Probing Defect Properties and Behavior under Mechanical Deformation and Extreme Conditions: In Situ and Advanced Characterization of Defects
Sponsored by: TMS Nanomechanical Materials Behavior Committee, TMS Nuclear Materials Committee, TMS Mechanical Bahavior of Materials Committee
Program Organizers: Zhe Fan, Lamar University; Tianyi Chen, Oregon State University; Shijun Zhao, City University of Hong Kong; Mitra Taheri, Johns Hopkins University; Yury Osetskiy, Oak Ridge National Laboratory
Monday 2:00 PM
October 18, 2021
Room: B140/141
Location: Greater Columbus Convention Center
Session Chair: Xiaoqing Pan, University of California Irvine; Xinghang Zhang, Purdue University
2:00 PM Invited
Now On-Demand Only - Imaging Electronic Properties of Ferroelectric Interfaces and Domain Walls via 4D STEM: Christopher Addiego1; Huaixun Huyan1; Xiaoqing Pan1; 1University of California Irvine
Defects and other features that break translational symmetry, such as interfaces, grain boundaries, and domain walls, in crystalline materials are key factors in determining overall properties and can also lead to unique structures with deliberate engineering. Although advances in scanning transmission electron microscopy (STEM) have made determining the structure and composition of these features routine, determining the electronic properties remains challenging. Four-dimensional STEM (4D-STEM) offers one avenue for revealing the charge distribution of localized atomic-scale features without the computational cost associated with previous experimental methods or first-principles calculations. Here, we will discuss the applications of 4D STEM to studying the electric field and charge distribution in ferroelectric interfaces and domain walls. In BiFeO3, we find evidence of charge separation in both an interface with insulating SrTiO3 and at 109° domain walls through two different mechanisms. Applications to PbTiO3 interfaces and superlattices will also be discussed.
2:30 PM Invited
Ultra-high Strength and Plasticity Mediated by Partial Dislocations and Defect Networks: Ruizhe Su1; Dajla Neffati2; Yashashree Kulkarni2; Xinghang Zhang1; 1Purdue University; 2University of Houston
Prior studies show that size effect is the most effective way to tailor the mechanical strength of metallic 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 Cu/Co multilayer systems have low yield strength of about 600 MPa, and prominent shear instability. In contrast, the incoherent Cu/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. This study provides fresh insights for the design of strong, deformable nanocomposites by using a defect network.
3:00 PM
Probing Materials Properties across Scales with Scanning Diffraction in Transmission Electron Microscopy: Wenpei Gao1; 1North Carolina State University
Advances in instrumentation now enable the scanning diffraction to be taken in aberration-corrected scanning transmission electron microscopes (AC-STEM) at high special resolution. With new approaches in data analysis, this allows the imaging and quantification of various materials properties including symmetry, strain, electric and magnetic field. In this talk, we show our recent study on complex oxides: by coupling a pixelated detector with an AC-STEM, electric field and charge mapping can be obtained at atomic resolution; using atom-by-atom analysis, the electric dipole and its change across interfaces are revealed at the atomic scale; finally, by changing convergence angle, scanning diffraction can probe the sample properties across different scales, and reveal how phenomenon in long ranges emerges from the atomic scale. The application of scanning diffraction on other materials including metallic glass and high entropy oxide will also be discussed.
