Advanced Characterization Techniques for Quantifying and Modeling Deformation Mechanisms: Session IV
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 2:00 PM
February 28, 2017
Room: 33C
Location: San Diego Convention Ctr

Session Chair: Aaron Stebner, Colorado School of Mines; David Fullwood, Brigham Young University

2:00 PM  Invited
Digital Image Correlation Using Forescatter Detector Images for the Study of Transformation in TRIP Steel: David Fullwood1; Shamoon Irfan2; Jeff Cramer1; Tyler Mathis1; Derrik Adams1; Michael Miles1; Eric Homer1; Tyson Brown3; Robert Kubic3; 1Brigham Young University; 2The Northcap University; 3General Motors
    Improved models of retained austenite transformation in trip steels require experimental data of local strain and transformation evolution. Microscopy tools, such as electron backscatter diffraction (EBSD), that can be used to monitor transformation at the relevant length-scale are often incompatible with digital image correlation (DIC) techniques that are required to determine local deformation. In this paper, the viability of using forescatter detector (FSD) images as the basis for the DIC study is investigated. While the method does not give subgrain resolution, the data is easy to obtain and provides a natural set of complementary information for the EBSD analysis. Results are presented for tensile tests of an 1180 trip steel.

2:20 PM  
In-situ Experiments to Capture Rapid Microstructural Evolution and Phase Transformation of Titanium during Dynamic Loading: Benjamin Morrow1; David Jones1; Paulo Rigg2; Ellen Cerreta1; 1Los Alamos National Laboratory; 2Washington State University
    Under sufficient stresses, such as during dynamic loading, titanium experiences a phase transformation from hcp alpha phase to hexagonal omega phase. Omega phase is often retained in the microstructure after unloading, and has a strong influence on subsequent mechanical properties. Simulations suggest there are multiple pathways and underlying mechanisms for this transformation. Due to the incredibly short timescales involved, experimental measurements for model validation have been difficult. However, new capabilities at the Advanced Photon Source have enabled diffraction measurements during plate impact experiments to study the evolution of titanium during transformation. These high-rate data allow us to probe the mechanism and kinetics of phase transformations in new ways. Recent results will be presented and compared to post-mortem characterization of soft-recovered shocked specimens. TEM and EBSD are used to further characterize and quantify microstructural features, including alpha-phase twinning and omega-phase variants formed during deformation, and determine likely mechanisms and pathways.

2:40 PM  
In-situ Structural and Mechanical Characterization of ThCr2Si2-structured Superelastic Intermetallic Compounds: Keith Dusoe1; Ian Bakst2; John Sypek1; Gil Drachuck3; Paul Canfield3; Christopher Weinberger2; Seok-Woo Lee1; 1University of Connecticut; 2Drexel University; 3Iowa State University
    Crystalline, superelastic materials typically exhibit large recoverable strains through a reversible phase transition between martensite and austenite phases that are associated with twinning and de-twinning processes. Applicable to various alloys, ceramics and intermetallic compounds, this reversible transition serves as a general mechanism for superelasticity. In our recent work, a new superelasticity mechanism has been observed in a novel ternary intermetallic compound, CaFe2As2. Of the ThCr2Si2-type intermetallic compounds, this material exhibits a reversible phase transition between tetragonal and collapsed tetragonal phases under compression. In this presentation, two very different ThCr2Si2 structured intermetallic compounds, LaRu2P2 and CaFe2As2, are compared. Single crystal solution growth, in-situ micropillar compression, in-situ X-ray diffraction, and density functional theory calculation was used to elucidate the unique superelasticity mechanisms at work. We will also discuss the potential applications of these materials as cryogenic linear actuators and switching devices which can operate in extremely cold environments.

3:00 PM  
In-situ EBSD Analysis and Crystal Plasticity FE Simulations in a CP Titanium Sheet: Joo-Hee Kang1; Ji Hoon Kim2; Chan Hee Park1; Chang-Seok Oh1; 1Korea Institute of Materials Science; 2Pusan National University
    The alpha titanium alloys exhibit unique anisotropic mechanical behavior due to the activation of multiple slip systems and twinning. Therefore the quantitative analysis of microstructure and texture is needed for understanding of deformation mechanism. In this study, the effect of initial grain size and tensile direction on the deformation behavior in CP titanium was analyzed and predicted using in-situ EBSD analysis and crystal plasticity simulations. The initial microstructure and orientation obtained by EBSD were used to develop crystal plasticity finite element model. The EBSD results were obtained during the tensile deformation in the direction of RD and TD. Also, the deformation behavior was evaluated in the specimen with different grain size. They were compared with the calculated ones by crystal plasticity finite element simulations. Prismatic slip system was dominant, whilst other slip systems and twinning were operating. Twinning was suppressed in the specimen with smaller grain size.

