Deformation and Transitions at Grain Boundaries VII: Grain Boundary Evolution
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Computational Materials Science and Engineering Committee
Program Organizers: Saryu Fensin, Los Alamos National Laboratory; Thomas Bieler, Michigan State University; Shen Dillon, University of California, Irvine; Douglas Spearot, University of Florida; Jian Luo, University of California, San Diego; Jennifer Carter, Case Western Reserve University
Tuesday 2:00 PM
February 25, 2020
Room: 5B
Location: San Diego Convention Ctr
Session Chair: Mitra Taheri, Johns Hopkins University; Douglas Spearot, University of Florida
2:00 PM Invited
Phase Transitions in Grain Boundary Dynamics: Kongtao Chen1; Jian Han1; David Srolovitz2; 1University of Pennsylvania; 2City University of Hong Kong
Grain boundary (GB) migration, sliding, shear coupling, roughening,... are controlled by the formation and motion of disconnections - line defects with dislocation and step character. In many situations, disconnection dynamics are dominated by the step character. However, when the dislocation character is significant (as in all GB shear coupling scenarios), long-range elastic interactions become important.They are particularly significant at low temperature. However, as temperature increases, the long range interactions between disconnections are increasingly screened by other disconnections. There is a critical temperature where this screening is dominant and the long range interactions again becomes unimportant. This leads to a transition in many GB dynamical parameters, such as GB mobility. This transition is a manifestation of a Kosterlitz-Thouless 2D phase transition.
2:20 PM Invited
Grain Boundary Spinodals: The Role of the Interface Stiffness in Grain Boundary Dynamical Processes: Fadi Abdeljawad1; Robert Moore1; Timothy Beecroft1; 1Clemson University
Many materials phenomena are classified as moving boundary problems. Of particular interest are ones involving the motion of grain boundaries (GBs) when subjected to external fields. When solving such problems at the mesoscale, sharp interface equations are derived to describe GB dynamics, in which the interface properties serve as key input parameters. Through theoretical analysis and atomistic simulations, we show that when considering the GB plane normal degrees of freedom, the interface stiffness plays a paramount role in a wide range of processes, including dislocation nucleation, GB migration, and re-construction processes. It is shown for several GBs that the interface stiffness is much larger in magnitude and more anisotropic than the energy itself. On the whole, our analysis provides future avenues to explore the role of GB plane normal in GB dynamical processes.
2:40 PM
A New Approach to Modeling Grain Boundary Motion with Strongly Anisotropic Boundary Energy: Brandon Runnels1; Vinamra Agrawal2; 1University of Colorado Colorado Springs; 2Auburn University
Microstructure evolution is effectively modeled using the phase field method, but grain boundary (GB) energy anisotropy and orientation dependence induce complexity in constructing the Allen Cahn equation. Furthermore, determining an accurate estimate of free energy for GBs with arbitrary orientation is challenging due to the large space of GB configurations and relatively sparse knowledge of energy data. As such, even rudimentary simulations with orientation dependence are restricted to certain cases with well-known boundary energy. A method is developed for constructing the Allen-Cahn equation for GB migration including an orientation-dependent, nonconvex, anisotropic boundary energy. To incorporate realistic boundary behavior, the lattice-matching model is used to calculate boundary energy for arbitrary orientations, on-the-fly. It is shown that the phase field model accurately captures minimum energy morphology for multiple energy functionals, lengthscales are induced and controlled by the second order term, and experimentally observed microstructure is reproduced.
3:00 PM
An Atomistic Survey of Grain Boundary Migration Mechanisms in BCC Fe: Ian Chesser1; Sutach Ratanaphan2; Brandon Runnels3; Elizabeth Holm1; 1Carnegie Mellon University; 2King Mongkut's University of Technology Thonburi; 3University of Colorado Colorado Springs
In this work, we examine the migration mechanisms of 408 BCC Fe bicrystals driven by a shear stress and energy jump driving force with variable boundary conditions. A zoo of migration mechanisms including sliding, shear coupled motion, motion coupled to vacancy ejection, boundary splitting, and zig zag motion are analyzed. We seek to unify these phenomena in a continuum model for grain boundary yield and mobility inspired by models for slip selection in crystal plasticity. Yield statistics for BCC boundaries are compared to yield statistics from the canonical Olmsted FCC Ni dataset.
3:20 PM
Interrelationship Between How Grain Boundary Solute Segregation Influence Grain Coarsening, Initiation of Phase Transformations, and Impact Deformation Mechanisms of Metallic Alloys: Arun Devaraj1; Libor Kovarik1; Elizabeth Kautz1; Bharat Gwalani1; Aashish Rohatgi1; Wenbo Wang2; Jason Trelewicz2; Vineet Joshi1; Curt Lavender1; 1Pacific Northwest National Laboratory; 2Stony Brook University
The fundamental mechanistic influence of solute segregation on the mobility of grain boundaries during thermal annealing, as well as during deformation, is a topic of great interest both in fundamental and applied physical metallurgy domains. Another closely related topic is how solute segregation and precipitation of secondary phases at grain boundaries can be manipulated to control the extent and kinetics of phase transformations initiating at grain boundaries. The main aim of this talk is to highlight the interrelationship between these seemingly different topics. We will present how the relative influence of thermodynamic stabilization of grain boundaries by solute segregation or kinetic pinning by precipitation, would influence several phenomena in various metallic systems, including: thermal coarsening of light weight nanocrystalline Al-Mg alloys; modification of phase transformation kinetics of grain boundary initiated discontinuous precipitation in UMo alloys; and influences on the shear deformation mechanism of model metallic alloys (e.g. Al-Mg and Al-Si).
