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连接温度对W/Ni/Kovar真空扩散连接接头界面结构及结合强度的影响

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材料导报 2024年第4期38卷 139-144页

作者：仵金玲刘思雨张彪魏智磊史忠旗西安交通大学金属材料强度国家重点实验室西安710049

以Ni箔为中间层材料,采用真空扩散连接方法进行W与Kovar合金的连接,研究了连接温度对W/Ni/Kovar接头界面结构和剪切强度的影响。结果表明:在520~1000℃范围内,利用真空扩散连接工艺均可成功制备出W/Ni/Kovar接头样品。随着连接温度的升... 详细信息

以Ni箔为中间层材料,采用真空扩散连接方法进行W与Kovar合金的连接,研究了连接温度对W/Ni/Kovar接头界面结构和剪切强度的影响。结果表明:在520~1000℃范围内,利用真空扩散连接工艺均可成功制备出W/Ni/Kovar接头样品。随着连接温度的升高,Kovar/Ni界面与Ni/W界面的扩散层厚度逐渐增加,而接头剪切强度呈先上升后下降的趋势。当连接温度为800℃时,样品的接头剪切强度高达182 MPa,此时主要发生W块体的剪切断裂。

关键词：真空扩散焊剪切强度钨 Kovar合金中间层

Preparation of SiC coated graphite composite powders by nitriding combustion synthesis

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Journal of Advanced Ceramics 2023年第10期12卷 1930-1945页

作者： Biao Zhang Wenqi Xie Huaizhi Lin zhilei wei Zhichao Xiao Kai He Zhongqi Shi State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China China Nuclear Power Engineering Co. Ltd.Beijing 100840China

Ceramic-coated graphite powders are considered as effective raw materials to fabricate three-dimensional continuous ceramic skeleton-reinforced graphite matrix composites which can overcome their inherent poor densification and improve their mechanical and antioxidation ***,the morphology and thickness regulation of ceramic coatings on graphite particles are still a great ***,SiC-coated graphite(graphite@SiC)powders were prepared by nitriding combustion synthesis using Si and graphited mesocarbon microbead(MCMB)as raw powders with polytetrafluoroethylene(PTFE)as a *** effects of the PTFE content and the Si/MCMB molar ratio on the phase composition and coating morphology were *** phase transition and microstructure evolution of a combustion synthesis(CS)process were revealed by a gas-released quenching *** the Si/MCMB molar ratio was 1:3 and the PTFE content was 10 wt%,the thickness of the SiC coating synthesized under 2 MPa N_(2)reached 1.14μ*** corresponding sintered graphite@SiC composite had relative density of 99.2%and flexural strength of 231 MPa,accompanied by a significant improvement in high-temperature antioxidation *** as-synthesized graphite@SiC powders with good sinterability and antioxidation properties show great promise for applications in the nuclear industry and other extreme fields.

关键词： SiC-coated graphite powders nitriding combustion synthesis(CS) antioxidation properties

Synthesis of nearly spherical AlN particles by an in-situ nitriding combustion route

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Journal of Advanced Ceramics 2021年第2期10卷 291-300页

作者： zhilei wei Kang Li Bangzhi Ge Chaowei Guo Hongyan Xia Yajie Guo Zhongqi Shi State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an710049China Engineering Research Center of Transportation Materials of Ministry of Education School of Materials Science and EngineeringChang’an UniversityXi’an710064China

Spherical AlN powders with micrometer size have attracted great attention owing to their good fluidity and dispersity. However, the industrial preparation methods usually require high temperature and long soaking time, which lead to the high cost and limit the wide application of the products. Herein, nearly spherical AlN particles with the average size of 2.5 μm were successfully synthesized via an in-situ combustion synthesis method. The effect of N_(2) pressure, NH_(4)Cl content, and Al particle size on the combustion reaction procedure, phase composition, and microstructure of the products was systematically investigated. The results showed that the decreased N_(2) pressure, increased NH_(4)Cl content, and Al particle size led to the decreasing of combustion temperature and speed, which further affected the morphology of the products. As a result, low N_(2) pressure(0.2 MPa), a small amount of NH4Cl(0.5 wt%), and fine Al particles(~2.5 μm) contributed to a moderate combustion temperature and facilitated the formation of nearly spherical AlN particles. In addition, based on the gas-releasing assisted quenching experiments and thermo-kinetic analysis, a two-step growth mechanism for the nearly spherical AlN particles was rationally proposed. The present method shows the advantages of low cost and high efficiency for preparing nearly spherical AlN particles, which can be used as raw materials for electronic substrates and fillers for packaging materials.

