Benefiting from excellent mechanical properties and low density,cellular ceramic structures(CCSs)are competitive candidates as structural components.However,inherent brittleness from strong chemical bonds among atoms ...Benefiting from excellent mechanical properties and low density,cellular ceramic structures(CCSs)are competitive candidates as structural components.However,inherent brittleness from strong chemical bonds among atoms extremely impeded CCSs'application.Natural materials occupied outstanding strength and toughness simultaneously due to the dual-phase interpenetrated structure.Inspired by natural materials,it was proposed to fabricate coating covered and fulfilled polyurea/CCS interpenetrated composites(C/CCSs and B/CCSs)to circumvent the brittleness of 3D-printed Al_(2)O_(3)CCSs.It was demonstrated that polyurea coating had less effect on the compressive strength of C/CCSs but tremendously improved their energy-absorbing ability.The energy-absorbing ability of C/CCSs was improved from26.48-52.57 kJ·m^(-3)of CCSs to 1.04-1.89 MJ·m^(-3)because of the extended plateau stage.Furthermore,compressive strength and energy-absorbing ability of B/CCSs were strengthened to 1.33-1.36 and 2.84-4.61 times of C/CCSs,respectively.Besides,failure mode of C/CCSs changed from localized deformation to fracturing entirely with the increase in relative density of CCSs inside,which was the same as that of CCSs.However,with the help of polyurea coating,C/CCSs were still intact at strains up to60%,which would neve r fail catastrophically as CCSs at low strains.B/CCSs tended to fracture as a whole,which was not influenced by relative density of pristine CCSs.It was believed that this work provided a creative way to circumvent the brittleness of CCSs and improve their mechanical performances.展开更多
Ceramic matrix composites(CMC)are widely utilized in high-temperature components of aero-engines for load-bearing and electromagnetic stealth synergy due to their superior toughening and designable electromagnetic pro...Ceramic matrix composites(CMC)are widely utilized in high-temperature components of aero-engines for load-bearing and electromagnetic stealth synergy due to their superior toughening and designable electromagnetic properties.However,the design of ultra-broadband electromagnetic wave(EMW)absorp-tion at thin thicknesses(d<10 mm)has been difficult and focused,especially the design of metama-terial.Inspired by 3D printing technology and the structural characteristic of 2D CMC,this study inge-niously devised and proposed a novel carbon fiber gradient periodic structure in Al_(2)O_(3f)/SiOC composites to enhance the ultra-broadband EMW absorption properties at a wide temperature range.By optimizing the geometric structure parameters,the Al_(2)O_(3f)/SiOC composites with the carbon fiber gradient periodic structure have exhibited exceptional ultra-broadband EMW absorption properties at elevated tempera-tures and excellent mechanical performance.The composites have attained a minimum reflection loss(RLmin)of-30 dB and a high absorption efficiency of more than 84%,ranging from 9.3 to 40 GHz at a thickness of 9 mm.Due to the temperature insensitivity of discrete periodic structures,the composites can adapt to high temperatures up to 700℃.Additionally,compared to the Al_(2)O_(3f)/SiOC composites,the flexural strength and fracture toughness of the Al_(2)O_(3f)/SiOC composites with carbon fiber gradient peri-odic structure have significantly increased to 398 MPa and 15.6 MPa m1/2,respectively.This work breaks through the limitation of the design and fabrication of 3D periodic structures in CMC,creating a novel oxide-CMC with ultra-broadband EMW absorption properties at a wide temperature range and enhanced mechanical properties.展开更多
