Mechanical Behavior at the Nanoscale V: Size Effects
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
Monday 2:30 PM
February 24, 2020
Room: Santa Rosa
Location: Marriott Marquis Hotel
Session Chair: Yu Zou, University of Toronto; Alice Lassnig, Austrian Academy of Sciences
2:30 PM
Mechanical Behavior of Metallic Glass-HCP Crystalline Nanolayers: Mohammad Abboud1; Amir Motallebzadeh2; Sezer Ozerinc1; 1Middle East Technical University; 2Koç University
Nanolayered metallic glass-crystalline structures provide an effective approach to improving the low ductility of monolithic metallic glasses. Previous work on metallic glass-FCC crystalline nanolayers has shown that the strength of these nanolayers is dominated by the response of the softer crystalline phase. As a result, the strength increases with decreasing layer thickness, resembling the Hall-Petch behavior. In this work, we investigated metallic glass-HCP crystalline nanolayers such as CuTi/Ti and CuZr/Zr, and observed that the strength does not vary with layer thickness. Furthermore, the strength is virtually the same as that of the corresponding monolithic metallic glass (CuZr and CuTi). We attribute this interesting behavior to the higher strength of the HCP phase when compared to the metallic glass, as predicted by the confined-layer slip model. The results show that the mechanical behavior of metallic glass-crystalline composites strongly depends on the crystal structure and the relative strengths of the layers.
2:50 PM
Effect of Layer Spacing on Mechanical Properties of Cu/Co Nanolaminates Through Tensile Testing: Rohit Berlia1; Paul Rasmussen1; Santhosh Rajarajan1; Jagannathan Rajagopalan1; 1Arizona State University
The deformation behavior of nanostructured metallic multilayers has been extensively investigated because of their superior mechanical properties, primarily via nanoindentation and micropillar compression experiments. Here, we report tensile measurements on Cu/Co nanolaminates with four different layer spacings (2nm, 4nm, 8nm, 16nm), but similar film thickness. The nanolaminate was synthesized using magnetron sputtering at room temperature and tensile loading-unloading cycles were performed on freestanding samples parallel to the Cu/Co interface using MEMS devices. Cross-sectional TEM and XRD measurements showed the transition from the presence of coherency at the Cu/Co interface in smaller spacing to loss of coherency in higher spacing films. The yield strength of nanolaminates is inversely dependent on the square root of layer thickness. Furthermore, an inelastic strain recovery was also observed in all the films both during and after unloading, with further recovery occurring upon heating. Negligible effect of layer spacing was observed on elastic modulus.
3:10 PM
Size Effect of NiTi-based Shape Memory Nanoparticles on Recoverable Strain: Ji Young Kim1; So Yeon Kim2; Jin Woo Kim2; Won Seok Ko3; Eun Soo Park1; 1Seoul National University; 2Seoul National University; Massachusetts Institute of Technology; 3Ulsan University
It is well known that martensitic phase transformation in shape memory alloys (SMAs) exhibit grain size and sample size dependence. In particular, studies on the size effect have attracted great attention because signal of shape memory behavior disappears below the critical size. However, previous studies have limited to the practical application such as composite materials since researchers used single crystals to study the sample size effect. In the present study, we suggested novel method to fabricate isotropic polycrystalline SMA nanoparticles and investigated size effect of these nanoparticles. We systematically performed thermal analysis and mechanical tests in scanning electron microscope to understand martensitic transformation behavior and carefully compared with the data of molecular dynamic simulation to analyze the mechanical behavior of the nanoparticles. This study provides theoretical basis to fabricate isotropic polycrystalline SMA nanoparticles and novel guideline for studying SMA size effect, which can accelerate the practical use of these materials.
3:30 PM Invited
Grain Size Effect on Thin Film Adhesion: Alice Lassnig1; 1Erich Schmid Institute of Materials Science
Thin film adhesion is a crucial measure to determine the reliability of a thin film – substrate materials system. In the following study we investigated the role of film grain size of sputtered Cu films deposited on glass substrates, as a model material system. While maintaining residual stresses, interface chemistry, and film thickness comparable, the film microstructures were varied by means of different sputtering parameters as well as isothermal annealing after deposition. Highly compressively stressed Mo overlayers were used to cause delamination of the thin films from the substrates allowing to quantify thin film adhesion using the Hutchinson & Suo model. It could be shown that the thin films with smaller grains revealed improved adhesion compared to their large grained counterparts. Furthermore, an in-situ TEM crack propagation study was conducted to visualize the crack-grain boundary interaction between the thin film and the substrate material.
