Deformation and Transitions at Interfaces : Interfaces in Materials
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

Wednesday 2:00 PM
March 1, 2017
Room: 23B
Location: San Diego Convention Ctr

Session Chair: Shen Dillon, University of Illinois at Urbana-Champaign

2:00 PM  Invited
Plastic Recovery Driven by Interfaces: Ben Eftink1; Owen Kingstedt2; Ao Li3; Izabela Szlufarska3; John Lambros1; Ian Robertson3; 1University of Illinois; 2University of Utah ; 3University of Wisconsin-Madison
    The fundamental processes driving plastic recovery following high strain rate loading of a metallic multilayered system based on the AgCu eutectic is explored using a combination of in-situ straining experiments in the transmission electron microscope, characterization of the deformed microstructure following loading at 103 s-1 and molecular dynamics computer simulation. It will be shown that plastic recovery is dependent on the interface type, cube-on-cube or incoherent twin; loading direction with respect to the interface normal; total plastic strain; and thickness of the Ag-Cu bilayer. This plastic recovery will be shown to be driven by dislocation processes as well as interface restructuring and rearrangement. The decrease in degree of recovery with increasing plastic strain is accounted for by the complexity of the dislocation structures within the layers.

2:20 PM  Invited
Microstructure and Mechanical Behavior of HCP/BCC Bulk Nanolaminate Composites produced by Accumulative Roll Bonding: Nathan Mara1; Daniel Savage2; John Carpenter1; Rodney McCabe1; Thomas Nizolek3; Nan Li1; Sven Vogel1; Marko Knezevic2; Irene Beyerlein1; 1Los Alamos National Laboratory; 2University of New Hampshire; 3University of California, Santa Barbara
    Two-phase nanolaminate thin film composites have demonstrated an unusually broad number of desirable properties, such as high strength, high strain to failure, thermal stability, and resistance to light-ion radiation. Recently we have shown that bi-phase HCP/BCC nanolaminates with individual layer thicknesses approaching 10 nm can be made via severe plastic deformation (SPD) in bulk sizes suitable for structural applications. Mechanical testing of these HCP/BCC nanolaminates shows exceptionally high strength and characterization via a suite of techniques including neutron diffraction, EBSD, and TEM indicates that the crystals are highly oriented. While the cause of these unusual properties can easily be associated with a high density of bimetal interfaces, how the interfaces physically control microstructural evolution and macroscopic properties remains an area of intense research. This presentation highlights our modeling and experimental efforts to understand and link the evolution of the nanostructure, the interface properties, and preferred texture during the SPD process.

2:40 PM  Invited
A Computational Study of the Deformation Response of Cu/Nb Multilayer Composites: Jason Mayeur1; Irene Beyerlein2; 1Los Alamos National Lab; 2University of California, Santa Barbara
    In this talk we present a computational study of the thermomechanical response of Cu/Nb multilayered lamellar composites produced by accumulative roll-bonding (ARB). ARB is a manufacturing process capable of producing bulk multilayered lamellar composites with layer thicknesses ranging from mm to nm. ARB lamellar composites are distinct from those produced by physical vapor deposition in terms of the specimen scale and layer thicknesses that are attainable as well as the predominant texture and heterophase interface character. Both local and nonlocal constitutive frameworks are employed to assess the role of lattice curvature and geometrically necessary dislocations on the deformation response as a function of layer thickness and grain size. The simulation results are compared to recent experimental measurements in an effort to sort out the relative contributions of slip transmission and lattice curvature induced hardening on the overall strength of the materials.

3:00 PM  Invited
Atomic-Scale Studies of Defect Interactions with Homo- and Heterophase Interfaces: Enrique Martinez Saez1; Blas Uberuaga1; Irene Beyerlein1; 1LANL
    The ability of interfaces to dictate the material response resides inherently in their atomic structure, which controls the interactions of dislocations and defects with the interface. We show how dislocations nucleated from defect clusters interact with a heterophase interface in Cu–Nb layered composites. We show how the ability of the interface to absorb vacancy clusters depends on the atomic structure at the interface. We also elaborate on the effect of the atomic structure on the ability of the interface to absorb dislocations as well as vacancy and self-interstitial defect clusters. We study a Kurdjumov–Sachs orientation in a Cu–Nb interface and an asymmetric Σ11 grain boundary in pure Cu. On the one hand, the manner in which dislocations react with the interface depends on the misfit dislocation arrangement, which substantially differs between these two cases. On the other hand, vacancy and self-interstitial clusters are absorbed similarly upon interaction with both structures.

3:20 PM  Invited
Structure and Dynamics at the Cathode/Electrolyte Interfaces in Li-S Batteries: Ying Ma1; 1University of Wisconsin-Eau Claire
    Lithium-sulfur (Li-S) batteries are promising for electrical energy storage. Unlike intercalation compounds, the sulfur cathode undergoes a series of complex electrochemical reactions with substantial structural changes during charge and discharge. Various lithium polysulfides are formed that may shuttle between the electrodes, resulting in capacity loss and poor Coulombic efficiency. To identify the microscopic mechanisms, the structures and dynamics at the cathode/electrolyte interfaces in Li-S batteries were studied using first principles calculations. First, the equilibrium structures of various interfaces between α-sulfur and dimethoxyethane, which is a commonly used electrolyte, were determined. Then, the structural evolution was studied using ab initio molecular dynamics by adding lithium ions at a specific rate that simulates the discharge process. Based on these simulations, the elementary process that leads to the formation of soluable polysulfide was analyzed. Possible strategies that can be used for the rational design of the sulfur cathode with improved performance were proposed.

