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Equiatomic 9-cation high-entropy carbide ceramics of the IVB,VB,and VIB groups and thermodynamic analysis of the sintering process

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Journal of Advanced Ceramics 2022年第7期11卷 1082-1092页

作者： Yuan QIN ji-xuan liu Yongcheng LIANG Guo-Jun ZHANG State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringDonghua UniversityShanghai 201620China Institute of Functional Materials Donghua UniversityShanghai 201620China College of Science Donghua UniversityShanghai 201620China

The preparation of high-entropy(HE)ceramics with designed composition is essential for verifying the formability models and evaluating the properties of the ceramics.However,inevitable oxygen contamination in non-oxide ceramics will result in the formation of metal oxide impurity phases remaining in the specimen or even escaping from the specimen during the sintering process,making the elemental compositions of the HE phase deviated from the designed ones.In this work,the preparation and thermodynamic analysis during the processing of equiatomic 9-cation HE carbide(HEC9)ceramics of the IVB,VB,and VIB groups were studied focusing on the removing of the inevitable oxygen impurity existed in the starting carbide powders and the oxygen contamination during the powder mixing processing.The results demonstrate that densification by spark plasma sintering(SPS)by directly using the mixed powders of the corresponding single-component carbides will inhibit the oxygen-removing carbothermal reduction reactions,and most of the oxide impurities will remain in the sample as(Zr,Hf)O_(2)phase.Pretreatment of the mixed powders at high temperatures in vacuum will remove most part of the oxygen impurity but result in a remarkable escape of gaseous Cr owing to the oxygen-removing reaction between Cr_(3)C_(2)and various oxide impurities.It is found that graphite addition enhances the oxygen-removing effect and simultaneously prevents the escape of gaseous Cr.On the other hand,although WC,VC,and Mo2C can also act as oxygen-removing agents,there is no metal-containing gaseous substance formation in the temperature range of this study.By using the heat-treated powders with added graphite,equiatomic HEC9 ceramics were successfully prepared by SPS.

关键词： high-entropy(HE)carbide oxygen impurity carbothermal reduction reaction phase composition thermodynamic analysi

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Fast grain growth phenomenon in high-entropy ceramics:A case study in rare-earth hexaaluminates

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Journal of Advanced Ceramics 2023年第1期12卷 111-121页

作者： Lin ZHOU ji-xuan liu Tian-Zhe TU Yue WU Guo-Jun ZHANG State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringInstitute of Functional MaterialsDonghua UniversityShanghai 201620China

It is generally reported that the grain growth in high-entropy ceramics at high temperatures is relatively slower than that in the corresponding single-component ceramics owing to the so-called sluggish diffusion effect.In this study,we report a fast grain growth phenomenon in the high-entropy ceramics(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))MgAl_(11)O_(19)(HEMA)prepared by a conventional solid-state reaction method.The results demonstrate that the grain sizes of the as-sintered HEMA ceramics are larger than those of the corresponding five single-component ceramics prepared by the same pressureless sintering process,and the grain growth rate of HEMA ceramics is obviously higher than those of the five single-component ceramics during the subsequent heat treatment.Such fast grain growth phenomenon indicates that the sluggish diffusion effect cannot dominate the grain growth behavior of the current high-entropy ceramics.The X-ray photoelectron spectroscopy(XPS)analysis reveals that there are more oxygen vacancies(OV)in the high-entropy ceramics than those in the single-component ceramics owing to the variable valance states of Eu ion.The high-temperature electrical conductivities of the HEMA ceramics support this analysis.It is considered that the high concentration of OV and its high mobility in HEMA ceramics contribute to the accelerated migration and diffusion of cations and consequently increase the grain growth rate.Based on this study,it is believed that multiple intrinsic factors for the high-entropy ceramic system will simultaneously determine the grain growth behavior at high temperatures.

