Deformation and Transitions at Grain Boundaries VII: Grain Boundary-Dislocation Interactions
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
Wednesday 8:30 AM
February 26, 2020
Room: 5B
Location: San Diego Convention Ctr
Session Chair: Samuel Hemery, Ensma - Institute Pprime ; Samantha Daly, University of California - Santa Barbara
8:30 AM Invited
Atomistic Simulations of Grain Boundary-dislocation Interactions in Mg and Mg Alloys: Liang Qi1; Chaoming Yang1; Mingfei Zhang1; Yong-Jie Hu1; 1University of Michigan
It is difficult to discover the minimum energy structures of grain boundaries (GBs) at the atomistic scale because of many degrees of freedoms (DOFs). Such problems often occur for GBs of metals/alloys with HCP lattice, which has two atoms in one primitive cell. To solve these problems, we have developed an efficient genetic algorithm for predicting the minimum energy structures of metallic grain boundaries. This algorithm can automatically consider the addition/removing of atoms in/near GBs and the translational shift of grains to thoroughly search the microscopic and atomistic scale DOFs. We have applied this algorithm to efficiently construct different stable GBs for Mg and Mg binary alloys, such as faceted GBs and GBs with ordered solute segregations. Based on these GB structures, the dislocation-grain boundary interactions in both pure Mg and Mg alloy systems are studied to investigate the alloying effects on dislocation emission and transmission through GBs.
8:50 AM
Inhibiting Twin Transfer in Magnesium Alloys with Grain Boundary Particles: Benjamin Anthony1; Brandon Leu2; Wai Tse3; Zhenhuan Wang4; Irene Beyerlein2; Victoria Miller1; 1University of Florida; 2University of California Santa Barbara; 3University of New South Wales Sydney; 4North Carolina State University
Twinning is a critical deformation mechanism in magnesium alloys due to its ability to accommodate bulk strain at room temperature. However, instances of twin transfer – twin nucleation across grain boundaries due to stresses imposed by the twin tip – can lead to twin chains forming throughout the microstructure, contributing to texture formation and serving as a preferential failure pathway even at relatively low strains. Grain boundary particles were considered for their role in preventing stress field formation in neighboring grains, thereby blocking twin transfer. Compression testing followed by electron backscatter diffraction imaging was used to examine the changes in twinning behavior with varying amounts of grain boundary particles in both rare-earth-containing and rare-earth-free magnesium alloys. Additionally, computational experiments were performed using a Crystal Plasticity Fast Fourier Transform (CP-FFT) model to determine how particle morphology and neighbor grain misorientation influence the ability of a hard particle to prevent twin transfer.
9:10 AM
Manipulating Twin Morphology in Mg Alloys by Varying Solute Concentration: Yang Hu1; Vladyslav Turlo1; Irene Beyerlein2; Subhash Mahajan3; Enrique Lavernia1; Julie Schoenung1; Timothy Rupert1; 1University of California, Irvine; 2University of California, Santa Barbara; 3University of California, Davis
Twinning is an important deformation mechanism in Mg alloys that often determines their strength and ductility, yet it still remains unclear how solutes interact with twin boundaries and affect twin growth. In this talk, we discuss how twin evolution can be manipulated in Mg and Mg-Al alloys by varying solute composition. Using molecular dynamics, twin embryo growth in Mg-Al alloys with Al concentration varying from 0 to 10 at.% Al, is first explored. We show that solutes are able to alter the preferred twinning direction, while embryo twin length vs. thickness exhibits a power (log-log) dependence for all alloys. Using a newly developed phenomenological model, which emphasizes disconnection propagation on twin boundaries, we explain the log-log dependence of twin size observed in our atomistic simulations. Our work sheds light on the emerging technique of improving Mg alloy properties via construction of twin mesh networks.
