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Improving repair performance for damaged C/C composites via heat-treatment temperature optimization and surface pretreatment

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Journal of Materials Science & Technology 2024年第16期183卷 120-132页

作者： Weiyan Wang Qiangang Fu Dou Hu tianyu liu Shaanxi Province Key Laboratory of Fiber Reinforced Light Composite Materials State Key Laboratory of Solidification ProcessNorthwestern Polytechnical UniversityXi’an 710072China

A Ni-based solder BNi-5 was adopted as the repair agent to repair the prefabricated defects on the car-bon/carbon(C/C)*** effects of different heat-treatment(HT)temperatures and pre-oxidation on the chemical composition,microstructure,and mechanical behavior of the repaired C/C composites were investigated,and the repair mechanism was studied by finite element analysis *** repair agent and C/C composites were tightly bonded through mechanical interlocking and chemical reactions,and the flexural properties of the damaged C/C composites were significantly improved after *** products at the interface formed a gradient distribution structure of the thermal expansion coefficient when the HT temperature was 1300°C,which is beneficial to relieve the residual thermal stress at the ***,the porosity of the surface of the C/C composites was higher after pre-oxidation,which led to more diffusion channels for the repair agent and enhanced the interface bonding *** flexural strength was the highest with a recovery rate of 85.2%when the C/C composites were pre-oxidized at 600°C and the HT temperature was 1300°*** work provides a strategy for the engineering application of the damage repair of C/C composites.

关键词： Carbon/carbon composites Damage repair BNi-5 Flexural strength

Addressing the Achilles'heel of pseudocapacitive materials:Long-term stability

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InfoMat 2020年第5期2卷 807-842页

作者： tianyu liu Yat Li Department of Chemistry Virginia Polytechnic Institute and State UniversityBlacksburgVirginia Department of Chemistry and Biochemistry University of CaliforniaSanta CruzCalifornia

Electrode materials with high energy densities and long-lasting performances are crucial to durable and reliable electrochemical energy storage devices for modern information technologies(eg,Internet of things).In terms of supercapacitors,their low energy densities could be enhanced by using pseudocapacitive electrodes,but meanwhile,their ultralong lifetimes are compromised by the limited chargedischarge cycling stabilities of pseudocapacitive *** review article discusses on the cycling instability issues of five common pseudocapacitive materials:conjugated polymers(or conducting polymers),metal oxides,metal nitrides,metal carbides,and metal ***,the article includes the fundamentals of the failure modes of these materials,as well as thoroughly surveys the design rationales and technical details of the cycling-stability-boosting tactics for pseudocapacitive materials that reported in the ***,promising opportunities,future challenges,and possible solutions associated with pseudocapacitive materials are discussed.

关键词： conjugated polymer cycling stability metal carbide metal nitride metal oxide metal sulfide pseudocapacitive

A Review on Nano-/Microstructured Materials Constructed by Electrochemical Technologies for Supercapacitors

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Nano-Micro Letters 2020年第9期12卷 147-202页

作者： Huizhen Lv Qing Pan Yu Song Xiao‑Xia liu tianyu liu Department of Chemistry Northeastern UniversityShenyang 110819People’s Republic of China Department of Chemistry Virginia Polytechnic Institute and State UniversityBlacksburgVA 24061USA

The article reviews the recent progress of electrochemical techniques on synthesizing nano-/microstructures as supercapacitor *** a history of more than a century,electrochemical techniques have evolved from metal plating since their inception to versatile synthesis tools for electrochemically active materials of diverse morphologies,compositions,and *** review begins with tutorials on the operating mechanisms of five commonly used electrochemical techniques,including cyclic voltammetry,potentiostatic deposition,galvanostatic deposition,pulse deposition,and electrophoretic deposition,followed by thorough surveys of the nano-/microstructured materials synthesized ***,representative synthesis mechanisms and the state-of-the-art electrochemical performances of exfoliated graphene,conducting polymers,metal oxides,metal sulfides,and their composites are *** article concludes with summaries of the unique merits,potential challenges,and associated opportunities of electrochemical synthesis techniques for electrode materials in supercapacitors.

关键词： Nanostructure Microstructure Electrochemical Synthesis Supercapacitor

Well-dispersed ultrafine nitrogen-doped TiO_2 with polyvinylpyrrolidone(PVP) acted as N-source and stabilizer for water splitting

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Journal of Energy Chemistry 2016年第1期25卷 1-9页

作者： tianyu liu Wei Chen Xiaoheng liu Junwu Zhu Lude Lu Key Laboratory for Soft Chemistry and Functional Materials Nanjing University of Science and Technology Ministry of Education

In this paper, ultrafine nitrogen-doped TiO2 photocatalyst with enhanced photocatalytic water-splitting properties was successfully fabricated via a solvothermal method. Herein, polyvinylpyrrolidone（PVP） was used as both nitrogen source and stabilizer. The enhancement in water-splitting process can be attributed to the doping of element nitrogen, which could supply an intermediate energy level and promote the separation of photo-excited holes and electrons. Moreover, this paper provides a new application of high-molecular polymer to synthesize solar-driven water-splitting photocatalysts.