3:40 PM Break
4:00 PM Invited
Pinning of a Grain Boundary Migration by Coherent Second Phase Particles: Nan Wang1; Youhai Wen2; Long-Qing Chen3; 1Guangdong Technion-Israel Institute of Technology; 2NETL; 3Pennsylvania State University
Pinning of grain boundary migration using second-phase particles is one of the most efficient ways to limit the grain growth of a polycrystalline grain structure. An interfacial-energy-based pinning theory proposed by Zener has long been used to explain the pinning mechanism of second phase particles on grain boundary migration. Coherent second-phase particles are often designed to strengthen alloys to block dislocation motion. However, they also interact with migrating grain boundaries by exerting pinning forces on them during their migration. Here we present a novel pinning mechanism originated from the lattice misfit strain between coherent second phase particles and matrix and validate it by performing phase-field-crystal simulations. It is found that, depending on the relative contribution of interfacial energy and elastic energy, coherent second particles exhibit two modes of pinning with the strongest pinning effect taking place at the crossover region of the two pinning modes.
4:20 PM Invited
Linking Atomic and Mesoscale Descriptions of Grain Boundaries for Insight into Metastable Structures: James Nathaniel1; Cassandra Pate1; Larissa Woryk2; Jaime Marian3; Blas Uberuaga4; David Srolovitz2; Mitra Taheri1; 1Johns Hopkins University; 2University of Pennsylvania; 3University of California, Los Angeles; 4Los Alamos National Laboratory
Recent simulations that classify grain boundaries (GBs) according to microstates, or phases, present an opportunity to sharpen our understanding of radiation damage tolerance. GB stability may be defined as the ability of a GB to continue to absorb point defects without becoming saturated and without changing its macroscopic degrees of freedom (misorientation, inclination), or degrees of freedom. This talk shows that adding or removing atoms can change the GB microstate, and changes of GB microstate can alter the ability of GBs to influence radiation damage; we also explore radiation damage as a means of altering GB microstate. Through the use of in situ microscopy and quantitative dislocation density analysis coupled with both atomic and mesoscale simulations, a fundamental understanding of GB “states” evolve as a function of point defect absorption is presented. The results have profound implications in developing thermally stable, bulk nanocrystalline materials, and damage tolerant materials.
4:40 PM
Stress State Dependence of Basal-prismatic Facet Structures in Mg: Khanh Dang1; Shujuan Wang1; Mingyu Gong2; Carlos Tomé1; Rodney McCabe1; Jian Wang2; Laurent Capolungo1; 1Los Alamos National Laboratory; 2University of Nebraska-Lincoln
Recent efforts to characterize the 3D structure of the {101 ̅2}<1 ̅011> twins have shown that the twin domains is are surrounded by multiple facets such as: coherent twin boundary (CTB), basal-prismatic (BP), twist pyramidal-pyramidal, and twist prismatic-prismatic. Among them, the BP facet has gained significant attentions due to its low formation energy and its role in the twin nucleation and growth. In this work, we report the formation of long and straight semi-coherent BP facets from short coherent ones during relaxation using a combined technique of high-resolution transmission electron microscopy (HRTEM) and molecular dynamics (MD) simulations. Moreover, due to its low mobility, this semi-coherent facet prevents the twin from collapse in the absence of an applied shear stress. The transformation is also reversed once the twin is reloaded. Importantly, this transformation indicates that the final BP configuration observed in HRTEM is not necessary the one activated during twin growth.
5:00 PM
Structure and Kinetics of Three-dimensional Defects on the {10-12} Twin Boundary in Magnesium: Atomistic and Phase-field Simulations: Douglas Spearot1; Vincent Taupin2; Khanh Dang3; Laurent Capolungo3; 1University of Florida; 2University de Lorraine CNRS; 3Los Alamos National Laboratory
The objective of this work is to characterize the structure and kinetics of three-dimensional defects created via the interaction between a dislocation shear loop and the {10-12} twin boundary in Mg. Molecular statics calculations show that the three-dimensional defects are bounded by nonequilibrium facets along the prismatic/basal (PB) and twist pyramidal/pyramidal (PP1) interfaces. The kinetics of the twin domain facets at finite temperature are analyzed by both molecular dynamics and a new anisotropic phase-field model. The latter allows the deconvolution of the competing role of interface energy, mobility and internal stress state. Molecular dynamics simulations show that inclined facets control the annihilation process; this behavior is captured in the phase-field model using mobility for the CTB interfaces that is significantly lower than that of crater inclined facets. Further, MD simulation results are best matched via the introduction of facet orientation dependent excess energies.
5:20 PM Cancelled
Coarsening of Ferrite Lamellae Grains in Heavily Cold Drawn Pure Iron Wire: Hanchen Feng1; 1Southeast University
Microstructure and mechanical properties of heavily cold drawn industrial pure iron wires were investigated. Experimental results show that tensile strength of pure iron wires increased with the increasing of drawing strain. Tensile strength of cold-drawn pure iron wires increased from 350 MPa to 1812 MPa as the drawing strain (ε) increased to 10.35. And the equiaxed ferrite grains turned into fibrous grains. However, as the drawing strain was higher than 8.9, tensile strength of pure wires would not increase any more. Meanwhile, the coarsening of fibrous ferrite grains were observed in cold drawn wire (ε=8.9). Statistical results showed that the stability size of ferrite grain width was about 90 nm. Strengthening mechanism of heavily cold drawn industrial pure iron wire was discussed.Keywords：Cold-drawn; Mechanical properties; Coarsening; Transmission electron microscopy (TEM);