Satisfactory ionic conductivity,excellent mechanical stability,and high-temperature resistance are the prerequisites for the safe application of solid polymer electrolytes(SPEs)in all-solid-state lithium metal batteri...Satisfactory ionic conductivity,excellent mechanical stability,and high-temperature resistance are the prerequisites for the safe application of solid polymer electrolytes(SPEs)in all-solid-state lithium metal batteries(ASSLMBs).In this study,a novel poly(m-phenylene isophthalamide)(PMIA)-core/poly(ethylene oxide)(PEO)-shell nanofiber membrane and the functional Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)ceramic nanopar-ticle are simultaneously introduced into the PEO-based SPEs to prepare composite polymer electrolytes(CPEs).The core PMIA layer of composite nanofibers can greatly improve the mechanical strength and thermal stability of the CPEs,while the shell PEO layer can provide the 3D continuous transport channels for lithium ions.In addition,the introduction of functional LLZTO nanoparticle not only reduces the crys-tallinity of PEO,but also promotes the dissociation of lithium salts and releases more Li^(+)ions through its interaction with the Lewis acid-base of anions,thereby overall improving the transport of lithium ions.Consequently,the optimized CPEs present high ionic conductivity of 1.38×10^(−4)S/cm at 30℃,signifi-cantly improved mechanical strength(8.5 MPa),remarkable thermal stability(without obvious shrinkage at 150℃),and conspicuous Li dendrites blocking ability(>1800 h).The CPEs also both have good com-patibility and cyclic stability with LiFePO_(4)(>2000 cycles)and high-voltage LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811)(>500 cycles)cathodes.In addition,even at low temperature(40℃),the assembled LiFePO4/CPEs/Li bat-tery still can cycle stably.The novel design can provide an effective way to exploit high-performance solid-state electrolytes.展开更多
A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commerc...A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commercial electron beam melting(EBM?) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell(model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12 g/cm^3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from ~3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography(OM) and scanning electron microscopy(SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha(hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from ~5 μm in the EPBF-fabricated Ti64 to ~1.1 m for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5 μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5 m. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors' knowledge has not been reported before. The results also illustrate the prospects not only for fabricating specialized, novel composite bone replacement scaffolds and implants, through the combination of Ti64 and HA, but also prospects for producing a variety of related metal/ceramic composites using EPBF AM.展开更多
<001>textured Pb(Ni_(1/3)Nb_(2/3))O_(3)-PbZrO_(3)-PbTiO_(3)(PNN-PZT)ceramics were prepared by templated grain growth(TGG)technique using 0.36PNN-x PZ-(0.64-x)PT(x=0.23,0.25 and 0.27)powder matrix.Optimum templat...<001>textured Pb(Ni_(1/3)Nb_(2/3))O_(3)-PbZrO_(3)-PbTiO_(3)(PNN-PZT)ceramics were prepared by templated grain growth(TGG)technique using 0.36PNN-x PZ-(0.64-x)PT(x=0.23,0.25 and 0.27)powder matrix.Optimum template content was derived to achieve the best electromechanical properties of textured ceramics.The piezoelectric coefficient d33=1165 pC/N,Curie temperature T_(C)=197℃,longitudinal mode electrome-chanical coupling factor k33=0.86 and a very large effective piezoelectric strain coefficient d_(33)^(*)=2041 pm/V were simultaneously achieved at the morphotropic phase boundary(MPB)composition(x=0.25)with 3 vol.%BaTiO_(3)(BT)templates.Domain structures of textured ceramics were analyzed in detail to reveal the origin of these high piezoelectric and electromechanical properties.展开更多