关键词： high-entropy ceramics rare-earth hexaaluminate fast grain growth electrical conductivity

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Synergistic effects of high-entropy engineering and particulate toughening on the properties of rare-earth aluminate-based ceramic composites

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Journal of Advanced Ceramics 2023年第4期12卷 861-872页

作者： Tian-Zhe Tu ji-xuan liu Yue Wu Lin Zhou Yongcheng Liang Guo-Jun Zhang State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringCollege of ScienceInstitute of Functional MaterialsDonghua UniversityShanghai 201620China

Rare-earth aluminates(REAIOs)are potential thermal barrier coating(TBC)materials,but the relatively high thermal conductivity(ko,~13.6 W·m^(-1)·K^(-1))and low fracture toughness(K_(1c),-1.9 MPa·m^(1/2))limit their application.This work proposed a strategy to improve their properties through the synergistic effects of high-entropy engineering and particulate toughening.High-entropy(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2)AlO_(3))(HEAO)-based particulate composites with different contents of high-entropy(La_(0.2)Nd_(0.2)Sm_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)O_(7)(HEZO)were designed and successfully prepared by solid-state sintering.The high-entropy feature of both the matrix and secondary phases causes the strong phonon scattering and the incorporation of the HEZO secondary phase,remarkedly inhibiting the grain growth of the HEAO phase.As a result,HEAO-xHEZO(x=0,5%,10%,25%,and 50%in volume)ceramic composites show low thermal conductivity and high fracture toughness.Compared to the most commonly applied TBC material-yttria stabilized-zirconia(YSZ),the HEAO-25%HEZO particulate composite has a lower thermal conductivity of 0.96-1.17 W·m^(-1)·K^(-1)(298-1273 K),enhanced fracture toughness of 3.94±0.35 MPa-m,and comparable linear coefficient of thermal expansion(CTE)of 10.5×10^(-6)K^(-1).It is believed that the proposed strategy should be revelatory for the design of new coating materials including TBCs and environmental barrier coatings(EBCs).

关键词： high-entropy particulate composites thermal barrier coating(TBC) thermal properties mechanical properties fine grains

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Effect of native carbon vacancies on evolution of defects in ZrC_(1-x)under He ion irradiation and annealing

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Journal of Materials Science & Technology 2022年第24期119卷 87-97页

作者： Weichao Bao Xin-Gang Wang Ying Lu ji-xuan liu Shikuan Sun Guo-Jun Zhang Fangfang Xu State Key Laboratory of High Performance Ceramics and Superfine Microstructure Shanghai Institute of CeramicsShanghai 200050China State Key Laboratory for Modification of Chemical Fibers and Polymer Materials Institute of Functional MaterialsDonghua UniversityShanghai 201620China School of Material Science and Energy Engineering Foshan UniversityFoshan 528000China

The dynamic study of radiation-induced defects with annealing is critical for the material design for nextgeneration nuclear energy systems.The native vacancy could affect the development of defects,which lacks study.In the present work,the as-hot pressed ZrC_(1-x)(x=0,0.15,0.3)ceramics which comprised crystallites of a few microns in size with different amounts of carbon vacancies were irradiated by 540 ke V He^(2+)ions at room temperature with a fluence of 1×10^(17)/cm^(2).The radiation-induced lattice expansion was found to be a common phenomenon in a sequence of ZrC_(0.85)≥ZrC_(1.0)>ZrC_(0.7).Both X-ray and electron diffractions confirmed maintenance of structural integrity without amorphization after irradiation.Inside the irradiated region,only“black-dot”type defects,i.e.,clusters of point defects were observed while no helium-induced cavities,cracks,or extended dislocations were detected.The as-irradiated ZrC_(1-x)were then annealed at different high temperatures.Upon annealing at 800℃,very tiny helium-induced cavities were found to be generated and the crystal lattice recovered to a great extent,especially for the sub-stoichiometric samples.While annealed at 1500℃,all the samples almost fully recovered the crystal lattices close to those of as-hot pressed ones.Meanwhile,large cavities and extended dislocations were generated.With increasing amount of native carbon vacancies,the size of cavities increased while the length and density of extended dislocations decreased.Inverse changes of lattice parameters during irradiation and annealing processes have been interpreted by the kinetics of defects.Finally,the correlation between native vacancies and damage behavior is discussed.