关键词： N-doped TiO2 Polyvinylpyrrolidone(PVP) Solar-light driven Water splitting

Composition formulas of Ti alloys derived by interpreting Ti-6Al-4V

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Science China(Technological Sciences) 2021年第8期64卷 1732-1740页

作者： liu tianyu ZHANG Shuang WANG Qing MIN XiaoHua DONG Chuang Key Laboratory for Materials Modification by Laser Ion and Electron BeamsDalian University of TechnologyMinistry of EducationDalian116024China School of Materials Science and Engineering Dalian Jiaotong UniversityDalian116028China

Titanium alloys are composed ofαandβphases and are classified as nearα,dual-phaseα+β,andβ*** study attempts to derive their general composition formulas within the cluster-plus-glue-atom model by interpreting Ti-6A1-4V and other popular dual-phaseα+βTi alloy s with well-established chemical *** model identifiedαmolecule-like structural unit that covers onlyαnearest-neighbor cluster along withαfew next-neighbor glue atoms,which can be represented as"[cluster](glue atoms)x".The structural units of theαandβphases in Ti-6Al-4V,α-[Al-Ti_(12)](AlTi_(2)),andβ-[Al-Ti_(14)](V2Ti),were derived first and were in an unusual unit ratio of about 2.33:*** obtain an alloy composition formula that satisfied this unit ratio,the two clusters were treated as hard spheres of different radii and packed according to the clusterplusglueatom *** calculations determined that the Ti-6A1-4V alloy unit is composed of 12α-[Al-Ti_(12)](AlTi_(2))and 5β-[Al-Ti_(14)](V2Ti)units(Ti-6.05A1-3.94V wt.%),with the fractional volume of theβphase being 32.5 vol.%,which is in agreement with experimental ***,we describe how the chemical formulas of theαand p phases explain the high temperature near-a alloys(such as Ti-1100,[Al-(Ti_(0.97)Zr_(0.03))_(12)](Al_(0.67)Si_(0.12)Sn_(0.18)Mo_(0.03))_(1.01)Ti_(1.99))and high-strengthβ-Ti alloys(such as Ti-5553,[Al-Ti_(14)](Al_(0.24)Fe_(0.03)Cr_(0.20)-Mo_(0.18)V0.35)_(2.45)Ti_(0.55)),respectively.

关键词： Ti-6Al-4V titanium alloys chemical formula cluster-plus-glue-atom model cluster-resonance model

Design of Ultra-Strong As-Cast Titanium Alloy at 600 degree celsius by Using Cluster Formula

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ACTA METALLURGICA SINICA-ENGLISH LETTERS 2024年第12期37卷 2068-2082页

作者： Zhu, Zhihao Wang, Cenyang liu, tianyu Zhang, Shuang Dong, Chuang Dalian Univ Technol Key Lab Mat Modificat Laser Ion & Electron Beams Dalian 116024 Peoples R China Dalian Univ Technol Sch Mat Sci & Engn Dalian 116024 Peoples R China Shenyang Res Inst Foundry Co Ltd Natl Key Lab Adv Casting Technol Shenyang 110022 Peoples R China Dalian Jiaotong Univ Sch Mat Sci & Engn Dalian 116028 Peoples R China

A Ti-5.4Al-6.4Zr-6.2Sn-0.4Mo-1.6W-0.4Nb-3.2Ta-0.5Si alloy is designed following cluster formula approach that achieves a strength level of 1 GPa at 600 degree celsius in the as-cast state, superior to any existing high-temperature Ti alloys. Its composition is formulated by 17 basic units, alpha-{[Al-Ti12](AlTi2)}12 + beta-{[Al-Ti12Zr2](Mo0.125Nb0.125Ta0.5W0.25Sn1.5Si0.5)}5, each unit covering a nearest-neighbor cluster plus a few next-neighbor glue atoms. This design is on the basis of the composition formula of Ti65 alloy, with an enhanced beta stability via more Zr, Mo, Nb, Ta, W, Sn, and Si co-alloying. Upon copper-mold pour casting, this alloy shows a good microstructure stability. In tensile testing below at 650 degree celsius, its alpha plates thickness is nearly at the same level of 0.2 mu m, which is much smaller than 0.7-0.8 mu m of Ti65 at the same condition. The changes in volume fraction of beta phase are increased by 86%, much less than by 105% in Ti65. Its room-temperature strength reaches the ultra-high-strength level, with an ultimate tensile strength of 1328 MPa and a yield strength of 1117 MPa, with a moderate elongation of 3.8%. At 600 degree celsius, its ultimate tensile strength of 1017 MPa and yield strength of 936 MPa are superior to those of any existing high-temperature Ti alloys, with an elongation of 7.2%. At 650 degree celsius, its ultimate tensile strength of 848 MPa still maintains a high level.