关键词： combustion synthesis AlN microstructure growth mechanism

Preparation of unidirectional porous AlN ceramics via the combination of freeze casting and combustion synthesis

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Journal of Materials Science & Technology 2022年第5期100卷 161-168页

作者： zhilei wei Zhejian Zhang Xiaoyu Zhang Zhiyuan Li Tao Li Jiabin Hu Shunjian Xu Zhongqi Shi State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an 710049China School of Mechanical and Electrical Engineering Xinyu UniversityXinyu 338000China

Unidirectional porous AlN ceramics(UP-AlNs)have attracted great attention for their wide applications in catalyst supports,filters and composite ***,traditional fabrication processes usually require high temperature and long production ***,UP-AlNs were successfully fabricated via the combination of tertiary butyl alcohol(TBA)-based freeze casting and combustion synthesis route using Al and AlN powders as raw *** microstructure,open porosity,thermal conductivity and compressive strength of UP-AlNs can be manipulated by synergistically regulating the AlN diluent content and Al/AlN solid loading of the freezing *** optimal UP-AlNs exhibited controllable structure wavelength(λ)and open porosity in a wide range of 21.1-47.1μm and 54.2%-86.0%,*** addition,the corresponding products also possessed anisotropic thermal conductivity and compressive *** novel route for the fabrication of UP-AlNs has the advantages of low cost,energy-saving and high efficiency,which shows significant promise for industrial applications.

关键词： AlN Freeze casting Combustion synthesis Thermal conductivity Compressive strength

Continuous SiC skeleton reinforced highly oriented graphite flake composites with high strength and specific thermal conductivity

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Journal of Advanced Ceramics 2022年第3期11卷 403-413页

作者： Xiaoyu ZHANG Wenqi XIE Lan SUN zhilei wei Zhejian ZHANG Yuanyuan ZHU Jiabin HU Shenghe WANG Zhongqi SHI State Key Laboratory for Mechanical Behavior of Materials Xi’an Jiaotong UniversityXi’an710049China State Grid Anhui Electric Power Co. Ltd.Hefei230061China

Highly oriented graphite-based composites have attracted great attention because of their high thermal conductivity(TC),but the low mechanical properties caused by the inhomogeneous distribution and discontinuity of reinforcements restrict the wide ***,continuous SiC ceramic skeleton reinforced highly oriented graphite flake(SiC/GF)composites were successfully prepared by combining vacuum filtration and spark plasma *** effect of SiC concentration on the microstructure,flexural strength,and thermophysical properties of the composites was *** GF grains in the composites exhibited high orientation with a Lotgering factor of>88%when the SiC concentration was≤30 wt%,and the SiC skeleton became continuous with the SiC concentration reaching 20 wt%.The formation of continuous SiC skeleton improved the flexural strength of the composites effectively while keeping the TC in a high ***,the composites with 30 wt%SiC exhibited the flexural strength up to 105 MPa,and the specific TC reaching 0.118 W·m^(2)·K^(−1)·*** composites with excellent flexural strength and thermophysical properties showed significant promise for thermal management applications.

关键词： ceramics composite materials high orientation flexural strength heat conduction

A low-frequency and broadband wave-insulating vibration isolator based on plate-shaped metastructures

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Applied Mathematics and Mechanics(English Edition) 2024年第7期45卷 1171-1188页

作者： wei wei Feng GUAN Xin FANG College of Intelligent Science National University of Defense TechnologyChangsha410073China Naval Research Academy Beijing100161China

A metamaterial vibration isolator,termed as wave-insulating isolator,is proposed,which preserves enough load-bearing capability and offers ultra-low and broad bandgaps for greatly enhanced wave *** consists of plate-shaped metacells,whose symmetric and antisymmetric local resonant modes offer several low and broad mode bandgaps although the complete bandgap remains high and *** bandgap mechanisms,vibration isolation properties,effects of key parameters,and robustness to complex conditions are *** experimentally demonstrated,the wave-insulating isolator can improve the vibration insulation in the ranges of[50 Hz,180 Hz]and[260 Hz,400 Hz]by 15 dB and 25 dB,respectively,in contrast to the conventional isolator with the same first resonant frequency.

