Deformation and Transitions at Interfaces : Poster Session
Sponsored by: TMS Functional Materials Division (formerly EMPMD), TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Thomas Bieler, Michigan State University; Rozaliya Barabash, OakRidge National Lab; Shen Dillon, Universe of Illinois; Jian Luo, University of California, San Diego; Doug Spearot, University of Florida

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

L-43: A Hybrid Fast Fourier Transform Based Elasto-Viscoplastic Formulation: Jaspreet Nagra1; Abhijit Brahme1; Ricardo Lebensohn2; Raja Mishra3; Kaan Inal1; 1University of Waterloo; 2Los Alamos National Laboratory; 3General Motors Research and Development Center
    In the present work, a “hybrid” full field elasto-viscoplastic formulation is proposed that combines the finite strain Asaro-Needleman formulation with a computationally efficient fast Fourier transformation (FFT) based crystal plasticity model. The proposed hybrid model is calibrated using experimental uniaxial tensile test of AA5754 and is then used to predict response for equi-biaxial tension and plane strain tension. The predicted stress-strain and texture results show a good agreement with experimental measurements. For each strain path, the CPU time taken by the proposed hybrid model is compared with EVPFFT model. The proposed hybrid model is then used to predict forming limit diagram (FLD) by incorporating M-K formulation into the model. The predicted FLD for AA5754 and AA3003 are compared with experimental measurements. The proposed hybrid model showed significant time improvement than EVPFFT along with good agreement with experiment observations. The effects of grain morphology on FLD predictions are also presented.

L-44: Dislocation and Twin Interactions with Specific Ag/Cu Interfaces: Ben Eftink1; 1University of Illinois
    Interface structure, controlled by processing conditions, was found to contribute to the bulk mechanical properties of a Ag/Cu eutectic. To account for this, dislocation and deformation twin interactions with specific Ag/Cu interface types, cube-on-cube and incoherent twin, were investigated by in situ TEM straining experiments and molecular dynamics simulations. It was found that whether an interface provided a weak or strong barrier to dislocations or twins is dependent on the size of the residual dislocation left at the interface to communicate strain across the interface.

L-45: Controlling the Deviation of Twins in Inconel 600 Alloy by Hot Rolling: Sandeep Sahu1; Shashank Shekhar1; Pallavi Gupta2; 1Indian Institute of Technology Kanpur; 2IIT Roorkee
    Twinning related ‘grain boundary engineering’ is a well-established technique in order to improve functional and mechanical properties. However, even in a material having high fraction of twin boundaries, property like resistance to intergranular degradation decreases when the deviation (from the exact disorientation) in twin boundaries increases. Hence, the objective of the present work was to achieve high coincidence site lattice (CSL) boundaries fraction with less deviated twin boundaries. Low strain (4-24%) was imparted to Inconel 600 alloy by hot rolling in order to minimize the generation of highly deviated twins. Deformed material was given a short annealing treatment of 10 minutes to control grain growth. The results showed the increment in total CSL fraction (3≤Σ≤29) as high as 77% having a dominant fraction from twin (Σ3) boundaries (64%). Also, 93% of Σ3 boundaries were found to lie within a very low deviation value of 0.87°.

L-46: Correlation of Bendability of CuAg Conductors with Their Tensile Properties: Rongmei Niu1; Ke Han1; Jun Lu1; Doan Nguyen1; 1National High Magnetic Lab
    During the manufacture of various coils, conductor wires with rectangular-shape cross section are wound to small diameter (less than 15 mm). The small diameter results in large bending strain due to the large wire thickness. In our study, the maximum bending strain even exceeded the elongation of CuAg conductor wires, which may cause premature failure. In some applications, even smaller bending diameter is requires, which then leads to even higher bending strain in conductor. Therefore we conducted ex-situ bending test on CuAg wire to compare and analyze the microstructure and strain evolution near the inner and outer side surfaces. The bendability is directly related to the ductility and work hardening of CuAg, and is restricted by the local thinning or necking.

L-47: Deformation Mechanisms in Ti/TiN Multi-layered Thin Films: Tarang Mungole1; Bilal Mansoor2; Georges Ayoub3; David Field1; 1Washington State University; 2Texas A and M University, Doha, Qatar; 3American University of Beirut
    Deformation behavior of metal-ceramic multi-layered systems is not fully understood. Metal-ceramic multi-layered thin film systems comprising of alternating layers of Ti and TiN were fabricated using a physical vapor deposition technique on a (100) type Si wafer. Samples with different period thicknesses of Λ = 20 nm, Λ = 10 nm and Λ = 5 nm were produced. Films of pure Ti and pure TiN were fabricated as reference samples. Nano-indentation revealed that hardness for Λ = 20 nm sample was higher than predicted by the rule-of-mixtures, while Λ = 10 nm and Λ = 5 nm samples were in its agreement. Atomic force microscopy revealed grain boundary sliding of ~ 2 nm in ~ 30 nm sized grains in pure Ti sample after micro-indentation. Details of the deformation mechanisms at the interfaces of the multi-layered systems assessed by microscopic observations will also be presented.

