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Mechanism of subsurface microstructural fatigue crack initiation during high and very-high cycle fatigue of advanced bainitic steels

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Journal of Materials Science & Technology 2022年第13期108卷 142-157页

作者： Guhui Gao Rong Liu Yusong Fan Guian Qian Xiaolu Gui R.D.k.Misra Bingzhe Bai Material Science&Engineering Research Center School of MechanicalElectronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044China State key Laboratory of Nonlinear Mechanics(LNM) Institute of MechanicsChinese Academy of SciencesBeijing 100190China Laboratory for Excellence in Advanced Steel Research Department of MetallurgicalMaterials and Biomedical EngineeringUniversity of Texas at El Paso500W University AvenueEl PasoTX 79968USA key Laboratory of Advanced Material School of Material Science and EngineeringTsinghua UniversityBeijing 100084China

Advanced bainitic steels with the multiphase structure of bainitic ferrite,retained austenite and martensite exhibit distinctive fatigue crack initiation behavior during high cycle fatigue/very high cycle fatigue(HCF/VHCF)*** subsurface microstructural fatigue crack initiation,referred to as“non-inclusion induced crack initiation,NIICI”,is a leading mode of failure of bainitic steels within the HCF/VHCF *** this regard,there is currently a missing gap in the knowledge with respect to the cyclic response of multiphase structure during VHCF failure and the underlying mechanisms of fatigue crack initiation during *** address this aspect,we have developed a novel approach that explicitly identifies the knowledge gap through an examination of subsurface crack initiation and interaction with the local *** was accomplished by uniquely combining electron microscopy,three-dimensional confocal microscopy,focused ion beam,and transmission kikuchi ***,the study indicated that there are multiple micro-mechanisms responsible for the NIICI failure of bainitic steels,including two scenarios of transgranular-crack-assisted NIICI and two scenarios of intergranular-crack-assisted NIICI,which resulted in the different distribution of fine grains in the crack initiation *** fine grains were formed through fragmentation of bainitic ferrite lath caused by localized plastic deformation or via local continuous dynamic recrystallization because of repeated interaction between slip bands and prior austenite grain *** formation of fine grains assisted the advancement of small *** important aspect discussed is the role of retained austenite(RA)during cyclic loading,on crack initiation and propagation in terms of the morphology,distribution and stability of RA,which determined the development of localized cyclic plastic deformation in multiphase structure.

关键词： Microstructure Advanced bainitic steels Very high cycle fatigue Mechanism Retained austenite

Quantum Transport across Amorphous-Crystalline Interfaces in Tunnel Oxide Passivated Contact Solar Cells: Direct versus Defect-Assisted Tunneling

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Chinese Physics Letters 2021年第3期38卷 75-80页

作者： Feng Li Weiyuan Duan Manuel Pomaska Malte köhler kaining Ding Yong Pu Urs Aeberhard Uwe Rau College of Science Nanjing University of Posts and TelecommunicationsNanjing 210023China IEk-5 Photovoltaik Forschungszentrum Jülich52425 JülichGermany

Tunnel oxide passivated contact solar cells have evolved into one of the most promising silicon solar cell concepts of the past decade,achieving a record efficiency of 25%.We study the transport mechanisms of realistic tunnel oxide structures,as encountered in tunnel oxide passivating contact(TOPCon) solar *** transport is affected by various factors,including oxide layer thickness,hydrogen passivation,and oxygen *** the thickness of the tunnel oxide layer increases,a faster decline of conductivity is obtained computationally than that observed *** tunneling seems not to explain the transport characteristics of tunnel oxide ***,it can be shown that recombination of multiple oxygen defects in a-SiOx can generate atomic silicon nanowires in the tunnel ***,new and energetically favorable transmission channels are generated,which dramatically increase the total current,and could provide an explanation for our experimental *** work proves that hydrogenated silicon oxide(SiOx:H) facilitates high-quality passivation,and features good electrical conductivity,making it a promising hydrogenation material for TOPCon solar *** carefully selecting the experimental conditions for tuning the SiOx:H layer,we anticipate the simultaneous achievement of high open-circuit voltage and low contact resistance.

