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Polarization pinning at antiphase boundaries in multiferroic YbFeO_(3)

Chinese Physics B 2024年第11期33卷 39-45页

作者： Guodong Ren Pravan Omprakash Xin Li Yu Yun Arashdeep S.Thind Xiaoshan Xu Rohan Mishra Institute of Materials Science and Engineering Washington University in St.LouisSt.LouisMO 63130USA Department of Physics and Astronomy University of NebraskaLincolnNE 68588USA Department of Mechanical Engineering & Mechanics Drexel UniversityPhiladelphiaPA 19104-2875USA Nebraska Center for Materials and Nanoscience University of NebraskaLincolnNE 68588USA Department of Mechanical Engineering and Material Science Washington University in St.LouisSt.LouisMO 63130USA

The switching characteristics of ferroelectrics and multiferroics are influenced by the interaction of topological defects with domain *** report on the pinning of polarization due to antiphase boundaries in thin films of the multiferroic hexagonal YbFeO_(3).We have directly resolved the atomic structure of a sharp antiphase boundary(APB)in YbFeO_(3) thin films using a combination of aberration-corrected scanning transmission electron microscopy(STEM)and total energy calculations based on density-functional theory(DFT).We find the presence of a layer of FeO_(6) octahedra at the APB that bridges the adjacent *** imaging shows a reversal in the direction of polarization on moving across the APB,which DFT calculations confirm is structural in nature as the polarization reversal reduces the distortion of the FeO_(6) octahedral layer at the *** APBs in hexagonal perovskites are expected to serve as domain-wall pinning sites and hinder ferroelectric switching of the domains.

关键词： hexagonal ferrites ferroelectric multiferroic topological defect STEM

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Mechanism of solute hardening and dislocation debris-me diate d ductilization in Nb-Si alloy

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Journal of materials science & Technology 2024年第36期203卷 167-179页

作者： Bo-Qing Li Irene J.Beyerlein Shuhei Shinzato Shigenobu Ogata Wei-Zhong Han Center for Advancing Materials Performance from the Nanoscale State Key Laboratory for Mechanical Behavior of MaterialsXi’an Jiaotong UniversityXi’an 710049China Materials Department University of CaliforniaSanta BarbaraCA 93106-5070USA Department of Mechanical Engineering University of CaliforniaSanta BarbaraCA 93106-5070USA Department of Mechanical Science and Bioengineering Osaka UniversityOsaka 560-8531Japan

Niobium(Nb)is sensitive to even minute quantities of silicon(Si)solutes,which are known to induce pronounced ***,the underlying mechanism for hardening remains elusive since the ef-fect of Si solutes on dislocation behavior is ***,using tensile testing,in-situ microscopy and nanomechanical testing,the behavior of dislocations in dilute Nb-Si alloys,containing from 0 at.%to 0.8 at.%Si,is *** show that the hardness,strength and strain hardening rate increase from two to four times,while the uniform elongation in tension only reduces 50%as the Si content *** evolve from complex entangled patterns in Nb to parallel long-straight screw dislocation-dominated structures in Nb-Si ***-situ indentation reveals that the origins of the marked harden-ing in Nb-Si alloy are the reduction of dislocation mobility and cross-slip *** densities of dislocation debris-superjogs and loops introduced throughout the sample during warm rolling and an-nealing are found to provide active internal dislocation sources,which explain the minimal ductility loss seen in these Nb-Si *** findings can help guide the alloy design of high-performance refractory materials for extreme temperature applications.

关键词： Niobium Si solute Hardening Ductilization Dislocation

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Magnetic properties and magnetocaloric effects in Eu(Ti,Nb,Mn)O_(3) perovskites

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Journal of Rare Earths 2024年第8期42卷 1560-1567,I0006页

作者： Junfeng Wang Huicai Xie Quanyi Liu Zhihong Hao Zhaojun Mo Qi Fu Xinqiang Gao Jun Shen Ganjiang Innovation Academy Chinese Academy of SciencesGanzhou341119China Faculty of Materials Metallurgy and Chemistry Jiangxi University of Science and TechnologyGanzhou341000China School of Rare Earth and New Materials Engineering Gannan University of Science and TechnologyGanzhou341000China Department of Energy and Power Engineering School of Mechanical EngineeringBeijing Institute of TechnologyBeijing100081China