In this study,we propose a novel approach to increase the fracture toughness of Al_(2)O_(3)ceramics by incorporating core-shell structural composite whiskers as secondary phases.In particular,Al_(2)O_(3)composite cera...In this study,we propose a novel approach to increase the fracture toughness of Al_(2)O_(3)ceramics by incorporating core-shell structural composite whiskers as secondary phases.In particular,Al_(2)O_(3)composite ceramics reinforced with TiC-coated SiC whiskers(SiCw@TiC)were successfully fabricated through a combination of molten salt synthesis and spark plasma sintering(SPS).The SiC_(w)@TiC whiskers feature a SiC_(w)core and a TiC shell layer(-85 nm thick)composed of nano-sized TiC grains.Remarkably,the core-shell structure is preserved within the Al_(2)O_(3)matrix after sintering,forming a unique composite toughening phase.The interfacial regions surrounding the whiskers exhibit a complex geometric configuration and multidimensional heterogeneities,including variations inphase composition(Al_(2)O_(3)/SiC/TiC),grain size(micron-/nano-scale),and thermal expansion coefficient(3.8×10^(-6)-7.4×10^(-6)/K),which collectively generate a sophisticated stress field.This intricate microstructure enables the SiC_(w)@TiC whiskers to dissipate crack propagation energy through multiple mechanisms,significantly improving the fracture toughness of the Al_(2)O_(3)matrix.The resulting Al_(2)O_(3)-SiC_(w)@TiC composite ceramics demonstrate exceptional mechanical properties,with a relative density of 99.16%±0.48%,Vickers hardness of 21.38±0.93 GPa,flexural strength of 693±49 MPa,and fracture toughness of 7.15±0.47 MPa-m^(1/2).This work establishes a paradigmfor structural ceramictoughening through engineered core-shell architectures.展开更多
We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the...We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration(ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.展开更多
A bulk metal/ceramic composite material with a honeycomb-like micro-cell structure has been prepared by sintering the spherical Al90Mn9Ce1 alloy powders clad by Al2O3 nano-powder with the spark plasma sintering (SPS) ...A bulk metal/ceramic composite material with a honeycomb-like micro-cell structure has been prepared by sintering the spherical Al90Mn9Ce1 alloy powders clad by Al2O3 nano-powder with the spark plasma sintering (SPS) technique. The as-prepared material consists of Al90Mn9Ce1 alloy cell and closed Al2O3 ceramic cell wall. The diameter of the cells is about 20―40 μm, while a thickness of the cell wall is about 1―2 μm. The ultimate compressive strength of the as-sintered materials is about 514 MPa, while its fracture strain is up to about 0.65 %. This composite material might possess good anti-corrosion, thermal endurance and other potential properties due to its unique microstructure. The result shows that the Al90Mn9Ce1/Al2O3 composite powders can be sintered by spark plasma sintering technique despite the large difference in their sintering temperature. This work offers a way of designing and preparing metal/ceramic composite material with functional property.展开更多
Advances in the study of structural ceramic materials have revealed new perspectives and opportunities,with an increasing emphasis on incorporating biomimicry concepts.Carbide ceramics with anisotropic crystal structu...Advances in the study of structural ceramic materials have revealed new perspectives and opportunities,with an increasing emphasis on incorporating biomimicry concepts.Carbide ceramics with anisotropic crystal structures—such as silicon carbide—exhibit superior properties,including high modulus,high-temperature resistance,wear resistance,and high thermal conductivity,making them ideal structural materials.The implementation of biomimetic texturing techniques can enhance their performance along specific orientations,thereby expanding their potential for use in more rigorous environments and endowing them with integrated structural and functional characteristics.This review provides an overview of commonly textured biological materials and discusses their performance.It emphasizes the techniques used to prepare anisotropic carbide ceramics and anisotropic carbide ceramic composites—such as strong external field induction(hot working under uniaxial pressure,casting technologies within magnetic alignment,etc.),template methods(biotemplating,ice templating,etc.),and three-dimensional printing technologies(direct ink writing,stereolithography,etc.)—focusing on the work of researchers within the structural ceramic community,summarizing the current challenges in the preparation of anisotropic carbide ceramic composites,and providing insight into their future development and application.展开更多