L-48: Development of Synthetic Driving Force Methods in HCP Crystals and Comparison to Existing Techniques: Matthew Guziewski1; Shawn Coleman2; Ian Bakst1; Mark Tschopp2; Christopher Weinberger1; 1Colorado State University; 2Army Research Lab
    Synthetic driving forces are an established method for simulating grain growth and calculating mobilities in molecular dynamic simulations. However, current approaches have only been implemented for FCC and BCC materials. This work expands the implementation of the Energy Conserving Orientational (ECO) force developed by Ulomek et al. and the orient driving force developed by Janssens et al. to the HCP crystal structure. Simulation results for these two methods are compared to shear driven grain boundary motion, revealing good agreement between the methods in both grain boundary velocity and structural behavior.

L-51: Effect of Deformation Heterogeneity of TWIP Steels on Near Boundary Twinning Behavior Using Crystal Plasticity Simulation: Jaimyun Jung1; Jae Ik Yoon1; Jung Gi Kim1; Marat Latypov2; Jin You Kim3; Hyoung Seop Kim1; 1POSTECH; 2Georgia Tech; 3POSCO
    A full-field calculation on the mechanical twinning of hot-rolled TWIP steel during tensile deformation is investigated under a crystal plasticity framework. Microstructures are first observed through electron backscatter diffraction (EBSD) technique to obtain data to construct a statistically equivalent synthetic microstructure through a synthetic microstructure building software. Afterwards, grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of microstructural volume element under tensile deformation. In particular, twinning behavior near grain boundaries are observed to identify the effect of strain heterogeneity. The simulated results shed light on the general trend in micromechanical twinning behavior correlated with orientation, change in orientation and grain interactions during the course of tensile deformation.

L-52: Effect of Electric Fields on Grain Boundary Characteristics in Ceramics: Wei Qin1; 1University of California, Davis
    Recent studies on electric field assisted sintering (EFAS) techniques showed that improved sintering kinetics were achieved with applied electric fields. The understanding of the role of electric field on interface behavior between grains is crucial. The present research utilized electron microscopy techniques to study grain boundaries in polycrystalline materials as a function of the applied electric field during processing. The work explores the effect of electric field on grain boundary formation and structures as well as grain growth behavior and microstructural evolution. Our first results on flash sintered yttria-stabilized zirconia (YSZ) demonstrated enhanced diffusion kinetics across grain boundaries. Our ongoing work includes using electron holography, electron energy loss spectroscopy and orientation imaging in transmission electron microscopy to investigate the grain boundary structure and misorientation on YSZ and MgAl2O4 spinel annealed in the presence and absence of an externally applied electric field.

L-53: Grain Boundary Mechanisms in Nickel-based Superalloys: John Rotella1; Martin Detrois2; Sammy Tin2; Michael Sangid1; 1Purdue University; 2Illinois Institute of Technology
    Mechanical behavior of structural materials are governed by their grain boundaries. Annealing twins have been shown as favorable boundaries to enhance strength and ductility. Through the process of Grain Boundary Engineering (GBE), we have the ability to tailor the volume fraction of the annealing twins to improve the mechanical behavior of the material. In this work, concurrent electron backscatter diffraction and digital image correlation will be used to study the heterogeneous strain of GBE nickel-based superalloys. Specifically, superalloys with various grain sizes and contents of annealing twins are cyclically loaded to determine the role of microstructure on strain evolution and accumulation.

L-55: In-situ EBSD Study on Recrystallization Nucleation in Deformed Al: Guilin Wu1; 1Chongqing University
    During recrystallization annealing of deformed metals, new strain-free crystals develop in the deformed matrix. This process is described as recrystallization nucleation. Nucleation affects the microstructure and texture and as a consequence the mechanical properties of recrystallized metals. The mechanism of recrystallization nucleation has not been fully understood although tremendous post mortem observations of nuclei have been carried out over the past decades. One of the reasons is that once a nucleus is formed in a region in the deformed matrix the deformed microstructure corresponding to that region will disappear so that the direct evidence of nucleation process is lost. In this work, we carried out in-situ electron backscatter diffraction (in-situ EBSD) study in a scanning electron microscope (SEM) to follow the microstructural and orientational evolutions during deformation and then annealing of a high purity Al sample. This means that the orientations of a given region in the sample were measured under three sample states, namely initial undeformed state, deformed state and annealed state. This type of experiments enabled us for the first time to analyze (i) the orientation change for a given region before and after the nucleation event (namely the relationship between the orientation of a newly formed nucleus and the orientation of its corresponding region in the deformed state) and (ii) the relationship between the orientation of the nucleus and the orientation of the same region in the initial undeformed state. The analysis generated new results that provide new insight into the mechanism of recrystallization nucleation. Particular attention was paid to the orientation relationships with rotation axes of <111>, which lead to a discussion on the formation mechanism of the frequently observed 40°<111> orientation relationship between nuclei and deformed matrix in fcc metals.

