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A comparative study on microstructure,nanomechanical and corrosion behaviors of AlCoCuFeNi high entropy alloys fabricated by selective laser melting and laser metal deposition

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Journal of Materials Science & Technology 2022年第36期131卷 221-230页

作者： Yaojia Ren Hong Wu Bin Liu Yong Liu Sheng Guo ZBJiao Ian Baker State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China Department of Industrial and Materials Science Chalmers University of TechnologyGothenburg SE-41296Sweden Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHong Kong 999077China Thayer School of Engineering Dartmouth CollegeHanover NH 03755-8000United States

The present study investigated the microstructure,nanomechanics,and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting(SLM)and laser metal deposition(LMD).The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix(^90μm in width)and Cu-rich twinned FCC phase.The columnar grains grew epitaxially along the building direction and exhibited a strong{001}texture.In comparison,a coarse columnar-grained BCC matrix(^150μm in width)with a strongertexture,rod-like B2 precipitates,and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect.Consequently,the LMD-processed specimens showed a lower hardness,wear resistance,and corrosion resistance,but higher creep resistance and reduced Young's modulus than the SLM-processed specimens.Hot cracks occurred in both types of specimens,which could not be completely suppressed due to Cu segregation.

关键词： Selective laser melting Laser metal deposition High entropy alloys nanomechanics Corrosion

Nonlinear stochastic dynamics of an array of coupled micromechanical oscillators

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International Journal of Mechanical System Dynamics 2023年第1期3卷 3-11页

作者： Maria I.Katsidoniotaki Ioannis Petromichelakis Ioannis A.Kougioumtzoglou Department of Civil Engineering and Engineering Mechanics Columbia UniversityNew YorkNew YorkUSA

The stochastic response of a multi‐degree‐of‐freedom nonlinear dynamical system is determined based on the recently developed Wiener path integral(WPI)technique.The system can be construed as a representative model of electrostatically coupled arrays of micromechanical oscillators,and relates to an experiment performed by Buks and Roukes.Compared to alternative modeling and solution treatments in the literature,the paper exhibits the following novelties.First,typically adopted linear,or higher‐order polynomial,approximations of the nonlinear electrostatic forces are circumvented.Second,for the first time,stochastic modeling is employed by considering a random excitation component representing the effect of diverse noise sources on the system dynamics.Third,the resulting high‐dimensional,nonlinear system of coupled stochastic differential equations governing the dynamics of the micromechanical array is solved based on the WPI technique for determining the response joint probability density function.Comparisons with pertinent Monte Carlo simulation data demonstrate a quite high degree of accuracy and computational efficiency exhibited by the WPI technique.Further,it is shown that the proposed model can capture,at least in a qualitative manner,the salient aspects of the frequency domain response of the associated experimental setup.

关键词： Wiener path integral nonlinear system stochastic dynamics nanomechanics

Natural overlaying behaviors push the limit of planar cyclic deformation performance in few-layer MoS_(2) nanosheets

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InfoMat 2023年第9期5卷 64-77页

作者： Peifeng Li Guangjie Zhang Zhuo Kang Xin Zheng Yong Xie Chunyuan Liang Yizhi Zhang Xiaoyang Fang Rong Sun Zhiquan Liu Yeqiang Bu Yang Lu Yue Zhang Shenzhen Institute of Advanced Electronic Materials Shenzhen Institute of Advanced TechnologyChinese Academy of SciencesShenzhenthe People's Republic of China CAS Key Laboratory of Standardization and Measurement for Nanotechnology CAS Center for Excellence in NanoscienceNational Center for Nanoscience and TechnologyBeijingthe People's Republic of China Beijing Advanced Innovation Center for Materials Genome Engineering Beijing Key Laboratory for Advanced Energy Materials and TechnologiesUniversity of Science and Technology BeijingBeijingthe People's Republic of China State Key Laboratory for Advanced Metals and Materials School of Materials Science and EngineeringUniversity of Science and Technology BeijingBeijingthe People's Republic of China College of Chemistry and Materials Engineering Zhejiang A&F UniversityHangzhouthe People's Republic of China Center for X-mechanics School of Aeronautics and AstronauticsZhejiang UniversityHangzhouPeople's Republic of China Department of Mechanical Engineering The University of Hong KongHong Kongthe People's Republic of China

As a typical two-dimensional(2D)transition metal dichalcogenides(TMDCs)material with nonzero band gap,MoS_(2)has a wide range of potential applications as building blocks in the field of nanoelectronics.The stability and reliability of the corresponding nanoelectronic devices depend critically on the mechanical performance and cyclic reliability of 2D MoS_(2).Although an in situ technique has been used to analyze the mechanical properties of 2D materials,the cyclic mechanical behavior,that is,fatigue,remains a major challenge in the practical application of the devices.This study was aimed at analyzing the planar cyclic performance and deformation behavior of three-layer MoS_(2)nanosheets(NSs)using an in situ transmission electron microscopy(TEM)variable-amplitude uniaxial low-frequency and cyclic loading-unloading tensile acceleration test.We also elucidated the strengthening effect of the natural overlaying affix fragments(other external NSs)or wrinkle folds(internal folds from the NS itself)on cycling performances and service life of MoS_(2)NSs by delaying the whole process of fatigue crack initiation,propagation,and fracture.The results have been confirmed by molecular dynamics(MDs)simulations.The overlaying enhancement effect effectively ensures the long-term reliability and stability of nanoelectronic devices made of few-layer 2D materials.