3:20 PM Break
3:40 PM
In-situ Study of Failure Defects in Cu/Nb Nanolaminates under Deformation: Yifan Zhang1; Nan Li1; Laurent Capolungo1; Matt Schneider1; Rodney McCabe1; 1Los Alamos National Laboratory
Mechanical properties of materials are strongly influenced by interfaces that are barriers and sources for defects. Nano-metallic laminates (NMLs), containing abundant and tailorable interfaces, are of great importance to understand defect-interface interactions. However, the anisotropic deformation modes and failure mechanisms of NMLs are less explored. In this work, deformation behaviors of Cu/Nb NMLs are investigated by using in situ compression both at micron scale (in situ SEM) and nano scale (in situ TEM) along layer-parallel and layer-normal directions. The nucleation and propagation of failure defects, such as kink band and shear band, during the deformation are recorded and analyzed with respect to stress-strain responses. Postmortem S/TEM, high-resolution TKD analyses reveal the failure-induced hierarchical microstructure evolution and defects distributions. Our study may advance the design of strong and failure resistant structure materials
4:00 PM Invited
In-situ Transmission Electron Microscopy of Intermittent Dislocation Activities and Deformation Mechanisms: Jian Min Zuo1; Haw-Wen Hsiao1; Yang Hu1; Qun Yang1; 1University of Illinois
We report on the observation of dislocation activities in compressed nanopillars using in-situ transmission electron microscopy (TEM) and the measurement of load- and displacement-time curves. Using this technique, the dislocation and grain boundary (GB) activities can be directly correlated with the mesoscopic mechanical response for a direct determination of deformation mechanisms. The results of such study for a range of materials will be presented, including nanocrystalline materials and high entropy alloys (HEAs). In the case of HEAs, we provide evidences of dislocation slip band formation and it is relationship to dislocation avalanches. In case of nanocrystalline materials, we follow the development of dislocations and dislocation motions in the selected nanograins. The observations reveal the mechanism of dislocation hardening, grain boundary deformation, and intermittent dislocation avalanches across multiple grains. Together, these results provide critical insights about nanoscale deformation mechanisms and their critical roles that contribute to the strength and plasticity.
4:30 PM
The Effects of Sample-preparation-induced Defects on the Mechanical Properties of Single Crystal Aluminum Nano-pillars: Yang Yang1; Sarah Wang2; Bin Xiang3; Sheng Yin2; Thomas Pekin2; Xiaoqing Li2; Ruopeng Zhang2; Kayla Yano4; David Hwang5; Mark Asta1; Costas Grigoropoulos2; Frances Allen1; Andrew Minor1; 1Lawrence Berkeley National Laboratory; 2UC Berkeley; 3USTC; 4PNNL; 5Stony Brook University
In situ TEM nano-pillar compression experiments have been extensively applied to decipher the mechanical behavior of materials at the nano-scale. However, the sample preparation process often inevitably introduces defects that may significantly impact the mechanical performance of samples with electron transparent dimensions. An understanding of the advantages and disadvantages of different sample fabrication methods is necessary to choose the most suitable method for a reliable experiment. Here, we systematically studied the effects of various focused-ion-beam (FIB) pillar fabrication parameters in a single crystal aluminum (Al) system with well-controlled crystal orientation. Also, we proposed a novel method to fabricate square-shaped pillars to minimize FIB artifacts such as tapering, high pillar base compliance, and preferential deformation at the pillar tip.
4:50 PM
In-situ Studies on Radiation Response of a Nanotwinned Steel: Zhongxia Shang1; Tongjun Niu1; Tianyi Sun1; Sichuang Xue1; Wei-Ying Chen2; Meimei Li2; Haiyan Wang1; Xinghang Zhang1; 1Purdue University; 2Argonne National Laboratory
Recent studies on nanotwinned pure metals, such as Cu and Ag, show that twin boundaries are appealing defect sinks during heavy ion irradiation as twin boundaries can transport and eliminate radiation-produced defects. However, the response of twin boundaries in nanotwinned structural steels under irradiation is rarely explored. Here, we investigate the microstructural evolution of a nanotwinned steel via in situ Kr++ irradiation at room temperature to ~ 4 dpa. The in situ study shows that nanotwins in steels can effectively suppress the formation of irradiation-induced dislocation loop rafts. Also the formation of loop rafts and Frank loops was found to depend prominently on twin spacing. The underlying mechanisms of enhanced radiation tolerance in nanotwinned steel are discussed. The present study provides a positive step towards the application of nanotwinned structural materials to nuclear industries.