Mechanical Behavior at the Nanoscale V: In-Situ Testing II
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
Wednesday 2:00 PM
February 26, 2020
Room: Santa Rosa
Location: Marriott Marquis Hotel
Session Chair: Gregory Thompson, University of Alabama; Scott Mao, University of Pittsburgh
2:00 PM Invited
Influence of Mechanical Loading on Nanocrystalline Stabilized Alloys: Gregory Thompson1; Jonathan Priedeman1; Thomas Koenig1; Xuyang Zhou1; B. Chad Hornbuckle2; Kris Darling2; Sean Fudger2; Ankit Gupta3; Garritt Tucker3; 1University of Alabama; 2Army Research Laboratory; 3Colorado School of Mines
The partitioning of solutes to nanocrystalline grain boundaries (GBs) has shown the ability to mitigate grain growth. This stability mechanism is either as a reduction of the thermodynamic GB energy and/or a kinetic constraint of the GBs by pinning. In the vast majority of studies, stability has been explicitly investigated as a function of temperature. This work extends these investigations to mechanical loading. The first case is Cu(Nb), an alloy that has shown thermal stabilization. Upon loading at 200C, 400C, and 600C, the alloy exhibits a reduction in strength. In contrast, Cu(Ta) does not show this trend, with these two alloys to be compared. A complementary study of Ni(P) will then be discussed. Depending upon the prior heat treatment, the Ni(P) can either exhibit thermodynamic or Zener pinning stabilization enabling a single alloy type to compare different stability mechanisms with respect to mechanical loading effects.
2:40 PM
Quantitative Analysis on Deformation of a Cu/Cu45Zr55 Multilayered Structure Combining In-Situ Transmission Electron Microscopy and a Finite Element Model: Yucong Gu1; Qianying Guo1; Gregory Thompson1; Lin Li1; 1University of Alabama
We perform a quantitative analysis on the deformation of an amorphous Cu45Zr55/crystalline Cu multilayer, combining in-situ transmission electron microscopy and a finite element model (FEM). The experimental load-displacement curve upon indenting the multilayer exhibits an elastic-perfect plastic flow. The top amorphous layer accommodates the deformation via severe strain localization, indicative of shear banding; while the crystalline layers undergo grain rotation, recorded by precession electron diffraction. The FEM replicates the experimental setup, reproducing the load-displacement curve before perfect plastic flow, and detailing the stress field underneath indenter that initiates the incipient plasticity. The FEM results suggest that despite the higher stress concentration in the top amorphous layer, the crystalline layer is likely to yield first. Catastrophic shear bands form after the micro-yielding of top crystalline and amorphous layers. Deformation vector field from FEM suggests the global texture change and grain rotation are the direct results of indentation-induced deformation.
3:00 PM
Probing the Deformation Mechanisms of Al-matrix Composites with Small-scale Mechanical Testing: Olivia Donaldson1; Jenna Wardini1; Timothy Rupert1; 1University of California, Irvine
Metal matrix composites (MMCs) have emerged as important materials in the aerospace and automotive industries. These materials deform in interesting ways, due to a combination of hard and soft phases that are mixed together. To facilitate an understanding of the deformation mechanisms and the importance of interfaces inside the material, in situ mechanical testing in the scanning electron microscope is used here to elucidate deformation mechanisms from the nanoscale to the microscale. Micron-sized pillars of Al-5Zn-1.5Mg-0.4Mn-0.2Cu-0.2Zr reinforced with SiC particles were compressed to determine the interplay between the two main phases, followed by the isolation of individual internal interfaces. Analysis of the material following failure showed dispersed secondary phases, precipitates, intermetallics, and boundary enrichment. The Al-SiC interfaces were found to be particularly important, allowing us to develop new design rules for the incorporation of SiC particles within an Al-alloy matrix in order to limit slip band formation.
3:20 PM
Effects of Microstructures on Superelasticity of CaFe2As2 Single Crystal: Shuyang Xiao1; John Sypek1; Sriram Vijayan1; Paul Canfield2; Mark Aindow1; Seok-Woo Lee1; 1University of Connecticut; 2Ames Laboratory & Department of Physics and Astronomy
The superelasticity of CaFe2As2 are strongly affected by defect structures. Understanding the role of defects can help improve its superelastic performance. In this study, we investigated the effects of microstructure on the superelasticity of [0 0 1]-oriented CaFe2As2 micropilllar using the in-situ micromechanical testing and transmission electron microscopy. Three different microstructures were prepared. An Sn-solution grown sample is nearly defect free and was used as a control sample. An quenched FeAs-solution grown sample has a dense rectangular network of screw dislocations which causes low-angle twist distortion, leading to the suppression of superplasticity. An annealed FeAs-solution grown sample fractured at a lower stress due to the presence of stress concentrator, nanoscale FeAs precipitates. In sum, superelasticity of CaFe2As2 is significantly influenced by defect structures, and our research outcomes will be generally useful to enhance the superelastic performance in ThCr2Si2-type intermetallic compounds which have the same type of crystal structure.
