Deformation and Transitions at Interfaces : Deformation and Grain Growth in Polycrystalline 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

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

Session Chair: Khalid Hattar, Sandia National Laboratories

2:00 PM  Invited
The Zero-energy Grain Boundary and Consequences to Grain Growth: Ricardo Castro1; Nazia Nafsin1; 1University of California, Davis
    Nanocrystalline bulk materials (also called nanograined materials) are intrinsically unstable due to the excess energies coming from extensive grain boundary areas. Designed dopants prone to segregation to boundaries have been proposed to lower excess energies, increasing stability against coarsening and enabling the nanostructural features to survive high temperature processing and operational environments. It has been theoretically proposed that the grain boundary energy of a material can eventually zero as a function of dopant concentration, signifying negligible driving force for growth – an infinitely stable nanomaterial. In this work we use highly sensitive microcalorimetry to experimentally measure the absolute grain boundary energy of gadolinium doped nanocrystalline zirconia as a function of grain size and show that the energy can indeed reach a quasi-zero energy state (0.05 J.m-2) when a critical grain boundary dopant enrichment is achieved. This thermodynamic condition leads to unprecedented coarsening resistance.

2:20 PM  Invited
Exploring the Role of Texture, Grain Boundary Character, and Grooving on Grain Growth in Metallic Thin Films: Khalid Hattar1; Daniel Bufford1; Stephen Foiles1; Fadi Abdeljawad1; 1Sandia National Laboratories
    Gold thin films industrial relevant applications include the ubiquitous USB electrical connection. Despite this, the structural stability is still poorly understood, which is evident in the range of microstructural evolutions that have been experimentally observed. This work utilizes in-situ transmission electron microscopy (TEM) heating experiments, precession electron diffraction (PED), and atomic force microscopy (AFM) to characterize the initial and final structures, as well as to directly observe the evolution as a function of temperature. The information on local texture, grain boundary character, grain boundary grooving, and structural kinetics is directly incorporated into a phase field model to better understand the interplay of effects. This work was partially supported by the Division of Materials Science and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy. Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

2:40 PM  Invited
Electric Field Effects on Grain Boundary Formation and Grain Growth: Klaus van Benthem1; 1University of California, Davis
    The application of electric fields can enable the accelerated consolidation of materials during field assisted sintering. While such techniques are already employed for the synthesis of a variety of microstructures with unique macroscopic properties, a fundamental understanding of the scientific underpinnings for grain boundary formation and migration in the presence of electrostatic potentials is mostly absent from the literature. We have designed experiments to specifically de-couple the effects of heating and applied electrostatic fields during consolidation. In situ transmission electron microscopy studies were carried out with new sample holder designs to investigate densification and grain growth mechanisms in the absence and presence of electrical field. Quantitative experimental observations reveal lowering of activation energies for both densification and grain growth as a consequence of the applied electric field strength. In the specific case of flash sintering, microstructural characterization furthermore reveals that electrode effects can lead to non-homogeneous microstructure evolution during processing.

3:00 PM  Invited
Blocky Alpha Grain Growth in Zircalloy4: Vivian Tong1; T Ben Britton1; 1Department of Materials, Imperial College
    Grain boundaries are an important microstructural feature, often conferring improved mechanical properties. In materials engineered to have a fine microstructure and uniform texture (e.g. Zircaloy 4), the growth of very large grains (from ~10 μm to >1 mm) in thin parts is not desired. This process may occur due to abnormal grain growth mechanisms which initiate during annealing after low strain deformation. We use a combination of thermomechanical processing and characterisation (EBSD, DIC and HR-EBSD) to understand phenomena of blocky alpha grain growth and the role of different deformation mechanisms on the ultimate grain size and texture in Zr4. We observe striking textures and grain morphologies as a result of particular processing strategies due to deformation near particular grain boundaries. We correlate ultimate grain size, shape and texture with the sense and magnitude of strain applied, and relate these to mechanisms producing the final grain structure and texture.