In this work, we have studied a new lead-free ceramic of（1-y）Bi1-xNdxFeO3-yBiScO3（0.05≤x≤0.15 and 0.05≤y≤0.15） prepared by a conventional solid-state method, and the influences of Nd and Sc content on their ph...In this work, we have studied a new lead-free ceramic of（1-y）Bi1-xNdxFeO3-yBiScO3（0.05≤x≤0.15 and 0.05≤y≤0.15） prepared by a conventional solid-state method, and the influences of Nd and Sc content on their phase structure and electrical properties were investigated in detail. The ceramics with 0.05≤x≤0.10 and 0.05≤y≤0.15 belong to an R3 c phase, and the rhombohedral-like and orthorhombic multiphase coexistence is established in the composition range of 0.125≤x≤0.15 and y=0. The electrical properties of the ceramics can be enhanced by modifying x and y values. The highest piezoelectric coefficient（d33～51 p C/N） is obtained in the ceramics with x=0.075 and y=0.125, which is superior to that of a pure BiFeO3 ceramic. In addition, a lowest dielectric loss（tan δ～0.095%, f=100 k Hz） is shown in the ceramics with x=0.15 and y=0 due to the involvement of low defect concentrations, and the improved thermal stability of piezoelectricity at 20–600℃ is possessed in the ceramics. We believe that the ceramics can play a meaningful role in the high-temperature lead-free piezoelectric applications.展开更多
超高温陶瓷(Ultra-high Temperature Ceramic,UHTC)结构材料因其在1600℃以上氧化环境中表现出优异的抗氧化/烧蚀性能、高温强度保持率和抗热冲击性能,成为航空航天、国防装备、能源动力等领域的重要候选材料。近年来,围绕UHTC结构材料...超高温陶瓷(Ultra-high Temperature Ceramic,UHTC)结构材料因其在1600℃以上氧化环境中表现出优异的抗氧化/烧蚀性能、高温强度保持率和抗热冲击性能,成为航空航天、国防装备、能源动力等领域的重要候选材料。近年来,围绕UHTC结构材料的成分调控、微观结构设计、先进制备工艺以及性能优化等方面,基础研究和技术应用均取得了显著进展。以碳化物、硼化物、氮化物等为代表的UHTC体系,正面临着温度更高、环境更复杂的服役需求。为进一步推动极端环境用UHTC结构材料的发展,本文系统综述了该领域的最新研究进展。首先,详细阐述了UHTC粉体的合成工艺;其次,深入探讨了超高温结构陶瓷的体系、致密化方法及结构调控策略;继而重点分析了超高温陶瓷基复合材料(Ultra-high Temperature Ceramic Matrix Composites,UHTCMCs)、超高温陶瓷改性碳/碳复合材料(Ultra-high Temperature Ceramics Modified Carbon/Carbon Composites,UHTCs-C/C)以及UHTC涂层的制备技术及其性能强化策略,着重探讨了其在抗氧化/烧蚀领域的最新突破。同时,本文还指出了极端环境下UHTC结构材料在长期稳定性和可靠性方面面临的主要技术挑战,并对其未来发展趋势进行了前瞻性展望。展开更多
基金financially supported by the National Natural Science Foundation of China(No.52275310)the Open Project of State Key Laboratory of Explosion Science and Technology(No.QNKT22-15)the BIT Research and Innovation Promoting Project(No.2022YCX020)。
文摘Benefiting from excellent mechanical properties and low density,cellular ceramic structures(CCSs)are competitive candidates as structural components.However,inherent brittleness from strong chemical bonds among atoms extremely impeded CCSs'application.Natural materials occupied outstanding strength and toughness simultaneously due to the dual-phase interpenetrated structure.Inspired by natural materials,it was proposed to fabricate coating covered and fulfilled polyurea/CCS interpenetrated composites(C/CCSs and B/CCSs)to circumvent the brittleness of 3D-printed Al_(2)O_(3)CCSs.It was demonstrated that polyurea coating had less effect on the compressive strength of C/CCSs but tremendously improved their energy-absorbing ability.The energy-absorbing ability of C/CCSs was improved from26.48-52.57 kJ·m^(-3)of CCSs to 1.04-1.89 MJ·m^(-3)because of the extended plateau stage.Furthermore,compressive strength and energy-absorbing ability of B/CCSs were strengthened to 1.33-1.36 and 2.84-4.61 times of C/CCSs,respectively.Besides,failure mode of C/CCSs changed from localized deformation to fracturing entirely with the increase in relative density of CCSs inside,which was the same as that of CCSs.However,with the help of polyurea coating,C/CCSs were still intact at strains up to60%,which would neve r fail catastrophically as CCSs at low strains.B/CCSs tended to fracture as a whole,which was not influenced by relative density of pristine CCSs.It was believed that this work provided a creative way to circumvent the brittleness of CCSs and improve their mechanical performances.
基金supported by the National Key R&D Program of China(No.2022YFC2204500)the Aviation Science Foundation Project(No.2023Z055053001).