3:40 PM Break
4:00 PM
Ductile Deformation of Nearly Monoatomic Metallic Glass: Mehrdad Kiani1; Wendy Gu1; 1Stanford University
Metallic glasses (MGs) exhibit a size-dependent brittle-to-ductile transition where deformation occurs according to homogenous flow rather than shear bands. This behavior has been observed for numerous MGs independent of composition and atomic structure. Here, we present in situ SEM compressions of nearly monoatomic nickel nanoparticles with unusual plastic behavior. These nanoparticles are synthesized colloidally by rapidly reducing metallic ions. Synchrotron X-ray diffraction shows the nanoparticles have a large free volume (>6%). 90 nm Ni nanoparticles exhibit two regions in the compressive force-displacement curve: linear elastic-plastic loading followed by a non-linear increase in force. 190 nm Ni nanoparticles exhibit the same initial region but different second region characterized by undulations in the force-displacement curve. In both sizes, at most one rapid slip event is observed at the transition between the two regions. We relate this deformation behavior to the high free volume in monoatomic MGs and mechanisms for shear band propagation.
4:20 PM
Microstructure Characterization and Micro-mechanical Properties of 14YWT Processed With Different Methods: Cayla Harvey1; Osman El-Atwani2; Stuart Maloy2; Sid Pathak1; 1University of Nevada, Reno; 2Los Alamos National Laboratory
Microstructure characterization and micro-mechanical testing and has been carried out on 14YWT nanostructured ferritic alloys processed under various thermo-mechanical paths (hot extrusion and hydrostatic extrusion with various annealing temperatures). These alloys are a leading candidate for fast nuclear reactors operating at high temperatures. Electron backscatter diffraction was used to identify the principle texture and microstructure components. Transmission electron microscopy was used to characterize the morphology, dislocation density, and oxide particles. Novel in-situ micro-pillar compression and micro-tensile testing in a scanning electron microscope at various temperatures (25, 300, 600°C) was used to determine the mechanical behavior and deformation mechanisms. Results will compare the properties with respect to the underlying microstructure and processing conditions, as well as be compared to previous macro-scale results on similarly processed on 14YWT.
4:40 PM Cancelled
Small Scaled Plasticity in Reversed Hall-patch Region: Scott Mao1; Xiang Wang1; 1University of Pittsburgh
Recent works indicated the deformation of small-volume materials below a critical size would switch to be controlled by the competition between diffusive plasticity and displacive plasticity. However, the effect of diffusive activities on the material’s strength remains little investigated. Here, the strength-size relationship in silver and platinum nanocrystals from dozens to several nanometers were collectively studied by in-situ transmission electron microscopy. Dislocation activities were still observed in below-10 nm samples in tension testing, different with the pure diffusion mechanism like “Coble Creep”. The yielding strength of small-volume materials is defined as the nucleation stress for the first dislocation. The lowered strength with the decreasing of the sample size originated from the surface diffusion-assisted dislocation nucleation, presenting as the inverse Hall-Petch relation in silver. And diffusibility decides the different strength-size relations in two materials. The reversed Hall-Petch relation showed here enriches understanding of small scaled plasticity in small-volume materials.
5:00 PM Cancelled
Extraordinary Tension-compression Asymmetry in Submicron-sized Amorphous Silicon: Yuecun Wang1; Lin Tian2; Evan Ma3; Zhiwei Shan1; 1Center for Advancing Materials Performance from the Nanoscale, Xian Jiaotong University; 2Institute of Materials Physics, University of Göttingen; 3Department of Materials Science and Engineering, Johns Hopkins University
The extraordinary tension-compression asymmetry in strength, anelasticity, and plasticity has been found in the submicron-sized amorphous Si (a-Si), which is one of the most important amorphous semiconductor materials and the model material for covalent network studies, tested by quantitative nanomechanics. We proposed a scenario based on the negative activation volume of shear events in a-Si, which can be activated in compression but not in tension. The in-situ mechanical-electrical coupling tests validates that transformation from the semiconductive low-density a-Si to the denser and more metallic-and liquid-like a-Si (regarded as the plasticity carriers) occurs in compression rather than tension. Our findings reveal the structure-mechanical behaviors of a-Si under both tension and compression, as well as broaden our understanding on the directionally-bonded disordered solids’ structure and its response under applied stress.