关键词： High-temperature Ti alloys Cluster formula Microstructure Mechanical properties

Fast CU Partition for VVC Using Texture Complexity Classification Convolutional Neural Network

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Computers, Materials & Continua 2022年第11期73卷 3545-3556页

作者： Yue Zhang Pengyu liu Xiaowei Jia Shanji Chen tianyu liu Chang liu The Information Department Beijing University of TechnologyBeijing100124China School of Physics and Electronic Information Engineering Qinghai Minzu UniversityXining810000China Advanced Information Network Beijing Laboratory Beijing100124China Computational Intelligence and Intelligent Systems Beijing Key Laboratory Beijing100124China Department of Computer Science University of PittsburghPittsburgh15260USA

Versatile video coding(H.266/VVC),which was newly released by the Joint Video Exploration Team(JVET),introduces quad-tree plus multitype tree(QTMT)partition structure on the basis of quad-tree(QT)partition structure in High Efficiency Video Coding(H.265/HEVC).More complicated coding unit(CU)partitioning processes in H.266/VVC significantly improve video compression efficiency,but greatly increase the computational complexity *** ultra-high encoding complexity has obstructed its real-time *** order to solve this problem,a CU partition algorithm using convolutional neural network(CNN)is proposed in this paper to speed up the H.266/VVC CU partition ***,64×64 CU is divided into smooth texture CU,mildly complex texture CU and complex texture CU according to the CU texture ***,CU texture complexity classification convolutional neural network(CUTCC-CNN)is proposed to classify ***,according to the classification results,the encoder is guided to skip different RDO search *** optimal CU partition results will be *** results show that the proposed method reduces the average coding time by 32.2%with only 0.55%BD-BR loss compared with VTM 10.2.

关键词： Versatile video coding(VVC) coding unit partition convolutional neural network(CNN)

Progress on the antiferromagnetic topological insulator MnBi2Te4

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National Science Review 2024年第2期11卷 33-49页

作者： Shuai Li tianyu liu Chang liu Yayu Wang Hai-Zhou Lu X.C.Xie Department of Physics Harbin Institute of Technology Shenzhen Institute for Quantum Science and Engineering and Department of Physics Southern University of Science and Technology(SUSTech) Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area(Guangdong) Shenzhen Key Laboratory of Quantum Science and Engineering International Quantum Academy Beijing Academy of Quantum Information Sciences Beijing Key Laboratory of Optoelectronic Functional Materials&Micro-Nano Devices Department of Physics Renmin University of China State Key Laboratory of Low Dimensional Quantum Physics Department of PhysicsTsinghua University Frontier Science Center for Quantum Information Hefei National Laboratory International Center for Quantum Materials School of Physics Peking University Institute for Nanoelectronic Devices and Quantum Computing Fudan University

Topological materials, which feature robust surface and/or edge states, have now been a research focus in condensed maTher physics. They represent a new class of materials exhibiting nontrivial topological phases,and provide a platform for exploring exotic transport phenomena, such as the quantum anomalous Hall effect and the quantum spin Hall effect. Recently, magnetic topological materials have attracted considerable interests due to the possibility to study the interplay between topological and magnetic *** particular, the quantum anomalous Hall and axion insulator phases can be realized in topological insulators with magnetic order. MnBi2Te4, as the first intrinsic antiferromagnetic topological insulator discovered, allows the examination of existing theoretical predictions; it has been extensively studied, and many new discoveries have been made. Here we review the progress made on MnBi2Te4from both experimental and theoretical aspects. The bulk crystal and magnetic structures are surveyed first, followed by a review of theoretical calculations and experimental probes on the band structure and surface states, and a discussion of various exotic phases that can be realized in MnBi2Te4. The properties of MnBi2Te4thin films and the corresponding transport studies are then reviewed, with an emphasis on the edge state transport. Possible future research directions in this field are also discussed.

关键词： MnBi2Te4 magnetic topological insulator antiferromagnetic quantum anomalous Hall effect axion insulator

Ultrafast investigation of room temperature valley polarization in“optical bilayer”WS_(2)

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Science China(Technological Sciences) 2024年第1期67卷 91-97页

作者： ZHAO LeYi WANG Hai liu tianyu LI FangFei ZHOU Qiang WANG HaiYu Synergetic Extreme Condition High-Pressure Science Center State Key Laboratory of Superhard MaterialsCollege of PhysicsJilin UniversityChangchun 130012China State Key Laboratory of Integrated Optoelectronics College of Electronic Science and EngineeringJilin UniversityChangchun 130012China

Monolayer transition metal dichalcogenides(TMDCs)have become a promising platform in valleytronics due to possessing the regulatable valley degrees of ***,as a result of the rapid intervalley scattering,it is difficult to measure the PL valley polarization of monolayer TMDCs at room temperature,which limits their application in valleytronics ***,we report a room temperature photoluminescence(PL)valley polarization up to 3.73%in an“optical bilayer”WS_(2)formed by transferring monolayer WS_(2)onto flat Ag ***,in the transient absorption(TA)measurements,a remarkably long valley depolarization lifetime is ***,we demonstrate the valley properties of such“optical bilayer”WS_(2)resemble actual bilayer WS_(2),in which the robust valley polarization can be attributed to the phonons depletion effect and the blocked interlayer hopping *** peculiar valley features in“optical bilayer”WS_(2)provide a particularly simple method to enhance valley control at room temperature.

关键词： valleytronics optical bilayer transient absorption tungsten disulfide