4:10 PM Break
4:30 PM
Tension-compression Asymmetry in Plasticity of Nanoporous Gold: Hansol Jeon1; Eun-Ji Gwak1; Hangeul Kim1; Ju-Young Kim1; 1UNIST
Mechanical behavior of nanoporous gold (np-Au) has been extensively studied by nanoindentation test, but systemic analysis on the deformation of np-Au in both tension and compression is not fully carried out. In this study, we investigated mechanical behavior of np-Au in tension and compression. By preparing micro-scale samples without grain boundaries and cracks, we could focus on the mechanical properties only. Three np-Au samples were prepared and the mechanical tests were performed using in-situ push-to-pull (P-to-P) devices for tensile testing and with the nanoindenter for compressive testing. We found two significant things related with tension-compression asymmetry; (1) the tensile yield strengths are higher than the compressive yield strengths and (2) the size effect exponent n in σy ∝ dL^-n where σy is the yield strength and dL is average ligament size is greater in compression. We discuss the effect of loading mode on deformation and size effect in strength.
4:50 PM
Fracture Properties of Ultrafinegrain Chromium at RT: Dislocations Processes and Toughening Mechanisms: Inas Issa1; Anton Hohenwarter1; Reinhard Fritz1; Daniel Kiener1; 1Montanuniversitat Leoben
Scale-bridging fracture experiments on ultrafine-grained chromium (UFG, Cr) are performed at different length scales, starting from macroscale over microscale (in situ SEM) down to nanoscale (in situ TEM). A quantitative assessment of the fracture toughness yields ∼3 MPa.m1/2 in the frame of LEFM. In situ TEM tests reveal explicitly the occurrence of dislocation emission processes and related crack tip blunting serving as toughening mechanisms before intercrystalline fracture in UFG bcc metals. In relation to coarse-grained Cr, in situ TEM tests demonstrate the importance of strengthening grain boundaries (GBs) as promising strategy in promoting further ductility and toughening in UFG bcc metals. By adding adhesion improving impurities such as Carbon or Boron, we modify the atomistic GBs configuration in front of the notch and will present how local segregation affects GBs cohesion and fracture toughness.
5:10 PM
Studying the Anisotropic Deformation of Sapphire in Different Crystallographic Orientations using Nanoindentation and Micropillar Compression: Anugraha Thyagatur Kidigannappa1; Alex Montagne2; Xavier Maeder2; Johann Michler2; Veronica Trabadelo3; Fatemeh Saeidi2; M. Parlinska-Wojtan4; Kilian Wasmer2; Siddhartha Pathak1; 1university of Nevada Reno; 2EMPA – Swiss Federal Laboratories for Materials Testing and Research; 3Mohammed VI Polytechnic University, Materials Science and Nano-engineering Department; 4 Institute of Nuclear Physics, Polish Academy of Sciences
Single crystal sapphire has hexagonal close-packed crystal structure hence exhibits mechanical anisotropy in different orientations. In this work deformation behavior and crack propagation of single crystal sapphire in four crystallographic orientations: <10 –10>, <1 – 210>, <0001> and <-1012>, corresponding to M, A, C and R planes respectively, were systematically studied using nanoindentation with spherical indenters of 1 μm and 10 μm radius, and micropillar compression. Indentation and micropillar compression data reveal that the R plane was more prone to deform plastically as compared to other planes. The residual deformations of the four planes were analyzed using Schmid law and geometric observations. Indentation stress-strain curves were also utilized to understand the origin and anisotropic behavior of pop-ins in the various crystallographic planes using cumulative statistics.
5:30 PM
Exploring Small-scale Quasicrystal Plasticity in Unknown Temperature Regimes: Yu Zou1; 1University of Toronto
Quasicrystals, sometimes, can be regarded as an intermediate state between regular metals (crystal) and metallic glasses (amorphous), in terms of structural and chemical complexity. A long-standing problem, however, significantly impedes practical usage of quasicrystals: steady-state plastic deformation has only been found at high temperatures or under confining hydrostatic pressures; at low and intermediate temperatures, they are very brittle, suffer from low ductility and formability and, consequently, their deformation mechanisms are still not clear. Here, this presentation systematically studies the deformation behavior of icosahedral Al-Pd-Mn and decagonal Al-Ni-Co quasicrystals using a micro-thermomechanical technique over a range of temperatures (25-500 °C), strain rates, and sample sizes accompanying microstructural analysis. Here we show interesting phenomena relevant to small-length scales, including: cracking, serrated flows, diffusion and phase transformation.