3:20 PM Break

3:40 PM  Invited
Mechanics of Phase Transformation in Shape Memory Alloys: A Coupled High-energy X-ray Diffraction and Forward Modeling Approach: Aaron Stebner1; Harshad Paranjape1; Ashley Bucsek1; 1Colorado School of Mines
    High energy diffraction microscopy (HEDM), an X-ray based non-destructive technique, enables the characterization of microstructure (grain centroid, size, orientation) and deformation (lattice strain), which is essential to elucidate the mechanics of phase transformation. We present a novel characterization approach that integrates HEDM-based in-situ microstructural characterization with forward modeling of diffraction patterns from martensite microstructures to quantify the micro mechanics of phase transformations. The forward modeling component enables prediction of martensite microstructures that cannot be practically reconstructed using HEDM. Using this approach, we explore the SMA mechanics in two scenarios. First, we discuss the crystal orientation and boundary effects on the stress-induced martensite microstructures in superelastic NiTi single and oligocrystals. Second, we explore the mechanics of detwinning and reorientation in martensitic NiTi SMAs. This coupled diffraction-modeling approach can be extended to other phase transforming and twinning materials.

4:00 PM  
Characterizing the Boundary Lateral to the Shear Direction of Deformation Twins in Magnesium: Yue Liu1; Jian Wang2; Rodney McCabe1; Carlos Tomé1; 1Los Alamos National Lab; 2University of Nebraska, Lincoln
    With regard to the 3D nature of deformation twins, twin propagation and growth involves motion of twin boundaries in three characteristic directions: normal to the twin plan, in the twin shear direction and lateral to the twin shear direction. Twin boundaries associated with twin growth along the first two directions have been extensively studied. However, the atomic structures and motion mechanisms of twin boundaries lateral to the shear direction of the twin has not been identified at the atomic level although they necessarily control the lateral growth of the twin. Using high-resolution transmission electron microscopy and atomistic simulations, we analyzed and characterized the lateral boundary of {0 -1 1 2} twins in magnesium. We find it to be composed of coherent twin boundaries and semi-coherent twist prismatic-prismatic {2 -1 -1 0} boundaries. This structure potentially has significant consequences on the 3D growth behavior of deformation twins in hexagonal materials.

4:20 PM  
Explicit Modeling of Twin Lamellae in AZ31 Using a Crystal Plasticity Finite Element Approach: Milan Ardeljan1; Irene Beyerlein2; Marko Knezevic1; 1University of New Hampshire; 2Los Alamos National Laboratory
    Deformation twinning is known to be an influential deformation mechanism governing the mechanical response and microstructure evolution in low symmetry metals. In this work we present a detailed analysis of twin nucleation and propagation in magnesium alloy-AZ31 using an explicit method for representing the twin morphology and crystallographic twin-matrix orientation relationship within a microstructural full-field crystal plasticity framework. Using this model, we study the stress-strain fields and relative activities of the active deformation slip modes before and after the formation of a twin, within the twin and in the parent grain both close to the twin and away from the twin boundaries. We determine the fields driving expansion in the case of extension twins, which are experimentally reported to have large thicknesses, which oftentimes can span across the entire parent grain. We also predict the fields around contraction twins that would hinder their growth, hence tend to make them thin.

4:40 PM  
Twinning Kinetics and Its Sensitivity to the Strain Rate: Kavan Hazeli1; Owen Kingstedt2; Vignesh Kannan3; Guruswami Ravichandran4; KT Ramesh3; 1University of Alabama in Huntsville; 2University of Utah; 3Johns Hopkins University; 4California Institute of Technology
    This study uses in situ techniques to investigate the effect of strain-rate on the two important aspects of deformation twinning: twin variant selection and twin kinetics. Magnesium (Mg) was selected as a model material to study because its hexagonal close packed structure is closest perfect packing of spheres. Herein the first in situ experimental evidence on the sensitivity of extension twin variant selection to the strain rate in Mg single crystal is presented. It was observed that at the same level of total strain, dynamically compressed specimens contained four extension twin variants and double extension twins while quasi-statically compressed specimens contained only two twin variants. At high strain rate loading twin variant selection was observed to be inconsistent with Schmid-type behavior. This study also investigates the twinning kinetics (growth and thickening) at higher strain rate regime providing the first measurements of twin propagation velocity of first and second-generation twins.

5:00 PM  
Role of Adjoining Twin Pairs on Detwinning under Stress Reversal in HCP Metals: M. Arul Kumar1; Yue Liu1; Irene J Beyerlein1; Rodney McCabe1; Carlos N Tome1; 1Los Alamos National Lab
    Twins in HCP polycrystals nucleate from grain boundaries and propagate to span the entire grain. Twins mostly terminate at grain-boundaries and are referred to as isolated-twins. It is also possible to have adjoining-twin-pairs (ATPs) where twins from neighboring-grains appear to be connected at a shared grain-boundary. Under load reversal, the twins that form during compression can de-twin. The propensity for detwinning is different in the case of isolated twins compared to ATPs. Here we employ automated electron-backscatter-diffraction (EBSD) and full-field Fast Fourier Transform (FFT) modeling to understand the differences in detwinning characteristics under load reversal. The EBSD results show that the tendency for detwinning is less for ATPs compared to isolated-twins. And FFT simulations suggest that the twinning shear transformation of connected twins provides a local strengthening of ATPs at the grain boundaries. This local strengthening can suppress detwinning during reverse loading