Mechanical Behavior at the Nanoscale V: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Christopher Weinberger, Colorado State University; Megan Cordill, Erich Schmid Institute of Materials Science; Garritt Tucker, Colorado School of Mines; Wendy Gu, Stanford University; Scott Mao; Yu Zou, University of Toronto
Tuesday 5:30 PM
February 25, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr
Session Chair: Christopher Weinberger, Colorado State University
N-4 (Digital): Interface Diffusion and Thermodynamics Measured via High Temperature In-situ Mechanical Testing: Shen Dillon1; 1University of Illinois
This talk describes the use of a single grain boundary Coble creep type experiment performed via high temperature in situ TEM. These experiments can be used to measure grain boundary and surface energies and diffusivities. The method has been applied to ZrO2 from ≈1500 C to >2000 C. The results provide insights into transport mechanisms in nanoscale contacts.
N-5: A Novel Bimodal Microstructure for Improved Fatigue Resistance: Wenwu Xu1; Ken Ramirez1; Rachell Lee1; Sharier Hasan1; 1San Diego State University
The talk will present a new bimodal microstructure for improving metal fatigue using molecular dynamics (MD) modeling. In this bimodal microstructure, individual micrometer-sized grains are completely separated by a network of ultrafine nanocrystalline structure. MD simulations of low cycle fatigue deformation of the proposed bimodal microstructure suggest that most of the dislocations generated by the repeated plastic deformation are absorbed by the nanocrystalline network. No significant accumulation of dislocations is observed within the micrograins. This indicates that the formation of crack initiation is largely hindered in the bimodal microstructure. The underlying mechanism is probably related to the intrinsic characteristic of nanograin boundaries. The excess volume (or the width) of nanograin boundaries in the nanocrystalline network changes reversely during the repeated compression and tension, impacting the dislocation behavior within micrograins. This work suggests a potential path to achieve high fatigue resistance in metals as compared with their microcrystalline counterparts.
N-6: Atomistic Modeling of Fundamental Deformation Mechanisms in MAX Phases: Gabriel Plummer1; Garritt Tucker1; 1Colorado School of Mines
MAX phases are a large family of layered, ternary metal carbides and nitrides, which possess a unique combination of metallic and ceramic properties. While MAX phases have been recognized as remarkable materials and are utilized in a wide variety of applications, an understanding of their fundamental deformation mechanisms is still lacking. Atomistic modeling studies would contribute greatly to resolving this outstanding issue, but presently no appropriate interatomic potentials exist. Herein, utilizing a newly developed bond order potential for the Ti3AlC2 and Ti3SiC2 MAX phases, the mechanisms of MAX phase deformation are probed, with an emphasis on understanding their well-documented kinking nonlinear elastic (KNE) behavior and the role of their inherently layered crystalline structure. The fundamental insight gained from these atomistic studies will allow for better engineering of MAX phases to fully take advantage of their unique properties and enable extensions to other layered materials as well.
N-7: Effect of Additional Elements on Deformation Mechanism of γ-TiAl: Ji Young Kim1; Jong-hun Kim2; Jae-Kwon Kim2; Taegu Lee3; Seung-Hwa Ryu3; Dong-chan Jang3; Eun Soo Park4; Seong-Woong Kim2; Seung-Eon Kim2; 1Korea Institute of Materials Science; Seoul National University; 2Korea Institute of Materials Science; 3Korea Advanced Institute of Science and Technology; 4Seoul National University
TiAl alloys have been studied widely as promising candidates for high-temperature applications due to high specific strength and excellent high-temperature properties. However, because of low ductility at room temperature, the applications of γ-TiAl have been hindered. Although numerous studies using alloy design strategies have been performed to improve the room temperature ductility, there is a lack of studies which clarify the effect of composition on deformation mechanism. In the present study, we investigated deformation mechanism depending on additional elements (Nb, Cr) using micro-pillar compression test in scanning electron microscope. Prior to the experiments, we predicted deformation mechanism depending on additional elements and loading directions using molecular dynamic simulation considering stacking fault energy and schmid factor. This study provides theoretical basis for understanding the effect of additional elements on deformation mechanism of γ-TiAl. Furthermore, it is expected to be used as a novel guideline for alloy design with excellent mechanical properties.