文摘Ceramic matrix composites(CMC)are widely utilized in high-temperature components of aero-engines for load-bearing and electromagnetic stealth synergy due to their superior toughening and designable electromagnetic properties.However,the design of ultra-broadband electromagnetic wave(EMW)absorp-tion at thin thicknesses(d<10 mm)has been difficult and focused,especially the design of metama-terial.Inspired by 3D printing technology and the structural characteristic of 2D CMC,this study inge-niously devised and proposed a novel carbon fiber gradient periodic structure in Al_(2)O_(3f)/SiOC composites to enhance the ultra-broadband EMW absorption properties at a wide temperature range.By optimizing the geometric structure parameters,the Al_(2)O_(3f)/SiOC composites with the carbon fiber gradient periodic structure have exhibited exceptional ultra-broadband EMW absorption properties at elevated tempera-tures and excellent mechanical performance.The composites have attained a minimum reflection loss(RLmin)of-30 dB and a high absorption efficiency of more than 84%,ranging from 9.3 to 40 GHz at a thickness of 9 mm.Due to the temperature insensitivity of discrete periodic structures,the composites can adapt to high temperatures up to 700℃.Additionally,compared to the Al_(2)O_(3f)/SiOC composites,the flexural strength and fracture toughness of the Al_(2)O_(3f)/SiOC composites with carbon fiber gradient peri-odic structure have significantly increased to 398 MPa and 15.6 MPa m1/2,respectively.This work breaks through the limitation of the design and fabrication of 3D periodic structures in CMC,creating a novel oxide-CMC with ultra-broadband EMW absorption properties at a wide temperature range and enhanced mechanical properties.
基金supported by the National Natural Science Foundation of China (Nos.52203066,51973157,61904123)the Tianjin Natural Science Foundation (No.18JCQNJC02900)+3 种基金National Innovation and Entrepreneurship Training Program for College students (No.202310058007)Tianjin Municipal College Students’ Innovation and Entrepreneurship Training Program (No.202310058088)Science & Technology Development Fund of Tianjin Education Commission for Higher Education (No.2018KJ196)State Key Laboratory of Membrane and Membrane Separation,Tiangong University
文摘Satisfactory ionic conductivity,excellent mechanical stability,and high-temperature resistance are the prerequisites for the safe application of solid polymer electrolytes(SPEs)in all-solid-state lithium metal batteries(ASSLMBs).In this study,a novel poly(m-phenylene isophthalamide)(PMIA)-core/poly(ethylene oxide)(PEO)-shell nanofiber membrane and the functional Li_(6.4)La_(3)Zr_(1.4)Ta_(0.6)O_(12)(LLZTO)ceramic nanopar-ticle are simultaneously introduced into the PEO-based SPEs to prepare composite polymer electrolytes(CPEs).The core PMIA layer of composite nanofibers can greatly improve the mechanical strength and thermal stability of the CPEs,while the shell PEO layer can provide the 3D continuous transport channels for lithium ions.In addition,the introduction of functional LLZTO nanoparticle not only reduces the crys-tallinity of PEO,but also promotes the dissociation of lithium salts and releases more Li^(+)ions through its interaction with the Lewis acid-base of anions,thereby overall improving the transport of lithium ions.Consequently,the optimized CPEs present high ionic conductivity of 1.38×10^(−4)S/cm at 30℃,signifi-cantly improved mechanical strength(8.5 MPa),remarkable thermal stability(without obvious shrinkage at 150℃),and conspicuous Li dendrites blocking ability(>1800 h).The CPEs also both have good com-patibility and cyclic stability with LiFePO_(4)(>2000 cycles)and high-voltage LiNi_(0.8)Mn_(0.1)Co_(0.1)O_(2)(NMC811)(>500 cycles)cathodes.In addition,even at low temperature(40℃),the assembled LiFePO4/CPEs/Li bat-tery still can cycle stably.The novel design can provide an effective way to exploit high-performance solid-state electrolytes.