关键词： Native carbon vacancies Zirconium carbide He ions irradiation Helium bubbles Dislocations

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Advances in ultra-high temperature ceramics,composites,and coatings

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Journal of Advanced Ceramics 2022年第1期11卷 1-56页

作者： Dewei NI Yuan CHENG jiaping ZHANG ji-xuan liu ji ZOU Bowen CHEN Haoyang WU Hejun LI Shaoming DONG jiecai HAN Xinghong ZHANG Qiangang FU Guo-Jun ZHANG State Key Laboratory of High Performance Ceramics&Superfine Microstructure Structural Ceramics and Composites Engineering Research CenterShanghai Institute of CeramicsChinese Academy of SciencesShanghai 200050China National Key Laboratory of Science and Technology on Advanced Composites in Special Environments Center for Composite Materials and StructuresHarbin Institute of TechnologyHarbin 150001China Shaanxi Key Laboratory of Fiber Reinforced Light Composite Materials Northwestern Polytechnical UniversityXi’an 710072China State Key Laboratory for Modification of Chemical Fibers and Polymer Materials Institute of Functional MaterialsDonghua UniversityShanghai 201620China State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of TechnologyWuhan 430070China University of Chinese Academy of Sciences Beijing 100049China

Ultra-high temperature ceramics(UHTCs)are generally referred to the carbides,nitrides,and borides of the transition metals,with the Group IVB compounds(Zr&Hf)and TaC as the main focus.The UHTCs are endowed with ultra-high melting points,excellent mechanical properties,and ablation resistance at elevated temperatures.These unique combinations of properties make them promising materials for extremely environmental structural applications in rocket and hypersonic vehicles,particularly nozzles,leading edges,and engine components,etc.In addition to bulk UHTCs,UHTC coatings and fiber reinforced UHTC composites are extensively developed and applied to avoid the intrinsic brittleness and poor thermal shock resistance of bulk ceramics.Recently,high-entropy UHTCs are developed rapidly and attract a lot of attention as an emerging direction for ultra-high temperature materials.This review presents the state of the art of processing approaches,microstructure design and properties of UHTCs from bulk materials to composites and coatings,as well as the future directions.

关键词： ultra-high temperature ceramics(UHTCs) coatings composites high-entropy ultra-high temperature ceramics

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Pushing the limit of thermal conductivity of MAX borides and MABs

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Journal of Materials Science & Technology 2022年第2期97卷 79-88页

作者： Shaohan Li Weiwei Sun Yi Luo jin Yu Litao Sun Bao-Tian Wang ji-xuan liu Guo-Jun Zhang Igor Di Marco School of Materials Science and Engineering Southeast UniversityNanjing 211189China jiangsu Province Key Laboratory of Advanced Metallic Materials Southeast UniversityNanjing 211189China SEU-FEI Nano-Pico Center Key Laboratory of MEMS of Ministry of EducationSoutheast UniversityNanjing 210096China Institute of High Energy Physics Chinese Academy of Sciences(CAS)Beijing 100049China Collaborative Innovation Center of Extreme Optics Shanxi UniversityTaiyuan 030006China State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringInstitute of Functional MaterialsDonghua UniversityShanghai 201620China Asia Pacific Center for Theoretical Physics PohangGyeonbuk 790-784Republic of Korea Department of Physics POSTECHPohangGyeonbuk 790-784Republic of Korea Department of Physics and Astronomy Uppsala UniversityBox 516Uppsala SE-75120Sweden