N-9: Grain Boundary Engineering Leading to Enhanced Mechanical Properties of Superhard Boron Carbide: Qi An1; Dezhou Guo1; Kolan Reddy2; 1University of Nevada, Reno; 2Shanghai Jiao Tong University
To improve the mechanical properties of superstrong B4C, we investigated how grain boundaries (GBs) determine the deformation and failure mechanism of B4C. The deformation and failure mechanism of nanocrystalline B4C (n-B4C) were studied using the reactive force field (ReaxFF) simulations. We found that the main deformation mechanism of nanocrystalline B4C is grain boundary sliding, leading to a reverse Hall-Petch relationship. This GB sliding triggers the amorphous shear band formation at predistorted icosahedral GB regions with initiation of cavitation within the amorphous bands. Our simulation results are validated by the nanoindentation experiments in which an intergranular amorphous GB phase was observed due to GB sliding. Although most GB sliding events in our ReaxFF simulations lead to the intergranular amorphization, we do observe one intragranular amorphization initiates from grain boundaries (GBs) and propagates along the rhombohedral (011)[2-1-1] slip system. This leads to the amorphous shear band formation and intragranular amorphization.
N-10: Highly-impermeable and Stretchable Encapsulation with Wavy Structure: Hangeul Kim1; Na-Hyang Kim1; Hansol Jeon1; Han Gi Chae1; Ju-Young Kim1; 1UNIST
To ensure chemical stability and long-term operation, organic electronic devices require encapsulations with low water vapor transmittance rate. A thermally-grown silicon dioxide, oxidized from single-crystalline silicon wafer at high temperature, has an ultra-low water vapor transmittance rate due to a high density without pinholes and defects. However, the thermally-grown silicon dioxide has low an elastic limit and shows a brittle fracture. For that reasons, it is necessary to improve a stretchability of the thermally-grown silicon dioxide thin film for stretchable encapsulation. Therefore, by applying a wavy structure to the thermally-grown silicon dioxide, we improved the stretchability. We fabricated a wavy structured thermally-grown silicon dioxide by oxidizing wavy textured single-crystalline silicon wafer. We carried out tensile test and cyclic tensile test by using a nano universal testing machine to analyze the stretchability. Lastly, we discussed about the correlation between the improvement of stretchability and the wavy structure through a FEM analysis.
N-11: In-situ Tensile Test in TEM for High Precision Measurement of Mechanical Behavior and Quantitative Dislocation Motion Correlation with Single Crystal Ni: Xiaoqing Li1; John Turner2; Karen Bustillo2; Rohan Dhall2; Andrew Minor1; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory
With the development of electron microscopy, material research aiming at smaller scales had been prevailed. However, nanoscale samples tests have poor repeatability, because their shape and behaviors are harder to control. In this work, in situ TEM mechanical tests of Nickel samples on push-to-pull device were performed in order to determine the precise load-elongation behavior of the dog-bone segment, to match the local plasticity and dislocation motion in that area. Pre-stretching tests were performed to starch the sample to a perfect flat condition before the actual mechanical test. Two “markers”, a free-standing gap, were designed for measuring the precise elongation of the dog-bone segment. Using frame-by-frame digital image analysis for each test, the dislocation motions in dog-bone area and the “marker” distance can be measured. After highlighting all the dislocation motions from the recorded videos, each movement can be matched with the displacement change of the dog-bone.
Cancelled
N-12: Interfacial Mechanics and Reconstruction on Graphene-metal Surfaces: Kaihao Zhang1; Mitisha Surana1; Ganesh Ananthakrishnan1; Matthew Poss1; Pascal Pochet2; Harley Johnson1; Sameh Tawfick1; 1University of Illinois Urbana Champaign; 2Institute for Nanoscience and Cryogenics
The interfaces between graphene and the underlying substrate are of critical importance not only in the applications of graphene in electronic devices, but also to the mechanical behavior of graphene-based composites. It is well-established that an electronic band gap opens in graphene synthesized on strongly-interacting metals such as Pd. Nonetheless, the intricate structure-mechanics of the graphene-metal interfaces are unclear. In this study, we examine the surface reconstructions of Pd substrates during graphene synthesis to probe the mechanisms driving their various morphologies. Orientation-dependent surface step-bunching and terraces are observed on Pd surface. We characterize these surfaces by Electron-Backscatter Diffraction (EBSD) combined with Atomic Force Microscopy (AFM) and Raman spectroscopy. The surface reconstructions are found to be related to the planar miscut angle of Pd, lattice and thermal expansion coefficients mismatch during graphene synthesis on the Pd catalyst. The step’s morphology and Raman signatures are strongly dependant on the Pd surface orientation.