关键词： metamaterial and metastructure vibration isolation bandgap wave insulation plate

The lithology and composition of lunar mantle modifi ed by ilmenite bearing cumulate: A thermodynamic model

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Acta Geochimica 2024年第05期43卷 856-875页

作者： wei Huang wei Du State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of Sciences University of Chinese Academy of Sciences Center for Excellence in Comparative Planetology Chinese Academy of Sciences

Due to their high density,the ilmenite-bearing cumulates (IBC)(with or without KREEP) formed during the late-stage lunar magma ocean solidifi cation are thought to sink into the underlying lunar mantle and trigger lunar mantle *** evidence implied that IBC may descend deep inside the Moon and remain as a partially molten layer at the core-mantle boundary (CMB).However,partial melting may have occurred on the mixed mantle cumulates during the sinking of IBC/KREEP and the silicate melt may be positively buoyant,thus preventing the IBC/KREEP layer from sinking to the ***,we perform thermodynamic simulation on the stability of lunar mantle cumulates at diff erent depths mixed with diff erent amounts of IBC/KREEP from an updated LMO *** modeling results suggest that the sinking of IBC/KREEP will cause at least 5 wt%partial melting in the shallow (～120 km) and a much larger degree of partial melting in the deep lunar mantle (～420 km).Due to the density contrast with the surrounding mantle,IBC/KREEP-bearing melts could potentially decouple under certain *** modifi ed lunar mantle by sinking of IBC/KREEP can better explain the formation of diff erent kinds of lunar basaltic magma than the primary lunar mantle formed through diff erentiation of lunar magma *** of IBC/KREEP back into the lunar mantle may introduce plagioclase,clinopyroxene,garnet,and incompatible radioactive elements into the deep lunar mantle,which will further aff ect the thermal and chemical evolution of the lunar interior.

关键词： Ilmenite-bearing cumulate KREEP Lunar mantle overturn Partial melting pMELTS

Task-specific Part Discovery for Fine-grained Few-shot Classification

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Machine Intelligence Research 2024年第5期21卷 954-965页

作者： Yongxian wei Xiu-Shen wei School of Computer Science and Technology Nanjing University of Science and TechnologyNanjing210094China

Localizing discriminative object parts(e.g.,bird head)is crucial for fine-grained classification tasks,especially for the more challenging fine-grained few-shot *** work always relies on the learned object parts in a unified manner,where they attend the same object parts(even with common attention weights)for different few-shot episodic *** this paper,we propose that it should adaptively capture the task-specific object parts that require attention for each few-shot task,since the parts that can distinguish different tasks are naturally *** for a few-shot task,after obtaining part-level deep features,we learn a task-specific part-based dictionary for both aligning and reweighting part features in an ***,part-level categorical prototypes are generated based on the part features of support data,which are later employed by calculating distances to classify query data for *** retain the discriminative ability of the part-level representations(i.e.,part features and part prototypes),we design an optimal transport solution that also utilizes query data in a transductive way to optimize the aforementioned distance calculation for the final *** experiments on five fine-grained benchmarks show the superiority of our method,especially for the 1-shot setting,gaining 0.12%,8.56%and 5.87%improvements over state-of-the-art methods on CUB,Stanford Dogs,and Stanford Cars,respectively.

关键词： Fine-grained image recognition few-shot learning transductive learning visual dictionary part feature discovery

Humic acid-mediated transport of a typical soil passivation remediation product(chloropyromorphite)in saturated porous media

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Journal of Environmental Sciences 2024年第7期141卷 51-62页

作者： Xinying Li Mengjia Zhang Siyuan Li wei wei School of Environment Jiangsu Engineering Lab of Water and Soil Eco-remediationJiangsu Province Engineering Research Center of Environmental Risk Prevention and Emergency Response TechnologyNanjing Normal UniversityNanjing 210023China Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application Nanjing 210023China

Conversion of labile Pb species into chloropyromorphite(CPY)using phosphorus-bearing amendments was considered to be an ideal strategy in soil passivation ***,the fate and transport of CPY in the soil are poorly *** study aims to fill the knowledge gap by evaluating the fate and transport of CPY under environmentally relevant conditions of humic acid(HA),pH,electrolyte concentration,and species through the saturated sandy *** showed that bare CPY colloids are basically immobile in sandy porous media while the co-existence of HA made the transport of CPY improved by30%-93.5%.Facilitated transport of CPY was attributed to the increased stability of CPY and the repulsive interaction between CPY particles and sands due to HA *** mobility of CPY was also increased with increasing pH from 5.0 to *** the pH was 9 with a10 mmol/L NaCl background solution,the stronger energy barrier between CPY and sand led to enhanced transport *** divalent Ca^(2+)had a more dramatic effect than monovalent Na^(+)on the aggregation and sedimentation of CPY colloids due to its effectivescreening of the surface charge of CPY and bridging interaction with CPY ***-LandauVerwey-Overbeek theory and attachment efficiency calculation indicated that high energy barriers were responsible for the high mobility of CPY colloids,while the retention of CPY in sands was mainly caused by secondary energy minimum and physically *** findings of this work can help to evaluate the fate of soil passivation remediation products in natural water and soil.

关键词： Chloropyromorphite DLVO theory Stability Saturated porous medium Transport