3:20 PM  Invited
EBSD Observations of Deformation at Grain Boundaries: David Field1; 1Washington State University
    Dislocation motion is interrupted at grain boundaries by various mechanisms, including slip transfer and dislocation pileups, among others. Analysis of slip system activity at various grain boundaries by slip trace observation and EBSD analysis of crystallographic planes and directions allows for proper identification of active slip systems. Coordinated slip between grains, dislocation pileups, and grain boundary motion due to dislocation activity at grain boundaries are all observed and reported in this discussion.

3:40 PM Break

4:00 PM  
Transformation, Deformation and Special Grain Boundary Generation – Theoretical Analysis and Phase Field Simulations: Yipeng Gao1; Yunzhi Wang1; 1The Ohio State University
    Grain boundary plays an important role in determining a large number of material properties (e.g., strength, ductility, corrosion resistance, etc). In particular, a lot of attentions have been paid to special grain boundaries because of their special atomic structure and properties. By investigating the symmetry breaking during transformation and deformation, we propose a new method to produce special grain boundaries (GBs). The characteristic type of GBs generated is dictated by the broken symmetry during the process, which establishes a fundamental relationship between phase transformation and grain boundary engineering. Through a combination of phase transition graph analysis and phase field modeling, polycrystalline microstructures generated in Fe-based and Ti-based alloys and NiTi-bases shape memory alloys are investigated systematically and compared with experimental observations. The work provides new insight into engineering design of polycrystalline microstructure with mostly special grain boundaries through transformation and deformation.

4:20 PM  
Deformation at Grain Boundaries and Triple Junctions in Oligocrystalline Nickel: Ying Chen1; Mingjie Li1; 1Rensselaer Polytechnic Institute
    Deformation in polycrystalline materials is highly heterogeneous due to crystal orientation effects, the presence of interfaces such as grain boundaries and triple junctions, as well as three-dimensional grain constraint. To exclude the effect of three-dimensional grain constraint, we work with oligocrystalline metallic structures with a nearly columnar grain structure. Using nickel as a model material, we performed strain mapping using digital image correlation as well as crystallographic orientation mapping, and analyzed the correlation between interface character and local deformation. In this talk, we will present our preliminary experimental results, with a particular focus on deformation and strain localization at triple junctions.

4:40 PM  
Correlating Dislocation Configurations to Deformation Behavior in Cyclically Deformed Additive Manufactured IN718: Yung Suk Yoo1; Todd Book2; Michael Sangid2; Josh Kacher1; 1Georgia Tech; 2Purdue University
    Additive manufactured structural materials show great promise in rapid machining of complex parts, but their long-term deformation behavior remains poorly understood. This study focuses on correlating deformation analysis across length scales using digital image correlation (DIC), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) in IN718. DIC strain measurements coupled with EBSD-based orientation mapping were used to identify regions of interest such as high dislocation concentrations and deformation band interactions with grain boundaries in the cyclically deformed samples. Focused ion-beam (FIB) machining facilitated site-specific sample fabrication for in-depth dislocation characterization. Special emphasis was given to dislocation configurations found near twin boundaries as previous experiments have identified them as preferred fatigue crack nucleation sites. Discussion will focus on insights into the mechanics of crack formation as well as the effectiveness of coupling macroscale strain mapping techniques with local dislocation analysis to understand complex deformation processes.

5:00 PM  Invited
Effects of Materials and Processing Parameters on the Roughness of Recrystallization Boundaries: Dorte Jensen1; YuBin Zhang1; Jun Sun1; 1DTU Risų
    It has been shown that boundaries surrounding recrystallization grains often are rough with local protrusions and retrusions, i.e. with boundary segments which have migrated further or less than the nearby segments, respectively. The curvature forces are often large – of the same order of magnitude as the driving forces from the stored energy in the deformed matrix. In this work we present a statistical analysis of the grain boundary roughness as a function of material purity, plastic strain and boundary migration direction for a series of aluminium samples. It is shown that all 3 parameters affect the roughness and also that the roughness is scale dependent. Implications of the results on boundary migration are finally discussed.