N-13: Mechanical Properties of Electrochemically Lithiated Tin: Chung Su Hong1; Seung Min Han1; 1KAIST
Sn has emerged as one of the most promising Li ion battery anode due to its high theoretical capacity to replace the conventional graphite anodes in lithium ion batteries. With its low melting point and low modulus and strength, Sn has the ability to relax stresses via plasticity and creep deformations that occur during lithitation/delithiation cycling. However, to understand these mechanical behavior problems, FEM modeling is required, but the accuracy of these mechanical properties of lithiated Sn is uncertain. In this study, nanoindentation experiments on lithiated Sn was performed under the protection of mineral oil to obtain accurate measurements of hardness and modulus of different phases of lithiated Sn. Supporting other research, Young’s modulus and the hardness of lithiated tin are found to decline with increasing lithium content. The fully lithiated Sn phase, Li22Sn5 was determined to be 26.3 GPa, which is lower than the reported value.
N-14: Microstructural Analysis and Mechanical Behavior of Ultrafine-grained Ni-Y-Zr Alloys: Shruti Sharma1; Samuel Moehring1; Pedro Peralta1; 1Arizona State University
Ultrafine-grained alloys (with grain size between 250-1000nm) such as Cu-Cr-Zr alloys are state-of-the-art materials with potential applications in the field of energy and defense due to their improved mechanical properties. However, these alloys suffer intrinsic weaknesses owing to the properties of their alloying elements (low melting point of Cu). This work focused on developing microstructurally-stable ultrafine-grained Ni-Y-Zr alloys that alleviate such weaknesses by using Nickel for its high melting point, ductility and formability, and Zr and Y, for their ability to produce precipitate in Ni matrix that can enhance strength and stability. Samples were synthesized via arc-melting and characterized using EDS and EBSD to ascertain elemental composition and map-out crystallographic relationships between matrix and precipitates. Annealing heat treatments performed on the samples ensured the stability of precipitates, and uniaxial tension and compression tests reported the quasi-static properties. Furthermore, correlation of mechanical behavior was established with the microstructure of the alloys.
N-16: Pseudoelastic Response and Shape Memory Behavior in Ceramic Materials: Hamed Hosseini-Toudeshki1; Steven Herrera2; David Kisailus2; Olivia Graeve1; 1University of California, San Diego; 2University of California, Riverside
We describe the pseudoelastic response and shape memory behavior of LaNbO4 ceramic materials under compressive forces utilizing nano-indentation. Shape memory ceramics are smart materials with unique properties and diverse applications such as mechanical damping systems, actuation and sensors. Compared with alloys, ceramics offer valuable advantages such as the ability to operate at higher temperatures. Smart ceramic materials with pseudoelastic mechanical behavior have gained attention recently due to their unusual reversible response upon uniaxial stresses or thermal loads without fracture. In this study, two different pseudoelastic responses have been observed (step-like response and rubber-like behavior) on single crystal and polycrystalline pillars of LaNbO4. A combination of shape memory behavior (under thermal loads) and pseudoelastic cycles (under mechanical loads) up to 10% recoverable strain are achieved during micro-compression experiments. To avoid mismatch stresses during phase transformation, experiments were performed on micrometer-sized pillars fabricated from bulk ceramics using focused ion beam technology.
N-17: Role of Tantalum Concentration and Processing Temperature on Tensile Behavior of Nanocrystalline Copper-tantalum Alloys: Soundarya Srinivasan1; Chaitanya Kale1; Scott Turnage1; Billy Hornbuckle2; Kris Darling2; Kiran Solanki1; 1Arizona State University; 2US Army Research Laboratory
Microstructural instability in traditional nanocrystalline materials limits the understanding of the fundamental effect of nanocrystalline grain size on the mechanical behavior under extreme environmental conditions such as high temperatures and loading rates. In this work, we study the interplay between the Ta concentrations, and processing temperatures on the resulting microstructure of a powder processed Cu-Ta alloy along with the tensile behavior at different strain rates. Varying Ta concentration and processing temperature resulted in different micro-structured Cu-Ta alloys with grain sizes ranging from the nanocrystalline to the ultrafine-grained regimes. Transmission electron microscopy was used on the as-processed and the deformed samples to characterize the microstructure pre – and post – deformation. Results show that the Cu-Ta alloys having nanocrystalline grain size show increase in tensile ductility as the strain rate is increased from quasi-static (10-3 s-1) to dynamic (103 s-1) strain rates.
