Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales II: Session I
Program Organizers: Arul Kumar Mariyappan, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Levente Balogh, Queen's University; Josh Kacher, Georgia Institute of Technology; Caizhi Zhou, University of South Carolina; Lei Cao, University of Nevada
Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 35
Location: MS&T Virtual
Session Chair: Xuyang Zhou, Max-Planck-Institut fuer Eisenforschung GmbH; Ting Zhu, Georgia Institute of Technology
2:00 PM Invited
Bridging Computational Modeling and In Situ Experiment to Decipher Microscopic Deformation Mechanics: Ting Zhu1; 1Georgia Institute of Technology
With recent advances in computational modeling and in situ experiment technologies, there have been increased efforts to apply these approaches to understand microscopic mechanisms dictating deformation mechanics. In this talk, I will present our recent studies that combine in situ electron microscopy and diffraction experiments with crystal plasticity and atomistic simulations for gaining a deeper understanding of microscopic deformation mechanics. For example, we have combined in situ synchrotron X-ray diffraction experiments with crystal plasticity simulations to investigate microscale residual stresses in additively manufactured stainless steel. We have also combined in situ transmission electron microscopy experiments and atomistic simulations to study the effects of atomic structures and elemental distributions on achieving the unusual mechanical properties of high-entropy alloys. In addition, we have used this approach to reveal the grain boundary deformation atom by atom, step by step, thus uncovering the unexpected grain boundary sliding mechanisms in real time.
2:30 PM
Ultra-high strength and plasticity mediated by partial dislocations and defect networks: Ruizhe Su1; Dajla Neffati2; Yifan Zhang1; Yashashree Kulkarni2; Xinghang Zhang1; Zhongxia Shang1; 1Purdue University; 2University of Houston
Deformation mechanisms governing the strength of nanostructured metallic multilayers have been studied extensively for various applications. In general, size effect is the most effective way to tailor the mechanical strength of multilayers. Here we report that three Cu/Co multilayer systems with identical layer thickness but different types of layer interfaces exhibit drastically different mechanical behavior. In situ micropillar compression tests inside a scanning electron microscope show that coherent FCC (100) and (110) Cu/Co multilayer systems have low yield strength of about 600 MPa, and prominent shear instability. In contrast, the incoherent Cu/ HCP Co multilayers show much greater yield strength, exceeding 2.4 GPa, and significant plasticity manifested by a cap on the deformed pillar. Molecular dynamics simulations reveal an unexpected interplay between pre-existing twin boundaries in Cu, stacking faults in HCP Co, and incoherent layer interfaces, which leads to partial dislocation dominated high strength, and outstanding plasticity.
2:50 PM
Integrating Materials Models and Dynamical Electron Diffraction Simulations for Dislocation Analysis using STEM-Defect Contrast Imaging: Joseph Tessmer1; Mulaine Shih2; Yejun Gu3; Jafaar El-Awady3; Maryam Ghazisaeidi2; Marc De Graef1; 1Carnegie Mellon University; 2Ohio State University; 3Johns Hopkins University
The number and type of dislocations present in crystalline materials have a strong impact on material properties. Conventional Transmission Electron Microscopy (CTEM) has been used for decades to characterize dislocations in such materials. However, novel techniques such as Scanning Transmission Electron Microscopy Dislocation Contrast Imaging (STEM-DCI) can be used to characterize dislocations in a similar manner to CTEM, while suppressing undesirable image features, such as bend contours. Unlike dislocation imaging the CTEM modality, there is not yet a large body of work to which STEM-DCI images can be compared. This work aims to couple dynamical electron diffraction simulations with the output of multiple mechanical models, including Discrete Dislocation Dynamics and Molecular Dynamics. Such simulated images can be used to identify contrast features in experimentally obtained images, helping to verify the underlying features of the microstructure which produced those contrast features.
3:10 PM
Predicting the Stress Strain Behavior of Nickel Single Crystal Through an Integrated First-principles Calculation and Crystal Plasticity Finite Element Modeling Approach: Shipin Qin1; Shun-Li Shang1; John Shimanek1; Zi-Kui Liu1; Allison Beese1; 1Pennsylvania State University
In crystal plasticity models, the deformation mechanisms of single crystals are explicitly considered. However, the model parameters are typically determined through fitting of macroscopic experimental results and are rarely linked back to the underlying physical processes. In this presentation, the recent development of a multiscale approach that combines first-principles calculations and crystal plasticity finite element method (CPFEM) to predict the strain hardening behavior of pure Ni single crystal will be discussed. In the density functional theory (DFT)-based first principles calculations, the ideal shear stress of Ni single crystal at different pre-strain levels is predicted, which is then converted to the stress required for moving a dislocation, the Peierls stress, using a type of Peierls-Nabarro equation. The Peierls stress at different pre-strain levels provides the inputs for CPFEM model parameters, which are then adopted for predicting the engineering stress strain behavior of bulk Ni single crystal.
3:30 PM
ECCI Image Simulations for Arbitrary Defect Displacement Fields: Marcus Ochsendorf1; Joseph Tessmer1; Marc De Graef1; 1Carnegie Mellon University
Electron Channeling Contrast Imaging (ECCI) is an established method of imaging near-surface defects using Scanning Electron Microscopy (SEM). Traditionally, the types of ECCI defect images that can be readily simulated have been limited to those that have displacement fields that can be expressed analytically, which has somewhat limited the usefulness of the simulation approach. Molecular Dynamics (MD) and Discrete Dislocation Dynamics (DDD) simulations can be used to determine displacement fields of a variety of defect configurations. We will show that direct simulation of ECCI images based on MD or DDD displacement fields provides an opportunity for a quantitative one-to-one comparison between experiment and simulation, providing further insight on the mechanisms of defect behavior in a variety of material systems. ECCI simulation results will be provided for several defect types, including a dissociated dislocation in a medium entropy alloy, and an expanding dislocation loop wrapping around obstacles.