In perovskite EuTiO_(3),the magnetic characteristics and magnetocaloric effect(MCE) can be flexibly regulated by converting the magnetism from antiferromagnetic to *** the present work,a series of Eu(Ti,Nb,Mn)O_(3) compounds,abbreviated as ETNMO for convenience of description,was fabricated and their crystallography,magnetism together with cryogenic magnetocaloric effects were systematically *** crystallographic results demonstrate the cubic perovskite structure for all the compounds,with the space group of *** magnetic phase transitions are observed in these second-order phase transition(SOPT) *** joint substitution of elements Mn and Nb can considerably manipulate the magnetic phase transition process and magnetocaloric performance of the ETNMO *** the Mn content increases,gradually widened-ΔS_(M)-T curves are obtained,and two peaks with a broad shoulder are observed in the-ΔS_(M)-T curves for Δμ_(0)H≤0-1 *** a field change of 0-5 T,the values of maximum magnetic entropy change(-ΔS_(M)^(max)) and refrigeration capacity(RC) are evaluated to be 34.7 J/(kg·K) and 364.9 J/kg for EuTi_(0.8625)Nb_(0.0625)Mn_(0.075)O_(3), 27.8 J/(kg·K) and367.6 J/kg for EuTi_(0.8375)Nb_(0.0625)Mn_(0.1)O_(3),23.2 J/(kg·K) and 369.2 J/kg for EuTi_(0.8125)Nb_(0.0625)Mn_(0.125)O_(3),17.1 J/(kg·K) and 357.6 J/kg for EuTi_(0.7875)Nb_(0.0625)Mn_(0.15)O_(3),*** co nsiderable MCE parameters make the ETNMO compounds potential candidates for cryogenic magnetic refrigeration.

关键词： ETNMO perovskites Cryogenic refrigeration Magnetic phase transition Magnetocaloric effect Rare earths

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Understanding the Thermal Impedance of Silicone Rubber/Hexagonal Boron Nitride Composites as Thermal Interface materials

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Chinese Journal of Polymer science 2024年第3期42卷 352-363,I0008页

作者： Yuan Ji Shi-Da Han Hong Wu Shao-Yun Guo Feng-Shun Zhang Jian-Hui Qiu The State Key Laboratory of Polymer Materials Engineering Sichuan Provincial Engineering Laboratory of Plastic/Rubber Complex Processing TechnologyPolymer Research InstituteSichuan UniversityChengdu 610065China Institute of Chemical Materials China Academy of Engineering PhysicsMianyang 621900China Department of Mechanical Engineering Faculty of Systems Science and TechnologyAkita Prefectural UniversityAkita 015-0055Japan

Silicone rubber(SR) composites are most widely used as thermal interface materials(TIMs) for electronics heat dissipation. Thermal impedance as the main bottleneck limiting the performance of TIMs is usually neglected. Herein, the thermal impedance of SR composites loaded with different levels of hexagonal boron nitride(h-BN) as TIMs was elaborated for the first time by the ASTM D 5470 standard test and finite element analysis. It was found that elastic modulus and surface roughness of SR composites increased with the increase of h-BN content, indicating that the conformity was reduced. When the assembly pressure was 0.69 MPa, there existed an optimal h-BN content at which the contact resistance was minimum(0.39 K·cm^(2)·W^(-1)). Although the decreased bond line thickness(BLT) by increasing the assembly pressure was beneficial to reduce the thermal impedance, the proper assembly pressure should be selected to prevent the warpage of the contact surfaces and the increase in contact resistance, according to the compression properties of the SR composites. This study provides valuable insights into fabrication of high-performance TIMs for modern electronic device applications.