关键词： tuning Tunnel conductivity

Microstructure evolution and deformation mechanism of amorphous/crystalline high-entropy-alloy composites

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Journal of Materials Science & Technology 2020年第19期54卷 14-19页

作者： Jia Li Haotian Chen Hui Feng Qihong Fang Yong Liu Feng Liu Hong Wu Peter k Liaw State key Laboratory of Advanced Design and Manufacturing for Vehicle Body Hunan UniversityChangsha 410082China State key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China Department of Materials Science and Engineering The University of TennesseeKnoxvilleTN 37996USA

High-entropy amorphous alloys present high hardness,but low tensile ***,deformation behavior of the amorphous/crystalline Fe Co Cr Ni high-entropy alloy(HEA)composite prepared by the previous experiment is investigated using atomic *** result shows the partial dislocations in the crystal HEA layer,and the formation of shear bands in the amorphous HEA layer occurs after *** strength of the amorphous/crystalline HEA composite reduces with increasing the thickness of the amorphous layer,agreeing with the previous *** coupled interaction between the crystal plasticity and amorphous plasticity in amorphous/crystalline HEA composites results in a more homogeneous redistribution of plastic deformation to cause interface hardening,due to the complex stress field in the amorphous *** current findings provide the insight into the deformation behavior of the amorphous/crystalline HEA composite at the nanoscale,which are useful for optimizing the structure of the HEA composite with high strength and good plasticity.

关键词： High-entropy alloy Amorphous/crystalline composite Deformation behavior Strengthening mechanism Molecular dynamics

Green synthesis of pure and doped semiconductor nanoparticles of ZnS and CdS

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Transactions of Nonferrous Metals Society of China 2015年第10期25卷 3265-3270页

作者： k.MURALEEDHARAN Vijisha k.RAJAN V.M.ABDUL MUJEEB Department of Chemistry University of Calicut

Nanoparticles of pure and Cu/Ag-doped CdS and ZnS have been synthesized via chemical bath deposition without using any capping or toxic *** synthesis was carried out through a simple and less expensive green *** XRD result shows that both pure CdS and ZnS and their doped derivatives are of high crystalline with hexagonal packing *** average crystalline size of all nanoparticles was calculated using Debye-Scherrer *** crystalline size of nanoparticles of pure samples varied with that of the doped *** average crystalline sizes of all nanoparticles are found to be in the range of 5.5-2.2 nm for CdS（from pure to doped） and 4.3-3.4 nm for ZnS,*** band gap values obtained from UV-visible spectra are in the range of 3.5-2.1 e V for CdS and 3.3-2.7 e V for ZnS derivatives,*** FTIR spectral data give characteristic peaks for Cd—S,Cu—S,Ag—S and Zn—S bonds and confirm the formation of respective *** peaks corresponding to the microstructural formation are also *** FE-SEM images show the granular morphological structure for all the *** agglomeration size of the samples in the range of 10-50 nm for CdS：Cu and 50-100 nm for ZnS：Cu is observed.

关键词： chalcogenide ZnS CdS nanostructure semiconductor green synthesis catalytic properties

A novel semi-active TMD with folding variable stiffness spring

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Earthquake Engineering and Engineering Vibration 2014年第3期13卷 509-518页

作者： M.H.Rafi eipour A.k.Ghorbani-Tanha M.Rahimian R.Mohammadi-Ghazi Department of Civil Engineering Science and Research Branch Islamic Azad University Tehran 39187-97717 Iran School of Civil Engineering College of Engineering University of Tehran P.O.Box 11155-4563 Tehran Iran Department of Civil and Environmental Engineering Massachusetts Institute of Technology Cambridge MA USA Formerly with School of Civil Engineering College of Engineering University of Tehran P.O.Box 11155-4563 Tehran Iran

An innovative variable stiffness device is proposed and investigated based on numerical simulations. The device, called a folding variable stiffness spring （FVSS）, can be widely used, especially in tuned mass dampers （TMDs） with adaptive stiffness. An important characteristic of FVSS is its capability to change the stiffness between lower and upper bounds through a small change of distance between its supports. This special feature results in lower time-lag errors and readjustment in shorter time intervals. The governing equations of the device are derived and simplified for a symmetrical FVSS with similar elements. This device is then used to control a single-degree-of-freedom （SDOF） structure as well as a multi-degree-of-freedom （MDOF） structure via a semi-active TMD. Numerical simulations are conducted to compare several control cases for these structures. To make it more realistic, a real direct current motor with its own limitations is simulated in addition to an ideal control case with no limitations and both the results are compared. It is shown that the proposed device can be effectively used to suppress undesirable vibrations of a structure and considerably improves the performance of the controller compared to a passive device.

