.

4:00 PM  
Study of Homophase Interfaces in Structural Materials by ECCI and EBSD in the SEM: Ivan Gutierrez-Urrutia1; 1National Institute for Materials Science
    Alloy design approaches based on the microstructural control of homophase and heterophase interfaces have recently provided novel alloy design concepts in different alloy systems. In particular, approaches based on the control of homophase interfaces such as dislocation patterning induced by strain localization phenomena, twin interfaces and shear bands have led to high performance steels and Ti alloys. Here, we investigate the role of homophase interfaces on the deformation and strain-hardening mechanisms of austenitic steels and bcc-Ti-Mo alloys by correlative EBSD and ECCI methods in the SEM. Texture and solute effects on the formation and propagation of such homophase interfaces will be discussed. Another relevant aspects such as the plastic accommodation of the evolving interfaces will be also addressed. References: I. Gutierrez-Urrutia et al., STAM 17 (2016) 29-36, I. Gutierrez-Urrutia et al., STAM 17 (2016) 220-228