9:30 AM
Estimation of Misfit Dislocation Density in Hexagonal Titanium Using Microbeam X-Ray Diffraction and the Frank Bilby Equation: Harsha Phukan1; Thomas Bieler1; Chen Zhang2; Ruqing Xu3; Philip Eisenlohr1; Martin Crimp1; Carl Boehlert1; 1Michigan State University; 2Carnegie Mellon University; 3Argonne National Laboratory
The present study focuses on determination of the geometrically necessary dislocation density in deformed commercial purity Titanium. Data collected from an in-situ differential aperture X-ray microscopy (DAXM) study of an in-situ four-point bending experiment at a surface strain of about 3.5% strain is used for this purpose. The misfit dislocation density estimation is carried out on a set of finer resolution line scans in two mutually perpendicular directions. Diffraction streak analysis is used to identify the misfit plane normal between adjacent voxels and the misfit dislocation density is calculated using the Frank Bilby equation. In particular, the study highlights the gradient of misfit dislocation density near the interface of two grains that have a “hard” and “soft” orientation with respect to the loading direction.
9:50 AM Invited
Interactions Between Slip Bands and Grain Boundaries in Ti-6Al-4V: Samuel Hemery1; Christophe Tromas2; Patrick Villechaise1; 1Institut Pprime - ISAE-ENSMA; 2Institut Pprime - Uinversité de Poitiers
Prior studies highlighted that interactions between slip bands and grain boundaries play a key role in the early damage stages in titanium alloys under a wide range of loading conditions including monotonic and cyclic tests. The understanding of such processes is thus a major concern for improving the microstructures and properties of these alloys. Slip activity in α grains of a deformed Ti-6Al-4V specimen with a bi-modal microstructure was analyzed. Operating slip systems were identified based on a slip traces analysis carried out using electron back-scattered diffraction and atomic force microscopy. In particular, the processes associated with interactions between slip bands and grain boundaries were investigated. The 3D geometry of the boundary, which was revealed using focused ion beam milling, was also considered. A quantitative analysis is presented based on slip step height measurement.
10:10 AM Break
10:30 AM Invited
Grain Boundary Sliding and Slip Transmission in High Purity Aluminum: Marissa Linne1; Thomas Bieler2; Samantha Daly3; 1University of Michigan; 2Michigan State University; 3University of California, Santa Barbara
This work examines the relationship between grain boundary sliding (GBS) and slip transmission at grain boundaries (GBs) by the experimental characterization of full-field strain and microstructural information in a highly modellable system of high-purity (99.99%) nominally columnar aluminum subjected to uniaxial tension at 190 °C. It was determined that GBS magnitude profiles can have large gradients along a single GB and vary significantly between GBs. Using a geometric compatibility factor (m′) to quantify favorability of slip transmission, a correlation between the average GBS magnitude and direct transmission was observed for moderately well-aligned slip systems. Cases will be presented that highlight important microstructural factors in predicting mechanism interaction, including the finding that direct transmission and GBS were anti-compatible and facilitated by opposing boundary types (low misorientation and high energy grain boundaries respectively), and that increased GBS activity correlated with decreased indirect transmission behavior.
10:50 AM Invited
On the Effect of Slip Transfer and Grain Boundary Sliding on the Deformation Mechanisms of FCC Polycrystals: Eugenia Nieto1; Sarra Haouala2; Alberto Orozco-Caballero3; Thomas Bieler4; Javier Llorca1; 1IMDEA Materials Institute & Technical University of Madrid; 2IMDEA Materials Institute; 3Technical University of Madrid; 4Michigan State University
A strategy based on experiments and simulations is presented to ascertain the influence of slip transfer and grain boundary sliding on the deformation of FCC polycrystals. From the experimental viewpoint, thin foils of Al and Ni oligocrystals were prepared and analysed by EBSD to determine the grain orientation and the character of the grain boundaries. They were tested in tension and the occurrence (or not) of slip transfer across the different grain boundaries and gran boundary sliding was ascertained from the analysis of the slip traces in the SEM and HR-DIC. In parallel, the mechanical behaviour of the oligocrystals was simulated with a dislocation-based crystal plasticity model that can take into account slip transfer/blocking and grain boundary sliding.The analysis of the experimental results and of the numerical simulations provided a deeper understanding of the role of the grain boundaries on the deformation mechanisms of FCC polycrystals.