关键词： semi-active tuned mass damper variable stiffness folding variable stiffness spring

Constructing on-demand single/multi-color transitioning fabrics with photocatalysis/photothermal-armed deficient semiconductors

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Nano Research 2024年第5期17卷 3633-3643页

作者： Daniel k.Macharia Shamima Sarker Meng Liu Zeyulong Wen Nuo Yu Meifang Zhu Zhigang Chen State key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringDonghua UniversityShanghai 201620China

On-demand color switching systems that utilize synchronized semiconductor-catalyzed reduction and photothermal-accelerated oxidation in liquid/solid are highly ***,on-demand single/multi-color switching fabrics have been constructed by using defective SnO_(2):Sb-based color switching ***_(2):Sb nanocrystals with the suitable doping concentration accord lattices with abundant free electrons,conferring high photocatalytic and photothermal performances.A well-crafted set of dual light-responsive semiconductor-catalyzed systems with rapid color change can be attained via the homogenous mixture of SnO_(2):Sb with suitable redox dyes to produce single-color(RGB(red,green,blue))and multi-color transitioning(purple and green)*** illumination of these systems by 450 nm light triggers rapid photocatalytic discoloration,while irradiation by 980 nm light confers the photothermal effect that accelerates recoloration in ***,the inks can be extended to rewritable fabrics by embedding the nanocrystals and redox dyes into hydroxyethyl cellulose(as the polymer matrix)and then coating on hydrophobic cotton fabrics to produce photo-switchable fabrics with excellent single/multi-color *** exploiting the dual light interactions with the semiconductor-mediated systems,various images/letters can be remotely printed and erased on the rewritable fabrics which show promise for potential applications as information storage media and visual ***,the present rewritable fabric shows good stability and *** present work provides insights into the development of novel color-switching materials.

关键词： color switching defective semiconductor photocatalysis photothermal rewritable fabrics

Utilizing Multilayer Design of Organic-Inorganic Hybrids to Enhance Wearable Strain Sensor in Humid Environment

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Chinese Journal of Polymer Science 2023年第7期41卷 1037-1050页

作者： Chen-Chen Lu Wei-Chen Gao Peng Li Wei Wu Robert k.Y.Li Hui Zhao Guangxi key Laboratory of Clean Pulp&Papermaking and Pollution Control School of Light Industry and Food EngineeringGuangxi UniversityNanning530004China Guangxi key Laboratory of Calcium Carbonate Resources Comprehensive Utilization College of Materials and Chemical EngineeringHezhou UniversityHezhou542899China Department of Materials Science and Engineering City University of Hong KongTat Chee AvenueKowloonHong Kong999077China

Flexible strain wearable sensors have attracted considerable attention due to their advantages of low cost, lightweight, high sensitivity and good flexibility. However, the strain sensors are easy to be damaged in an extreme humidity environment or by the wearer’s sweat in the process of use, resulting in detection disorder or even a short circuit. Furthermore, preparation of sensors with stable properties under extreme environments is one of the most important research directions. To fill this gap, a flexible sensor was prepared by using polyurethane and carbon nanotubes, then modified by polydopamine and 1H,1H,2H,2H-perfluorodecane-mercaptan. A typical tunnel model was used to explain the working mechanism of the sensor, the sensitivity of the sensor is also explained and evaluated by the tunneling theory. The results show that the sensor has good sensitivity (the sensor has a stable sensing signal output under a strain range from 2% to 300%) and stability over 8500 cycles. At the same time, the sensor has good superhydrophobicity, the water contact angle reaches 152°, and it is still stable in a humid environment. Moreover, this sensor shows excellent performance in monitoring human joint motion (such as finger, elbow, wrist and knee) and physiological signals (such as speaking and drinking). This work provides an effective design method for the sensor which can be applied in a high humidity environment.