文摘A novel, Ti-6 Al-4 V(Ti64)/Hydroxyapatite(HA at 5% by weight concentration) metal/ceramic composite has been fabricated using electron beam powder bed fusion(EPBF) additive manufacturing(AM): specifically, the commercial electron beam melting(EBM?) process. In addition to solid Ti64 and Ti64/5% HA samples, four different unit cell(model) open-cellular mesh structures for the Ti64/5% HA composite were fabricated having densities ranging from 0.68 to 1.12 g/cm^3, and corresponding Young's moduli ranging from 2.9 to 8.0 GPa, and compressive strengths ranging from ~3 to 11 MPa. The solid Ti64/5%HA composite exhibited an optimal tensile strength of 123 MPa, and elongation of 5.5% in contrast to a maximum compressive strength of 875 MPa. Both the solid composite and mesh samples deformed primarily by brittle deformation, with the mesh samples exhibiting erratic, brittle crushing. Solid, EPBF-fabricated Ti64 samples had a Vickers microindentation hardness of 4.1 GPa while the Ti64/5%HA solid composite exhibited a Vickers microindentation hardness of 6.8 GPa. The lowest density Ti64/5%HA composite mesh strut sections had a Vickers microindentation hardness of 7.1 GPa. Optical metallography(OM) and scanning electron microscopy(SEM) analysis showed the HA dispersoids to be highly segregated along domain or grain boundaries, but homogeneously distributed along alpha(hcp) platelet boundaries within these domains in the Ti64 matrix for both the solid and mesh composites. The alpha platelet width varied from ~5 μm in the EPBF-fabricated Ti64 to ~1.1 m for the Ti64/5%HA mesh strut. The precursor HA powder diameter averaged 5 μm, in contrast to the dispersed HA particle diameters in the Ti64/5%HA composite which averaged 0.5 m. This work highlights the use of EPBF AM as a novel process for fabrication of a true composite structure, consisting of a Ti64 matrix and interspersed and exposed HA domains, which to the authors' knowledge has not been reported before. The results also illustrate the prospects not only for fabricating specialized, novel composite bone replacement scaffolds and implants, through the combination of Ti64 and HA, but also prospects for producing a variety of related metal/ceramic composites using EPBF AM.
基金supported in part by the Natural Science Foun-dation of Heilongjiang Province(No.LH2022E048)Postdoctoral Science Foundation of Heilongjiang Province(No.LBH-Z22138)China National Postdoctoral Program for Innovative Talents(No.BX20490103).
文摘<001>textured Pb(Ni_(1/3)Nb_(2/3))O_(3)-PbZrO_(3)-PbTiO_(3)(PNN-PZT)ceramics were prepared by templated grain growth(TGG)technique using 0.36PNN-x PZ-(0.64-x)PT(x=0.23,0.25 and 0.27)powder matrix.Optimum template content was derived to achieve the best electromechanical properties of textured ceramics.The piezoelectric coefficient d33=1165 pC/N,Curie temperature T_(C)=197℃,longitudinal mode electrome-chanical coupling factor k33=0.86 and a very large effective piezoelectric strain coefficient d_(33)^(*)=2041 pm/V were simultaneously achieved at the morphotropic phase boundary(MPB)composition(x=0.25)with 3 vol.%BaTiO_(3)(BT)templates.Domain structures of textured ceramics were analyzed in detail to reveal the origin of these high piezoelectric and electromechanical properties.
基金supported by the Central Government Guided Local Science and Technology Development Fund Project(No.226Z1101G)the Science and Technology Research Project of Universities in Hebei Province(No.CXY2024033)the Hebei Yanzhao Golden Platform backbone Talent Project(Platform for returning to China)(No.A2024008).