The emergence of MAX borides as well as MAB phases attracted great attention because of the renewable developments of ternary ceramics and offering great opportunities in potential applications.However,the number of borides remains limited,and further fundamental descriptions and detailed investigations on various properties are still lacking.In this report,we employ an integrated computational scheme that combines density functional theory with the evolutional algorithm to search for the favorable structures of P-and S-glued ternary borides terminated by Nb metal.We discover that the structures of 212-type,as e.g.Nb_(2)PB_(2)and Nb_(2)SB_(2),belong to the P6m2 space group,while those of 211-type,as e.g.Nb_(2)PB and Nb_(2)SB,prefer to crystallize in the P6_(3)/mmc space group,and the corresponding carbides Nb_(2)PC and Nb_(2)SC are also considered for the sake of completeness and comparative analsys.The predicted Nb_(2)PB_(2),Nb_(2)PB,Nb_(2)SB,Nb_(2)PC and Nb_(2)SC are energetically stable,as revealed by the negative formation energies and by the proposed reaction paths with respect to the most competing phases,as well as dynamically stable,as suggested by the non-imaginary phonon spectra.The thermal conductivities of the six materials show unusual behaviors,particularly for the acoustic and optical contributions,and are accompanied by a strong anisotropy.Most importantly,Nb_(2)PB_(2) is found to be an excellent thermal conductor with a total thermal conductivity of~65 W/(m K),while Nb_(2)SC is found to be an ultra-low thermal conductor,with a total thermal conductivity of~5 W/(m K).These values are clearly outside the currently reported range of thermal conductivities,which makes Nb_(2)PB_(2)and Nb_(2)SC extremely interesting for fundamental research as well as prospective applications with the aid of artificial tunings on the almost independent MB block and the A layer.The discovery of these novel materials is expected to contribute substantially to the rapid development of ternary ceramics and to accelerate at

关键词： MAX and MAB phases Density functional theory calculation Structure searching Thermal conductivity

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Reduced He ion irradiation damage in ZrC-based high-entropy ceramics

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Journal of Advanced Ceramics 2023年第5期12卷 916-929页

作者： Xiao-Ting Xin Weichao Bao Xin-Gang Wang Xiao-jie Guo Ying Lu Chenxi Zhu ji-xuan liu Qiang Li Fangfang Xu Guo-Jun Zhang State Key Laboratory of High Performance Ceramics and Superfine Microstructure Shanghai Institute of CeramicsShanghai 200050China bState Key Laboratory for Modification of Chemical Fibers and Polymer Materials Institute of Functional MaterialsDonghua UniversityShanghai 201620China University of Chinese Academy of Sciences Beijing 100049China School of Engineering Westlake UniversityHangzhou 310024China

Excellent irradiation resistance is the basic property of nuclear materials to keep nuclear safety.The high-entropy design has great potential to improve the irradiation resistance of the nuclear materials,which has been proven in alloys.However,whether or not high entropy can also improve the irradiation resistance of ceramics,especially the mechanism therein still needs to be uncovered.In this work,the irradiation and helium(He)behaviors of zirconium carbide(ZrC)-based high-entropy ceramics(HECs),i.e.,(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C,were investigated and compared with those of ZrC under 540 keV He ion irradiation with a dose of 1×10^(17) cm^(−2) at room temperature and subsequent annealing.Both ZrC and(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C maintain lattice integrity after irradiation,while the irradiation-induced lattice expansion is smaller in(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C(0.78%)with highly thermodynamic stability than that in ZrC(0.91%).After annealing at 800℃,ZrC exhibits the residual _(0.2)0%lattice expansion,while(Zr_(0.2)Ti_(0.2)Nb_(0.2)Ta_(0.2)W_(0.2))C shows only 0.10%.Full recovery of the lattice parameter(a)is achieved for both ceramics after annealing at 1500℃.In addition,the high entropy in the meantime brings about the favorable structural evolution phenomena including smaller He bubbles that are evenly distributed without abnormal coarsening or aggregation,segregation,and shorter and sparser dislocation.The excellent irradiation resistance is related to the high-entropy-induced phase stability,sluggish diffusion of defects,and stress dispersion along with the production of vacancies by valence compensation.The present study indicates a high potential of high-entropy carbides in irradiation resistance applications.

关键词： high-entropy carbides zirconium carbide(ZrC) irradiation damage dislocations helium(He)bubbles

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Sol–gel derived porous ultra-high temperature ceramics

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Journal of Advanced Ceramics 2020年第1期9卷 1-16页

作者： Fei LI Xiao HUANG ji-xuan liu Guo-Jun ZHANG State Key Laboratory for Modification of Chemical Fibers and Polymer Materials Institute of Functional MaterialsDonghua UniversityShanghai 201620China Institute for the Conservation of Cultural Heritage Shanghai UniversityShanghai 200444China