关键词： cyclic deformation performance few-layer MoS_(2) in situ TEM nanomechanics natural overlays strengthening effect

Diamond semiconductor and elastic strain engineering

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Journal of Semiconductors 2022年第2期43卷 35-46页

作者： Chaoqun Dang Anliang Lu Heyi Wang Hongti Zhang Yang Lu Department of Mechanical Engineering City University of Hong KongHong KongChina School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China Department of Materials Science and Engineering City University of Hong KongHong KongChina Nano-Manufacturing Laboratory(NML) Shenzhen Research Institute of City University of Hong KongShenzhen 518057China

Diamond,as an ultra-wide bandgap semiconductor,has become a promising candidate for next-generation microelec-tronics and optoelectronics due to its numerous advantages over conventional semiconductors,including ultrahigh carrier mo-bility and thermal conductivity,low thermal expansion coefficient,and ultra-high breakdown voltage,etc.Despite these ex-traordinary properties,diamond also faces various challenges before being practically used in the semiconductor industry.This review begins with a brief summary of previous efforts to model and construct diamond-based high-voltage switching diodes,high-power/high-frequency field-effect transistors,MEMS/NEMS,and devices operating at high temperatures.Following that,we will discuss recent developments to address scalable diamond device applications,emphasizing the synthesis of large-area,high-quality CVD diamond films and difficulties in diamond doping.Lastly,we show potential solutions to modulate diamond’s electronic properties by the“elastic strain engineering”strategy,which sheds light on the future development of diamond-based electronics,photonics and quantum systems.

关键词： diamond optoelectronics power electronics nanomechanics elastic strain engineering

Enhanced tensile ductility of tungsten microwires via high-density dislocations and reduced grain boundaries

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Journal of Materials Science & Technology 2021年第36期95卷 193-202页

作者： Chaoqun Dang Weitong Lin Fanling Meng Hongti Zhang Sufeng Fan Xiaocui Li Ke Cao Haokun Yang Wenzhao Zhou Zhengjie Fan Ji-jung Kai Yang Lu Department of Mechanical Engineering City University of Hong KongHong KongChina Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhenChina School of Physical Science and Technology ShanghaiTech UniversityShanghaiChina Nano-Manufacturing Laboratory(NML) Shenzhen Research InstituteCity University of Hong KongShenzhenChina State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong UniversityXi'anChina Centre for Advanced Nuclear Safety and Sustainable Development City University of Hong KongHong KongChina

Despite being strong with many outstanding physical properties,tungsten is inherently brittle at room temperature,restricting its structural and functional applications at small scales.Here,a facile strategy has been adopted,to introduce high-density dislocations while reducing grain boundaries,through electron backscatter diffraction(EBSD)-guided microfabrication of cold-drawn bulk tungsten wires.The designed tungsten microwire attains an ultralarge uniform tensile elongation of~10.6%,while retains a high yield strength of~2.4 GPa.in situ TEM tensile testing reveals that the large uniform elongation of tungsten microwires originates from the motion of pre-existing high-density dislocations,while the subsequent ductile fracture is attributed to crack-tip plasticity and the inhibition of grain boundary cracking.This work demonstrates the application potential of tungsten microcomponents with superior ductility and workability for micro/nanoscale mechanical,electronic,and energy systems.

关键词： Tungsten Dislocation Grain boundary Ductility In situ TEM nanomechanics

High elasticity of CsPbBr_(3) perovskite nanowires for flexible electronics

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Nano Research 2021年第11期14卷 4033-4037页

作者： Xiaocui Li You Meng Rong Fan Sufeng Fan Chaoqun Dang Xiaobin Feng Johnny C.Ho Yang Lu Department of Mechanical Engineering City University of Hong KongHong Kong999077China Department of Materials Science and Engineering City University of Hong KongHong Kong999077China School of Automotive Engineering Dalian University of TechnologyDalian116024China Nano-Manufacturing Laboratory(NML) Shenzhen Research Institute of City University of Hong KongShenzhen518057China

Due to the enhanced ambient structural stability and excellent optoelectronic properties, all-inorganic metal halide perovskite nanowires have become one of the most attractive candidates for flexible electronics, photovoltaics and optoelectronics. Their elastic property and mechanical robustness become the key factors for device applications under realistic service conditions with various mechanical loadings. Here, we demonstrate that high tensile elastic strain (∼ 4% to ∼ 5.1%) can be achieved in vapor-liquid-solid-grown single-crystalline CsPbBr_(3) nanowires through in situ scanning electron microscope (SEM) buckling experiments. Such high flexural elasticity can be attributed to the structural defect-scarce, smooth surface, single-crystallinity and nanomechanical size effect of CsPbBr_(3) nanowires. The mechanical reliability of CsPbBr_(3) nanowire-based flexible photodetectors was examined by cyclic bending tests, with no noticeable performance deterioration observed after 5,000 cycles. The above results suggest great application potential for using all-inorganic perovskite nanowires in flexible electronics and energy harvesting systems.