L-56: Influence of Deformation Processing on the Superelastic Behavior of NCAXB Alloys: Cheng Zhang1; Kenneth Vecchio1; 1Department of NanoEngineering and Materials Science and Engineering Program, University of California, San Diego
    Fe-based superelastic alloys are of considerable interest as a cost-effective functional material. To achieve superelasticity in these materials, a certain combination of matrix strengthening, precipitation hardening, and microstructural texturing is required. In heavily cold-rolled and solutionized Fe-Ni-Co-Al-X-B (X= Ta, Cr) polycrystalline superelastic alloys, texture development was evaluated by EBSD, and the fraction of low-angle boundaries was determined. Tensile tests show that texture and the fraction of low-angle boundaries affect the superelasticity of the samples, and are discussed in terms of their effect on deformation mechanisms. The microstructure evolution of grain boundaries was investigated before and after tensile tests, especially in the most strongly-textured samples, and the role that boron plays is examined. Differences in the behavior and properties of the Ta and Cr containing alloys will be compared, with advantages and disadvantages of each discussed.

L-57: Interaction of Grain Boundaries with Nano-clusters in Immiscible Alloys: R. K. Koju1; M. Rajagopalan2; K. A. Darling3; L. J. Kecskes3; K. N. Solanki2; Yuri Mishin1; 1George Mason University; 2Arizona State University; 3US Army Research Laboratory
    We report on molecular dynamics simulations and in-situ TEM experiments of curvature-driven grain boundary motion and thermal stability in copper-tantalum alloys with and without coherent Ta-rich nano-clusters. The TEM observations validate that the clusters drastically reduce the boundary mobility by the Zener mechanism and resist coarsening along with the Cu matrix with the increase in temperature. The boundary can eventually detach from an array of clusters by an unzip mechanics, or become permanently pinned. Grain boundary motion in a random Cu-Ta alloy exhibits a dynamic instability whereby it experiences less resistance if it moves fast and more resistance if it moves slowly. In the latter case, Ta grain boundary diffusion causes a segregation or precipitation of clusters, which in turn make the motion even slower. Consequences for thermal stability and local microstructural changes of immiscible Cu-Ta alloys on the unique un-conventional mechanical properties are discussed.

L-58: Interface Controlled Work Hardening Ability in Ultrafine-grained Ti-6Al-4V Alloy with Bimodal Microstructure: Yan Chong1; Tilak Bhattacharjee1; Ruixiao Zheng1; Tsuji Nobuhiro1; 1Kyoto University
    In metallic materials the increase of yield strength with grain refinement is usually accompanied by the loss of uniform elongation, which is a so-called trade-off relationship of strength and ductility. Such a relationship was also found in the titanium alloy Ti-6Al-4V with equiaxed microstructures, in which the uniform elongation of ultrafine-grained (UFG) equiaxed microstructures (d≤1μm) decreased to only ~1%. However, the uniform elongation can be restored to 5~8% simply by transforming the UFG equiaxed microstructure into UFG bimodal microstructure via annealing in the two phase region followed by water quenching. In-situ tensile deformation in TEM indicated that the improved uniform elongation in the UFG bimodal microstructure was attributed to the introduction of interfaces between equiaxed α grain (αp) and transformed β area (βtrans). In the early stage of deformation, dislocations were emitted from the αp/βtrans interface in the bimodal microstructure while formed inside the α grains in the equiaxed microstructure.

L-59: Mechanical Characterization of Ti-6Al-4V Titanium Alloy at Multiple Length Scales Using Spherical Indentation Stress-strain Measurements: Jordan Weaver1; Surya Kalidindi2; 1Los Alamos National Laboratory; 2Georgia Institute of Technology
    Recent advances in spherical indentation stress-strain protocols and analyses have demonstrated the capability for measuring reliably the mechanical responses in polycrystalline metals at different length scales (sub-micron to several hundreds of microns). These advances have now made it possible to study systematically the mechanical behavior of a single material system at different length scales. We report on spherical indentation stress-strain measurements with different indenter sizes (microns to millimeters) on Ti-6Al-4V (Ti-64) which capture the mechanical response of single phase alpha-Ti-64, single colony (alpha-beta), few colonies, and many colonies of Ti-64. The results show that the average response (indentation modulus and yield strength) from multiple indentations remains relatively unchanged from single phase alpha to many colonies of Ti-64, while the variance in the response decreases with indenter size. The work-hardening response in indentation tests follows a similar behavior up to indentation zones of many colonies, which shows significantly higher work-hardening rates.

L-60: Non-uniform Magnetostress in Magnetic Shape-memory Alloys: Anthony Hobza1; Peter Müllner1; 1Boise State University
    A magnetic field generates a stress state in a magnetically anisotropic material when the magnetic field is not parallel to the easy axis of magnetization. At interfaces, the orientation of the easy axis changes abruptly and so does the stress state. In general, discontinuities of the stress state violate the mechanical equilibrium conditions resulting in a net force distributed along the grain boundary. In the case of a twin with two parallel twin boundaries, the net forces of the two twin boundaries result in a net torque. We measured this torque by subjecting twinned Ni-Mn-Ga magnetic shape memory alloy single crystals to a magnetic field. The torque increased with increasing magnetic field and with increasing twin width. We discuss implications of the inequilibrium stress for the magneto-mechanics of magnetic shape memory alloys such as fracture and fatigue.