Ultra-high temperature ceramics(UHTCs)are considered as a family of nonmetallic and inorganic materials that have melting point over 3000℃.Chemically,nearly all UHTCs are borides,carbides,and nitrides of early transition metals(e.g.,Zr,Hf,Nb,Ta).Within the last two decades,except for the great achievements in the densification,microstructure tailoring,and mechanical property improvements of UHTCs,many methods have been established for the preparation of porous UHTCs,aiming to develop high-temperature resistant,sintering resistant,and lightweight materials that will withstand temperatures as high as 2000℃for long periods of time.Amongst the synthesis methods for porous UHTCs,sol–gel methods enable the preparation of porous UHTCs with pore sizes from 1 to 500μm and porosity within the range of 60%–95%at relatively low temperature.In this article,we review the currently available sol–gel methods for the preparation of porous UHTCs.Templating,foaming,and solvent evaporation methods are described and compared in terms of processing–microstructure relations.The properties and high temperature resistance of sol–gel derived porous UHTCs are discussed.Finally,directions to future investigations on the processing and applications of porous UHTCs are proposed.

关键词： sol–gel ultra-high temperature ceramics porous ceramics processing microstructure

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High-entropy pyrochlores with low thermal conductivity for thermal barrier coating materials

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Journal of Advanced Ceramics 2019年第4期8卷 576-582页

作者： Fei LI Lin ZHOU ji-xuan liu Yongcheng LIANG Guo-Jun ZHANG State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and Engineering Institute of Functional Materials College of ScienceDonghua University

High-entropy pyrochlore-type structures based on rare-earth zirconates are successfully produced by conventional solid-state reaction method. Six rare-earth oxides(La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, and Y2O3) and ZrO2 are used as the raw powders. Five out of the six rare-earth oxides with equimolar ratio and ZrO2 are mixed and sintered at different temperatures for investigating the reaction process. The results demonstrate that the high-entropy pyrochlores(5RE1/5)2 Zr2O7 have been formed after heated at 1000 ℃. The(5RE1/5)2Zr2O7 are highly sintering resistant and possess excellent thermal stability. The thermal conductivities of the(5RE1/5)2Zr2O7 high-entropy ceramics are below 1 W·m–1·K–1 in the temperature range of 300–1200 ℃. The(5RE1/5)2Zr2O7 can be potential thermal barrier coating materials.

关键词： thermal barrier coating(TBC) pyrochlore high-entropy ceramics thermal conductivity

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Mechanical properties of hot-pressed high-entropy diboride-based ceramics

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Journal of Advanced Ceramics 2020年第4期9卷 503-510页

作者： ji-xuan liu Xiao-Qin Shen Yue Wu Fei Li Yongcheng Liang Guo-Jun Zhang State Key Laboratory for Modification of Chemical Fibers and Polymer Materials College of Materials Science and EngineeringCollege of SciencesInstitute of Functional MaterialsDonghua UniversityShanghai201620China

High-entropy ceramics attract more and more attention in recent years.However,mechanical properties especially strength and fracture toughness for high-entropy ceramics and their composites have not been comprehensively reported.In this work,high-entropy(Ti0.2Zr0.2Hf0.2Nb0.2Ta 0.2)B2(HEB)monolithic and its composite containing 20 vol%SiC(HEB–20SiC)are prepared by hot pressing.The addition of SiC not only accelerates the densification process but also refines the microstructure of HEB,resulting in improved mechanical properties.The obtained dense HEB and HEB–20SiC ceramics hot pressed at 1800℃exhibit four-point flexural strength of 339±17 MPa and 447±45 MPa,and fracture toughness of 3.81±0.40 MPa·m1/2 and 4.85±0.33 MPa·m1/2 measured by single-edge notched beam(SENB)technique.Crack deflection and branching by SiC particles is considered to be the main toughening mechanisms for the HEB–20SiC composite.The hardness Hv0.2 of the sintered HEB and HEB–20SiC ceramics is 23.7±0.7 GPa and 24.8±1.2 GPa,respectively.With the increase of indentation load,the hardness of the sintered ceramics decreases rapidly until the load reaches about 49 N,due to the indentation size effect.Based on the current experimental investigation it can be seen that the room temperature bending strength and fracture toughness of the high-entropy diboride ceramics are within ranges commonly observed in structure ceramics.

关键词： high-entropy ceramics high-entropy diboride flexural strength fracture toughness indentation size effect

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