N-18: Strength Recovery in Self-healed Nanoporous Gold: Eun-Ji Gwak1; Hansol Jeon1; Ju-Young Kim1; 1UNIST
Nanoporous gold (np-Au) is an open-cell structured material with nanoscale pores and ligament introducing high surface area and high surface curvature. Np-Au shows mechanical fragility with low strength and brittleness due to its irregular porous structure introducing catastrophic failure under tensile stress. During failure, deformed ligaments are localized near fracture surface and each ligament on fracture surface failed by necking. Recent studies have suggested cold-welding behavior of gold nanowires with diameter of sub-10 nm at room temperature. Two nanowires could be welded by surface diffusion because surface diffusion rate is increased by reducing diameter of nanowires. Based on this, fracture surface of np-Au could be self-healed while it consists of very thin fractured ligament like nanowires.Here, self-healing ability of np-Au is suggested in terms of strength recovery. Np-Au samples are fabricated free-corrosion dealloying and mechanical properties before and after self-healing are investigated by in-situ tensile test in SEM chamber.
N-19: Stress-strain Responses from Small Scale Testing (Nanoindentation, In-situ Micro-compression, Micro-tension) in Pure Magnesium: Skye Supakul1; Tolin Skov-Black1; Keenan O'Neill1; Scout Garrison1; Job Rodriguez1; Josiah Dowell1; 1University of Nevada, Reno
This study was a part of the undergraduate senior design project in the Materials Science & Engineering department at the University of Nevada, Reno. The senior design students utilized an array of small-scale testing techniques – such as spherical nano-indentation, micro-pillar compression and micro tensile experiments – to characterize the elastic isotropy, plastic anisotropy, and compression-tension asymmetry in large (millimeter sized) individual grains of pure magnesium. The indentation stress-strain response was analyzed as a function of varying indenter radii (5, 10 and 100 um). These results were compared to more uniaxial loading scenarios such as Focused Ion Beam fabricated micro-pillar compression and micro-tensile tests to identify yield strength and strain hardening behavior. Local crystal lattice orientations were measured by electron backscatter diffraction. The results are discussed in terms of advantages and limitations of each technique to capture elastic isotropy, plastic anisotropy, and compression-tension asymmetry in pure magnesium.
N-20: Thickness-dependent Elastic Deformation Limit of Thermally-grown SiO2 Thin Films: Na-Hyang Kim1; Hangeul Kim1; Ju-Young Kim1; 1Ulsan National Institute of Science and Technology
In long-term stability, however, most of these organic devices are vulnerable to moisture, oxygen, etc. To prevent the moisture in the air, highly dense film is required as a barrier. In this research, we studied thermally grown SiO2 film as an encapsulation film as we expected thermally grown silicon dioxide film to have ultra-low water permeability and high elasticity due to its rare defects, high density and high uniformity. We increased elastic deformation limit of thermally grown silicon dioxide film to apply on stretchable devices. To increase elastic deformation limit, the thickness of thermally grown SiO2 films were decreased to observe thickness effect. Although thick SiO2 films show very short elastic deformation limit around 0.7%, thinner SiO2 films have smaller size and number of defects, and these features are characterized as high elastic deformation limit. Tensile tests were performed on those films to discuss thickness-dependent on elastic deformation limit.
Cancelled
N-21: Ultra-strong and Ductile Nb-nanowire/NiTi-based-matrix Nanocomposite via Strain Induced Transformation: Yuxuan Chen1; Kaiyuan Yu1; Lishan Cui1; 1China University of Petroleum Beijing
A Nb-nanowire/NiTiFe-matrix nanocomposite was fabricated by conventional casting, forging and wire drawing. BCC Nb nanowires of ~ 15×60×1500 nm in dimension distribute uniformly within the NiTiFe matrix of B2 (CsCl) structure. Tensile tests show that the nanocomposite obtains apparent yield strength of ~ 2.2 GPa and uniform elongation of 13%, superior to all other nanocomposites reported to date. In situ synchrotron XRD reveals that the matrix deforms by dislocation slip along with strain induced martensitic transformation upon yielding and that the nanowires exhibit a maximum elastic strain of 4.5%. In situ TEM results suggest that the strain induced transformation at the vincinity of the nanowire/matrix interfaces may be responsible for the concurrently high strength and ductility of the nanocomposite.