关键词： perovskite nanowire CsPbBr_(3) nanomechanics in situ testing elasticity flexible electronics

Compressive deformation of ultralong amyloid fibrils

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Acta Mechanica Sinica 2010年第6期26卷 977-986页

作者： Raffaella Paparcone Steven Cranford Markus J.Buehler Laboratory for Atomistic and Molecular Mechanics

Involved in various neurodegenerative diseases, amyloid fibrils and plaques feature a hierarchical structure, ranging from the atomistic to the micrometer scale.At the atomistic level,a dense and organized hydrogen bond network is resembled in a beta-sheet rich secondary structure, which drives a remarkable stiffness in the range of 10-20GPa,larger than many other biological nanofibrils, a result confirmed by both experiment and theory.However, the understanding of how these exceptional mechanical properties transfer from the atomistic to the nanoscale remains unknown.Here we report a multiscale analysis that, from the atomistic-level structure of a single fibril,extends to the mesoscale level,reaching size scales of hundreds of nanometers.We use parameters directly derived from full atomistic simulations of Aβ（1-40） amyloid fibrils to parameterize a mesoscopic coarse-grained model,which is used to reproduce the elastic properties of amyloid fibrils.We then apply our mesoscopic model in an analysis of the buckling behavior of amyloid fibrils with different lengths and report a comparison with predictions from continuum beam theory. An important implication of our results is a severe reduction of the effective modulus due to buckling,an effect that could be important to interpret experimental results of ultralong amyloid fibrils.Our model represents a powerful tool to mechanically characterize molecular structures on the order of hundreds of nanometers to micrometers on the basis of the underlying atomistic behavior.The work provides insight into structural and mechanical properties of amyloid fibrils and may enable further analysis of larger-scale assemblies such as amyloidogenic bundles or plaques as found in disease states.

关键词： Amyloid Coarse-grain Molecular simulation nanomechanics Materiomics

Small scale effects on buckling and postbuckling behaviors of axially loaded FGM nanoshells based on nonlocal strain gradient elasticity theory

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Applied Mathematics and Mechanics(English Edition) 2018年第4期39卷 561-580页

作者： S.SAHMANI A.M.FATTAHI Department of Mechanical Engineering Bandar Anzali Branch Islamic Azad University Department of Mechanical Engineering Tabriz Branch Islamic Azad University

By means of a comprehensive theory of elasticity, namely, a nonlocal strain gradient continuum theory, size-dependent nonlinear axial instability characteristics of cylindrical nanoshells made of functionally graded material(FGM) are examined. To take small scale effects into consideration in a more accurate way, a nonlocal stress field parameter and an internal length scale parameter are incorporated simultaneously into an exponential shear deformation shell theory. The variation of material properties associated with FGM nanoshells is supposed along the shell thickness, and it is modeled based on the Mori-Tanaka homogenization scheme. With a boundary layer theory of shell buckling and a perturbation-based solving process, the nonlocal strain gradient load-deflection and load-shortening stability paths are derived explicitly. It is observed that the strain gradient size effect causes to the increases of both the critical axial buckling load and the width of snap-through phenomenon related to the postbuckling regime, while the nonlocal size dependency leads to the decreases of them. Moreover, the influence of the nonlocal type of small scale effect on the axial instability characteristics of FGM nanoshells is more than that of the strain gradient one.

关键词： nanomechanics functionally graded material(FGM) nonlocal strain gradient theory nonlinear instability perturbation technique

Nanomechanical behaviors of (110) and (111) CdZnTe crystals investigated by nanoindentation

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Rare Metals 2009年第6期28卷 570-575页

作者： LI Yan KANG Renke GAO Hang WANG Jinghe LANG Yanjua Key Laboratory of the Ministry of Education of China for Precision and Nan-Traditional Machining Technology Dalian University of Technology Dalian 116024 China Precision Engineering Research Institute Harbin Institute of Technology Harbin 150001 China

The nanomechanical behaviors of （110） and （111 ） CdZnTe crystals were investigated by nanoindentation. It was found that the indenter tip was adhered by the removed materials in scanning testing area although the scanning force on the tested surface was very small （1000 nN）, which would affect the testing result of nanoindentation, so the indenter was clean before nanoindentation test. The experimemtal results showed that the hardness and Young＇s modulus decreased with the increase of indentation loads on the same plane. Because of the anisotropy of the CdZnTe crystal, the average hardness of （110） plane is 35% lower than that of （111） plane, and there are about 30% difference of the hardness along different crystallographic directions on the same plane. The hardness in 0° and 120° testing directions was the same due to the threefold symmetry of a Berkovich indenter. And the anisotropy affected the surface quality during machining of CdZnTe crystal.

关键词： nanomechanics anisotropy nanoindentation CdZnTe