关键词： Thermal interface materials Hexagonal boron nitride Thermal impedance Surfaces

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Strengthening mechanism and forming control of linear friction welded GH4169 alloy joints

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Chinese Journal of Aeronautics 2024年第4期37卷 609-626页

作者： Yu SU Xiawei YANG Tingxi MENG Xinyuan HE Dong WU Wenya LI Shuo YIN State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Shaanxi Key Laboratory of Friction Welding Technologies School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Department of Mechanical Manufacturing and Biomedical EngineeringParsons BuildingTrinity College DublinThe University of DublinDublin 2Ireland

Numerical simulation and experimental research on Linear Friction Welding(LFW) for GH4169 superalloy were carried out. Based on the joint microstructure and mechanical properties,a suitable welding process was determined, which provided an important theoretical basis for the manufacture and repair of aeroengine components such as the superalloy blisk. The results show that the joint strain rate gradually increases with the increase of welding frequency, and the deformation resistance of the thermoplastic metal increases in the welding process, resulting in the interface thermoplastic metal not being extruded in time to form a flash, so the joint shortening amount gradually decreases. The thermoplastic metal in the center of the welding surface is kept at high welding temperature for a long time, resulting in the decrease of the joint strength. The microhardness of the joint shows a “W” distribution perpendicular to the weld, and most of the joints break in the Thermo-mechanically Affected Zone(TMAZ) with high tensile strength and low *** the welding area is increased without changing the aspect ratio of the welding surface, the interface peak temperature increases gradually, and the joint shortening amount decreases with the increase of the welding interface size.

关键词： Linear Friction Welding(LFW) Microstructure mechanical properties Numerical simulation Joint shortening amount

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Ultrafast relaxation dynamics of excited carriers in metals: Simplifying the intertwined dependencies upon scattering strengths, phonon temperature, photon energy, and excitation level

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Physical Review B 2024年第18期109卷 184310-184310页

作者： D. M. Riffe Richard B. Wilson Mechanical Engineering Department and Materials Science and Engineering Department

Using the Boltzmann transport equation (BTE), we study the evolution of nonequilibrium carrier distributions in simple (sp) metals, assumed to have been instantaneously excited by an ultrafast laser pulse with photon energy hν. The mathematical structure of the BTE scattering integrals reveals that hν is a natural energy scale for describing the dynamics. Normalizing all energy quantities by hν leads to a set of three unitless parameters β/δ, γ, and α that control the relaxation dynamics: β/δ is the normalized ratio of electron-phonon to electron-electron scattering strengths, γ is the normalized phonon (lattice) temperature, and α is the normalized absorbed energy density. Using this theory, we systematically investigate relaxation times for the high-energy part of the distribution (τH), energy transfer to the phonon subsystem (τE), and intracarrier thermalization (τth). In the linear region of response (valid when α is sufficiently small), we offer heuristic descriptions of each of these relaxation times as functions of β/δ and γ. Our results as a function of excitation level α show that many ultrafast experimental investigations lie in a transition region between low excitation (where the relaxation times are independent of α) and high excitation (where the two-temperature model of carrier dynamics is valid). Approximate boundaries that separate these three regions are described by simple expressions involving the normalized parameters of our model.

关键词： Carrier dynamics Electron relaxation Lifetimes & widths

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Numerical simulations of ship collision with offshore UHPC structures 9th

Numerical simulations of ship collision with offshore UHPC s...

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9th International Conference on Collision and Grounding of Ships and Offshore Structures, ICCGS 2023

作者： Sha, Yanyan Department of Mechanical and Structural Engineering and Materials Science University of Stavanger Stavanger Norway

ISBN: (纸本)9781032611303

Reinforce concrete (RC) structures have been used to construct various types of offshore structures in the past decades. Reinforce concrete has many advantages such as high strength, relatively low cost, and easy maintenance. Therefore, reinforced concrete has been used to construct the supporting structures of offshore platforms, wind turbines, and floating bridges. Nonetheless, offshore reinforced concrete structures are under the threat of collision loads from service and passing ships. Since offshore reinforced concrete structures are typically thin-walled structures, one major issue is the punching shear damage of such structures under ship collision loads. Recently, ultra-high-performance concrete (UHPC) has been increasingly used for onshore structures. UHPC has demonstrated higher impact resistance than ordinary reinforced concrete. However, research on UHPC structures under ship collision loads has seldom been conducted. In this paper, numerical simulations of ship collision with thin-walled UHPC structures are conducted using detailed finite element models. The application of different UHPC material models on ship collision simulations is discussed. The response of UHPC and normal RC structures are also compared. It is found that with calibrated parameters, the CSCM material model in LS-DYNA can be used for modelling UHPC in ship collision simulations. The results show that using UHPC material can effectively increase the ship collision resistance of offshore structures compared with ordinary reinforced concrete. © 2024 The Author(s).