关键词： Wearable strain sensor Polyurethane Carbon nanotubes Superhydrophobicity

Laser surface treatment-introduced gradient nanostructured TiZrHfTaNb refractory high-entropy alloy with significantly enhanced wear resistance

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Journal of Materials Science & Technology 2022年第15期110卷 43-56页

作者： Jiasi Luo Wanting Sun Ranxi Duan Wenqing Yang k.C.Chan Fuzeng Ren Xu-Sheng Yang Department of Industrial and Systems Engineering Advanced Manufacturing Technology Research CentreThe Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina Department of Materials Science and Engineering Southern University of Science and TechnologyShenzhen 518055China The Hong kong Polytechnic University Shenzhen Research Institute Shenzhen 518060China

Heterogeneous gradient nanostructured metals have been shown to achieve the strength-ductility synergy, thus potentially possessing the enhanced tribological performance in comparison with their homogeneous nanograined counterparts. In this work, a facile laser surface remelting-based surface treatment technique is developed to fabricate a gradient nanostructured layer on a TiZrHfTaNb refractory highentropy alloy. The characterization of the microstructural evolution along the depth direction from the matrix to the topmost surface layer shows that the average grain size in the ~100 μm-thick gradient nanostructured layer is dramatically refined from the original ~200 μm to only ~8 nm in the top surface layer. The microhardness is therefore gradually increased from ~240 HV in matrix to ~650 HV in the topmost surface layer, approximately 2.7 times. Noticeably, the original coarse-grained single-phase bodycentered-cubic TiZrHfTaNb refractory high-entropy alloy is gradually decomposed into TiNb-rich bodycentered-cubic phase, TaNb-rich body-centered-cubic phase, ZrHf-rich hexagonal-close-packed phase and TiZr Hf-rich face-centered-cubic phase with gradient distribution in grain size along the depth direction during the gradient refinement process. As a result, the novel laser surface treatment-introduced gradient nanostructured TiZrHfTaNb refractory high-entropy alloy demonstrates the significantly improved wear resistance, with the wear rate reducing markedly by an order of magnitude, as compared with the as-cast one. The decomposed multi-phases and gradient nanostructures should account for the enhanced wear resistance. Our findings provide new insights into the refinement mechanisms of the laser-treated refractory high-entropy alloys and broaden their potential applications via heterogeneous gradient nanostructure engineering.

关键词： Laser surface treatment Refractory high-entropy alloy Gradient nanostructure Wear resistance High-resolution transmission electron microscopy

Inhibiting effect of I-phase formation on the plastic instability of the duplex structured Mg-8Li-6Zn-1.2Y(in wt.%)alloy

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Journal of Magnesium and Alloys 2023年第6期11卷 2196-2204页

作者： B.J.Wang D.k.Xu X.Q.Zhuang L.Y.Sheng School of Environmental and Chemical Engineering Shenyang Ligong UniversityShenyang110159China key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang110016China Peking University Shenzhen InstituteShenzhen Key Lab Human Tissue Regenerate&RepairShenzhen 518057China

In this work,the tensile behaviors of Mg-8%Li and Mg-8%Li-6%Zn-1.2%Y alloys at ambient temperature were investigated and *** revealed that the plastic instability of Mg-8%Li alloy was quite remarkable and the variation range of serrated flowing stress can reach5 *** the Mg-8%Li-6%Zn-1.2%Y alloy,the formation of I-phase(Mg_(3)Zn_(6)Y)can simultaneously enhance the tensile strength and eliminate the plastic instability phenomenon,whilst its ductility was *** in-situ tensile tests revealed that for the Mg-8%Li alloy,the severity and number of slip traces present in bothα-Mg andβ-Li matrix phases increased remarkably with the applied tensile ***,slip traces were quite fine inβ-Li matrix phase and could be clearly observed when the applied tensile strain exceeded 18%.Due to the incompatibility of plastic deformation occurred in two matrix phases,the induced strain concentration atα-Mg/β-Li interfaces caused their subsequent *** the Mg-8%-6%Zn-1.2%Y alloy,the I-phase distributed atα-Mg/β-Li interfaces suppressed the plastic deformation ofα-Mg matrix phase and the tensile strain was dominated by theβ-Li matrix phase,resulting in the disappearance of plastic ***,the plastic strain would preferentially concentrate at I-phase/β-Li interfaces and subsequently induced the cracking of I-phase.

关键词： Mg-li alloys Microstructure Plastic deformation Basal slip Cracking