Deformation and Transitions at Grain Boundaries VII: Mesoscale Characterization and Simulation of Polycrystal Deformation
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
Thursday 8:30 AM
February 27, 2020
Room: 5B
Location: San Diego Convention Ctr
Session Chair: Zachary Cordero, Rice University; Thomas Bieler, Michigan State University
8:30 AM
Bridging the Gap Between Grain Boundary Experiments and Simulations via Engineered Oligocrystals: Zachary Cordero1; Logan Ware1; 1Rice University
Simulations of grain boundary phenomena often consider highly idealized grain boundaries or grain boundary networks. By contrast, experimental investigations on grain boundaries typically use polycrystalline specimens with poorly controlled structures and textures. This disconnect makes it difficult to directly compare experiments and simulations to validate grain boundary structure-property relations. To overcome this challenge, we have developed a directional solidification technique for growing oligocrystals with precisely controlled 3D grain boundary networks. In our approach we tailor the texture by using multiple seed crystals and control the position and orientation of each individual grain boundary by manipulating heat transfer effects as well as the thermodynamic forces that act on the boundary during crystal growth. This talk will summarize this processing strategy, its underlying physical principles, and its application to a novel class of bi- and tricrystal geometries for probing unanswered questions related to shear-coupled grain boundary motion.
8:50 AM
Characterization of Strain at Twin Boundaries in Ni-base Superalloys via Dark Field X-ray Microscopy: Sven Gustafson1; Wolfgang Ludwig2; Paul Shade3; Diwakar Naragani1; Darren Pagan4; Michael Sangid1; 1Purdue University; 2European Synchrotron Radiation Facility; 3Air Force Research Laboratory; 4Cornell High Energy Synchrotron Source
Polycrystalline materials, specifically Ni-base superalloys, see common use in high temperature applications such as the turbine of jet engines. During cyclic loading, localization of intragranular strain due to crystallographic slip acts as a catalyst for crack initiation, often at coherent twin boundaries. In this work, a high-resolution characterization of a region near a twin boundary is presented of a polycrystalline Ni-based superalloy (LSHR) subjected to fatigue loading. Dark-field x-ray microcopy is used to directly measure the intragranular misorientation and elastic strain within a grain of interest with 200nm spatial resolution. The extreme strain gradients seen within the material validate those presented in a EVP-FFT crystal plasticity model and indicate the presence of high residual stress gradients approaching a coherent twin boundary. The present work shows that sub-surface, high-resolution, 3D data is necessary to help elucidate the deformation near grain boundaries and suggests the importance of strain gradients in deformation models.
9:10 AM
Slip bands in Ni-base Superalloys: A Crystal Plasticity Study Informed by Digital Image Correlation: Marat Latypov1; Jean-Charles Stinville1; Jonathan Hestroffer1; Marie-Agathe Charpagne1; Tresa Pollock1; Irene Beyerlein1; 1University of California, Santa Barbara
Recent advances in characterization techniques, such as high-resolution digital image correlation (DIC), provided valuable insight into strain localization and formation of slip bands in polycrystalline Ni-base superalloys. Experiments show that intense slip bands often form at coherent twin boundaries at the onset of deformation. These slip bands undergo complex interaction with the polycrystalline microstructure and its non-uniform deformation imposed by macroscopic loading. In this work, we investigate these interactions by crystal plasticity finite element (CPFE) methods. Towards this end, we develop a new CPFE framework for explicit modeling of slip bands directly informed by DIC measurements. Following the presentation of the new framework, we will discuss key findings concerning the micromechanics behind slip transmission and stress concentrations near intense slip bands observed experimentally.
9:30 AM
Relationship Between Microstructure and Mechanical Properties of Super Duplex Stainless Steel: Mohammed Ali Lakhdari1; Hugo Van-landeghem2; Florent Krajcarz3; Guilhem Martin2; Laurent Delanny4; Jean-Denis Mithieux3; Muriel Veron2; 1Aperam / SIMaP; 2SIMaP; 3Aperam; 4Université catholique de louvain
The high mechanical strength of UNS S32750-type superduplex stainless steel is controlled by the characteristics of its fine-grained dual-phase austenite-ferrite microstructure, obtained through dedicated thermomechanical treatments. In order to achieve even higher strength, it appears necessary to identify the microstructural parameters, e.g. phases and grain morphology, crystallographic texture and phase fractions, governing the elasto-plastic behavior. To this end, model microstructures were generated to isolate the effect of those parameters from each other. Interrupted tensile tests followed by microscopic characterization (EBSD mapping and TEM observation) were carried out to relate the mechanical behavior to the evolution of texture and dislocations for the different materials. SEM in-situ tensile tests were conducted to determine the local strain distribution within the phases. These results were used to validate and optimize a crystal plasticity finite element model that describes the mechanical response of the material as a function of crystallographic texture.
9:50 AM
Strain Localization and Martensitic Transformations at Shear Bands in a Low Stacking Fault Energy Austenitic Stainless Steel: Douglas Medlin1; J. Sabisch1; C. San Marchi1; J. Ronevich1; 1Sandia National Laboratories
Deformation bands in austenitic stainless steels are often dominated by planar dislocation slip, but can also be tied to shear-coupled crystallographic transformations including twinning and the formation of ε-martensite. The interplay between strain and atomic shuffling in these bands can also drive further processes, such as the nucleation and growth of the α'-martensite phase at deformation band intersections. Here, we discuss electron microscopic observations of such bands and their relationship to grain boundaries and dislocation cell-walls in a low SFE austenitic stainless steel (304L), with and without hydrogen charging. Diffraction contrast STEM, nano-beam diffraction, and atomic-resolution observations provide fundamental insight concerning the elementary processes governing the nanoscale evolution of these structures.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the USDOE’s NNSA under contract DE-NA-0003525.