3:40 PM Break

4:00 PM  Invited
Structure of Semicoherent U-Zr Interfaces.: Elton Chen1; Remi Dingreville2; Chaitanya Deo1; 1Georgia Institute of Technology; 2Sandia National Laboratories
    A quantitative understanding of the compositional and microstructural features dictating fuel/clad heterophase interfaces is necessary for assessing the stability and aging of spent nuclear fuel. Specifically, the presence of misfit dislocations in such semicoherent interfaces play an important role in their physical-mechanical properties. The structure of these interfaces depends on the physical and chemical nature of the contacting phases (including size and symmetry of elementary crystal cells) but also on external factors such as temperature for example. The non-uniform structure of semicoherent bcc/bcc U-Zr interfaces is studied using molecular dynamics simulations. Misfit dislocation patterns and their characters as well as their associated elastic lattice distortions are investigated as a function of various interfacial misfit strains and surface orientations. Results from the atomistic model will be compared with classical elasticity theories to highlight their implications for the relief of coherency stresses at interfaces, and for their mechanical properties.

4:20 PM  Invited
The Atomic Level Structure and Chemistry of Interfaces Between Iron and Cementite: Christopher Weinberger1; Matthew Guziewski1; Shawn Coleman2; 1Drexel University; 2Army Research Laboratory
    While the behavior of steel has been studied extensively for decades, there are still open questions regarding the microstructures it forms especially at the interfacial level. In this talk, we examine the validity of atomistics in gaining further insight into the structure of pearlite with particular emphasis on the Bagarystkii Orientation. The structure of the interface is shown to always be comprised of a set of perpendicular dislocations. However, the amount of spreading of the interfacial dislocations depends on which of the cementite planes form the interface, demonstrating the importance of chemistry. This, in turn, controls the interfacial energy, which will dictate the actual interfacial structure. A continuum model compares well both energetically and structurally with the atomic level models but fails to discern chemistry (and hence local structural effects) highlighting the need for atomic level descriptions. Coupling between this atomic structure and deformation will also be discussed.

4:40 PM  
Influence of Grain Boundary Transport on Transient Oxidation: Pralav Shetty1; Jessica Krogstad1; 1University of Illinois, Urbana-Champaign
    Despite being only a small fraction of the overall lifetime of a given component, the transient stages of oxidation prior to the formation of a continuous scale, can dramatically influence the type, adherence and the longer-term growth kinetics of the developing scale. Here we explore the earliest stages of oxidation, by focusing on mass transport both to and along grain boundaries in nanocrystalline alloys. Physical vapor deposition methods have been used to fabricate nanocrystalline Ni-based alloy thin films. Free-standing films were subjected to conventional weight-gain experiments using thermogravimetric analysis and then correlated with in situ (environmental) transmission electron microscopy experiments. We show that mass transport along the high density of grain boundaries towards the oxidizing surface can be tuned by slightly modifying the grain boundary chemistry. This is similar to the thermodynamic approach of nanocrystalline grain boundary stabilization for improved mechanical performance.

5:00 PM  
Strong Nonlinear Increase in the Yield Strength Due to Solute Segregation at Grain Boundaries in FCC Nano-crystalline Metals: Valery Borovikov1; Mikhail Mendelev1; 1The Ames Laboratory
    We used Monte Carlo and molecular dynamics simulations to study the effect of Cu solute atoms segregated at grain boundaries (GB) in nano-crystalline Ag on dislocation nucleation under applied tensile stress. We observed strongly non-linear increase in the yield stress with increasing solute concentration. The detailed analysis of the simulation data revealed that in the pure system under applied stress the dislocations nucleate from both the E units at the GBs and the triple junctions. Addition of solutes halts the dislocation nucleation and emission from the E units at the GBs, but the triple junctions are still able to emit the dislocations. Once all favorable segregation sites at the E units at the GBs are filled, the solutes segregate at the triple junctions and the yield stress increases dramatically. Yet, at some solute concentration the yield stress reaches a maximum and then decreases with further increase of the solute concentration.

5:20 PM  Invited
Atomistic Study of Fundamental Character and Motion of Dislocations in Intermetallic Al2Cu: Jian Wang1; Amit Misra1; 1University of Nebraska-Lincoln
    Al-intermetallic eutectic composites are typical structural materials because of their lightweight and high strength comparable to steel. Al-Cu alloys with a high volume fraction of nanoscale intermetallic precipitates (Al2Cu) exhibit enhanced ductility and strength at room temperature while improved strength at elevated temperatures. Understanding fundamental character and motion of dislocations in Al2Cu is essential for advancing microstructural design of Al-intermetallic eutectic composites. Using atomistic simulations, we studied seven slip systems in Al2Cu. Three edge dislocations with Burgers vector <001> on glide planes (110), (010), and (310), show an extended core, and glide at room temperature. Other four edge dislocations and three screw dislocations with Burgers vectors <001>, <110>, and 1/2<111> show a condensed core, and don’t glide at room temperature. Furthermore, Interaction of dislocation dipole results the climb of the extended-core dislocation at moderate temperatures. Interface structures of Al-Al2Cu and their roles in mechanical deformation are studied and discussed.