11:10 AM
Fatigue-induced Slip from Type II Twin Boundary Motion of Shape Memory Alloys: Ahmedsameerkhan Mohammed1; Huseyin Sehitoglu1; 1University of Illinois Urbana-Champaign
Shape Memory Alloys (SMAs) are technologically important functional materials with widening application domains from biomedical devices to soft-robotic actuators and space exploration rovers. The performance-limiting phenomenon of functional fatigue has mandated an understanding of fatigue-induced slip mechanisms. This study proposes the mechanism as a consequence of inhibited grain boundary motion during martensitic phase transformation in SMAs. The grain boundary is a Type II Twin Boundary (TB), common in these alloy systems. NiTi, the most successful SMA, is analyzed from an atomistic and topological modeling standpoint. The yet unknown interface structures for the TB and also the transformation habit plane are proposed and an emissary dislocation reaction is proposed in two stages. The first stage proposes a fault partial emission on the TB and the second stage proposes the interaction of the fault partial with the habit plane explaining the emission of a perfect slip dislocation into the austenite phase.
11:30 AM
Quantifying the Plastic Deformation Behavior of Grain Boundaries in Additive Manufactured Ta: Nan Li1; jordan Weaver2; Yuchi Cui3; David Jones1; Nathan Mara4; Saryu Fensin1; Curt Bronkhorst5; Amit Misra3; Rusty Gray1; 1Los Alamos National Laboratory; 2National Institute of Standards and Technology; 3University of Michigan, Ann Arbor; 4University of Minnesota-Twin Cities; 5University of Wisconsin - Madison
The plastic deformation behavior of grain boundaries in additive manufactured Ta has been explored through micropillar compression and in situ TEM indentation experiments. In the micropillar compression tests, three high angle grain boundaries are chosen with varying crystal orientations. The main phenomenon of interest was slip transmission or strain transfer in the bi-crystals which was considered to occur when slip traces aligned across the grain boundary. These observations were compared against two slip transmission factors, m^'=cos(ψ)cos(κ)and A=LRB=cos(θ)cos(κ), where 𝜓, 𝜃 𝑎𝑛𝑑 𝜅 are the angles between the slip vectors, slip plane normal, and the intersection of the slip planes with the grain boundary from the slip systems on either side of the grain boundary. Slip transmission occurred for 𝑚′ ≥ 0.85 and did not occur for 𝑚′ ≤ 0.46. In addition, in situ indentation has been performed in the vicinity of grain boundary to probe correlated interaction behavior with dislocations.
11:50 AM
Investigation of Dislocation Interactions in a Bicrystalline Micropillar Through an Atomistically-informed Discrete Dislocation Dynamics Model: Nicole Aragon1; Jamie Gravell1; Ill Ryu1; 1University of Texas at Dallas
Nanostructured metals have attracted attention due to their appealing mechanical properties of good ductility and high strength. To understand the underlying mechanisms that control the mechanical properties of nanostructured metals, an insight into the role of the grain boundary in dislocation-driven plastic deformation is vital. In previous studies, the grain boundary has been observed as a dislocation source, sink or having no effect, which in turn, gives rise to different mechanical responses upon various loading conditions. With this motivation, our study characterizes dislocation interactions (absorption, transmission and nucleation) with the grain boundary via atomistic modeling, based on which we also developed a discrete dislocation dynamics model. With the atomistically-informed dislocation dynamics model, we explore the effect of varying misorientation angle for pure twist and pure tilt grain boundaries on plastic deformation of nanostructures, which could provide a better understanding of dislocation driven plasticity for polycrystalline metals at small scale.