关键词： Reinforced concrete

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Accelerating the prediction of stacking fault energy by combining ab initio calculations and machine learning

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Physical Review B 2024年第21期109卷 214102-214102页

作者： Albert Linda Md. Faiz Akhtar Shaswat Pathak Somnath Bhowmick Department of Materials Science and Engineering Department of Mechanical Engineering

Stacking fault energies (SFEs) are key parameters to understand the deformation mechanisms in metals and alloys, and prior knowledge of SFEs from ab initio calculations is crucial for alloy design. Machine learning (ML) algorithms used in the present work show a ∼ 80 times acceleration of generalized stacking fault energy predictions, which are otherwise computationally very expensive to get directly from density functional theory calculations, particularly for alloys. The origin of the features used for training the ML algorithms lies in the physics-based Friedel model, and the present work uncovers the connection between the physics of d electrons and the deformation behavior of transition metals and alloys. Predictions based on the ML model agree with the experimental data. Our model can be helpful in accelerated alloy design by providing a fast method of screening materials in terms of stacking fault energies.

关键词： Stacking faults Density functional calculations Machine learning

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Ultimate and residual strength assessments of intact and collision damaged columns of the Bjørnafjorden floating bridge 9th

Ultimate and residual strength assessments of intact and col...

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9th International Conference on Collision and Grounding of Ships and Offshore Structures, ICCGS 2023

作者： Yu, Zhaolong Wang, Xintong Moan, Torgeir Amdahl, Jørgen Sha, Yanyan Norway Department of Mechanical and Structural Engineering and Materials Science University of Stavanger Norway

ISBN: (纸本)9781032611303

The Norwegian Public Road Administration (NPRA) has initiated an ambitious project to replace the current ferry crossing solutions with floating bridges over the wide and deep Norwegian fjords. This will substantially reduce the travelling time among major cities in Norway. It is found that ship collisions represent major critical loads to the safety and integrity of floating bridges that governs the structural design. This paper investigates the ultimate and residual strength of columns in an initial design of the Bjørnafjorden floating bridge before and after ship collisions with an initial kinetic energy of 125 MJ and 150 MJ respectively corresponding to a 10,000-year event as estimated from risk assessment. The ultimate bending and torsional capacities are assessed. Three different approaches are adopted, (1) the nonlinear finite element method using LS-DYNA;(2) A semi-analytical code PULS based on energy methods;(3) DNV rules-based formulations. The results are compared and discussed. © 2024 The Author(s).

关键词： Structural design

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Dealloying of an amorphous TiCuRu alloy results in a nanostructured electrocatalyst for hydrogen evolution reaction

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Carbon Energy 2023年第8期5卷 87-97页

作者： Jinsen Tian Yuanchao Hu Wenfei Lu Jiahua Zhu Xiaodi Liu Jun Shen Gang Wang Jan Schroers College of Mechatronics and Controlling Engineering Shenzhen UniversityShenzhenChina Shenzhen Key Laboratory of High Performance Nontraditional Manufacturing College of Mechatronics and Control EngineeringShenzhen UniversityShenzhenChina Department of Mechanical Engineering&Materials Science Yale UniversityNew HavenConnecticutUSA Department of Inorganic Materials School of Materials Science and EngineeringTongji UniversityShanghaiChina Laboratory for Microstructures Institute of MaterialsShanghai UniversityShanghaiChina

Development of an electrocatalyst that is cheap and has good properties to replace conventional noble metals is important for H_(2) *** this study,dealloying of an amorphous Ti_(37)Cu_(60)Ru_(3) alloy was performed to prepare a freestanding nanostructured hydrogen evolution reaction(HER)*** effect of dealloying and addition of Ru to TiCu alloys on the microstructure and HER properties under alkaline conditions was investigated.3 at.%Ru addition in Ti_(40)Cu_(60) decreases the overpotential to reach a current density of 10mA cm^(-2) and Tafel slope of the dealloyed samples to 35 and 34mV dec−*** improvement of electrocatalytic properties was attributed to the formation of a nanostructure and the modification of the electronic structure of the ***-principles calculations based on density function theory indicate that Ru decreases the Gibbs free energy of water *** work presents a method to prepare an efficient electrocatalyst via dealloying of amorphous alloys.

关键词： amorphous alloy dealloying first-principles calculations HER TiCuRu

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