10:10 AM Break
10:30 AM
Influence of Crystal Orientation and Berkovich Tip Rotation on the Mechanical Characterization of Grain Boundaries in Molybdenum: Verena Maier-Kiener1; Severin Jakob1; Helmut Clemens1; Reinhard Pippan2; 1Montanuniversität Leoben; 2Austrian Academy of Sciences
Interfaces like grain boundaries play a crucial role for the performance of modern metallic materials. For example, molybdenum is used for applications in harsh environments because of its outstanding mechanical and thermal properties. However, depending on the processing state, fracture occurs to a certain extent along the grain boundaries. A method for the mechanical characterization of individual grain boundaries is therefore desired.A promising technique for this task is nanoindentation since it can achieve high spatial resolution of mechanical data without cumbersome sample preparation, thus allowing high throughput testing. It turns out, that the rotation of a pyramidal indenter can bias the observed hardness increase near an interface. The distinct influence of crystal orientation in combination with the indenter geometry will be discussed in detail.
10:50 AM
A Crystal-plasticity Modeling Framework to Study Effect of Grain Size on Mechanical Response of Open-cell Aluminum Foam: Dongfang Zhao1; Kristoffer Matheson1; Brian Phung1; Michael Czabaj1; Ashley Spear1; 1University of Utah
Open-cell metallic foams are hierarchical structural materials that have applications as light-weight impact absorbers, noise insulators, and heat sinks, to name a few. We investigate the dependence of macro-scale mechanical response on grain structure of open-cell aluminum foam using a high-fidelity numerical framework with crystal-plasticity finite-element (CPFEM) modeling. The CPFEM framework is able to capture deformation mechanisms across multiple length scales of the foam by accounting for interactions among discrete grains of different crystallographic orientations. Grain-boundary strengthening and free-surface softening mechanisms have been implemented into the CPFEM framework to account for, respectively, the Hall-Petch effect and the effect of unconstrained slip-based deformation associated with high specific surface area inherent to open-cell foams. Eight microstructural instantiations (overlaid on a foam volume derived from X-ray tomography) are simulated to investigate the grain-size effect on local and global mechanical properties. The new insight and modeling framework enable grain-scale-based design of open-cell metallic foams.
11:10 AM
A Multiphysics, Mesoscale Framework to Predict the Creep-fatigue Life of Engineering Polycrystalline Alloys: Andrea Rovinelli1; Mark Messner1; David Parks2; T.L. Sham1; 1Argonne National Laboratory; 2Massachusetts Institute of Technology
At high temperatures, the life of structural components is closely related to grain boundary (GB) network attributes. During fabrication, precipitates segregate at high energy GBs because of the energetically favorable configuration, becoming preferred sites for void nucleation. Crystallographic defects migrate from the grain bulk and remain trapped at GBs enhancing the void growth process. The coalescence of voids eventually results in intragranular fracture of the component. The time required to transition from void growth to intragranular fracture is closely related to the average GB character.To predict the engineering properties of a polycrystalline alloys subject to creep loads we developed a microstructure sensitive mesoscale framework. The framework combines: a multiphysics crystal plasticity model to capture strain heterogeneity and defects diffusion, and (ii) a cohesive GB model sensitive to the local GB character. Computational results show that the creep-fatigue life can be improved by increasing the amount of low energy GBs.
11:30 AM
Characterization and Modeling of the Microstructure-scale Strain Distributions in an Aluminum Alloy Under Multiple Strain Paths: Baran Guler1; Ulke Simsek1; Tuncay Yalcinkaya1; Mert Efe1; 1Middle East Technical University
Aluminum alloys exhibit localized deformation at the microstructure scale, which may have negative implications on the macroscale mechanical and forming behavior. In this work, micro- and meso-scale deformation behavior of a 6061-T6 aluminum alloy is investigated under large strains (>0.1) and various strain paths (uniaxial vs biaxial). While the strain localizes mostly to the grain boundaries under uniaxial tension, it is possible to observe localizations to both grain interiors and boundaries under biaxial tension. Grain size and orientation have considerable effects on the strain distribution, yet the effect of precipitates is minimal. When the strain maps at large field of views (100+ grains) are compared with the classical CPFEM simulations, there is little success in capturing the localizations. This is also a common problem identified in the literature and a non-local, strain-gradient CPFEM approach is utilized in this study for a far better match between the experiments and simulations.
11:50 AM
Anisotropy Grading Effects on Strength and Ductility: S. Mohadeseh Taheri-Mousavi1; Dingshun Yan2; C. Cem Tasan1; 1Massachusetts Institute of Technology; 2Chinese Academy of Sciences
Engineering lighter vehicles, higher buildings, and larger planes create an everlasting need for superior metallic materials which exhibit simultaneously high strength and ductility. Employing conventional bulk material processing methods, we demonstrate a microstructure design strategy to improve strength-ductility combinations. This approach includes coupling a crystallographic texture gradient to a weak grain size gradient (i.e. > 200 times weaker than that of conventional grain size graded materials). Proof-of-principle tests led a 1 GPa automotive sheet steel to increase its tensile ductility by 50% and its strength by 12%. Our molecular dynamics and crystal plasticity finite element simulations reveal that the main reason for the improvement in mechanical properties is a reduction in the stress triaxiality. Therefore, by redistribution of the internal stress due to gradient transverse deformation, the void growth on grain boundaries is delayed. The concept can potentially be readily applied to different alloys or other thermo-mechanical treatments.