文摘In this study,we propose a novel approach to increase the fracture toughness of Al_(2)O_(3)ceramics by incorporating core-shell structural composite whiskers as secondary phases.In particular,Al_(2)O_(3)composite ceramics reinforced with TiC-coated SiC whiskers(SiCw@TiC)were successfully fabricated through a combination of molten salt synthesis and spark plasma sintering(SPS).The SiC_(w)@TiC whiskers feature a SiC_(w)core and a TiC shell layer(-85 nm thick)composed of nano-sized TiC grains.Remarkably,the core-shell structure is preserved within the Al_(2)O_(3)matrix after sintering,forming a unique composite toughening phase.The interfacial regions surrounding the whiskers exhibit a complex geometric configuration and multidimensional heterogeneities,including variations inphase composition(Al_(2)O_(3)/SiC/TiC),grain size(micron-/nano-scale),and thermal expansion coefficient(3.8×10^(-6)-7.4×10^(-6)/K),which collectively generate a sophisticated stress field.This intricate microstructure enables the SiC_(w)@TiC whiskers to dissipate crack propagation energy through multiple mechanisms,significantly improving the fracture toughness of the Al_(2)O_(3)matrix.The resulting Al_(2)O_(3)-SiC_(w)@TiC composite ceramics demonstrate exceptional mechanical properties,with a relative density of 99.16%±0.48%,Vickers hardness of 21.38±0.93 GPa,flexural strength of 693±49 MPa,and fracture toughness of 7.15±0.47 MPa-m^(1/2).This work establishes a paradigmfor structural ceramictoughening through engineered core-shell architectures.
基金Funded by the National Natural Science Foundation of China(No.51472092)
文摘We studied the characteristics of two-scale pore structure of preform in the deposition process and the mass transfer of reactant gas in dual-scale pores, and observed the physiochemical phenomenon associated with the reaction. Thereby, we established mathematical models on two scales, respectively, preform and reactor. These models were used for the numerical simulation of the process of ceramic matrix composites densified by isothermal chemical vapor infiltration(ICVI). The models were used to carry out a systematic study on the influence of process conditions and the preform structure on the densification behaviors. The most important findings of our study are that the processing time could be reduced by about 50% without compromising the quality of the material, if the processing temperature is 950-1 000 ℃ for the first 70 hours and then raised to 1 100 ℃.
基金This work was supported by the China Postdoctoral Science Foundation(No.2003033133)the Basic Science Research Foundation of Tsinghua University(Grant No.091201107)the National Center for Nanoscience and Technology of China.
文摘A bulk metal/ceramic composite material with a honeycomb-like micro-cell structure has been prepared by sintering the spherical Al90Mn9Ce1 alloy powders clad by Al2O3 nano-powder with the spark plasma sintering (SPS) technique. The as-prepared material consists of Al90Mn9Ce1 alloy cell and closed Al2O3 ceramic cell wall. The diameter of the cells is about 20―40 μm, while a thickness of the cell wall is about 1―2 μm. The ultimate compressive strength of the as-sintered materials is about 514 MPa, while its fracture strain is up to about 0.65 %. This composite material might possess good anti-corrosion, thermal endurance and other potential properties due to its unique microstructure. The result shows that the Al90Mn9Ce1/Al2O3 composite powders can be sintered by spark plasma sintering technique despite the large difference in their sintering temperature. This work offers a way of designing and preparing metal/ceramic composite material with functional property.
基金Financial support from the National Natural Science Foundation of China(Nos.52073299 and U23A20563)the Shanghai Sailing Program(No.22YF1455700)are gratefully acknowledged.
文摘Advances in the study of structural ceramic materials have revealed new perspectives and opportunities,with an increasing emphasis on incorporating biomimicry concepts.Carbide ceramics with anisotropic crystal structures—such as silicon carbide—exhibit superior properties,including high modulus,high-temperature resistance,wear resistance,and high thermal conductivity,making them ideal structural materials.The implementation of biomimetic texturing techniques can enhance their performance along specific orientations,thereby expanding their potential for use in more rigorous environments and endowing them with integrated structural and functional characteristics.This review provides an overview of commonly textured biological materials and discusses their performance.It emphasizes the techniques used to prepare anisotropic carbide ceramics and anisotropic carbide ceramic composites—such as strong external field induction(hot working under uniaxial pressure,casting technologies within magnetic alignment,etc.),template methods(biotemplating,ice templating,etc.),and three-dimensional printing technologies(direct ink writing,stereolithography,etc.)—focusing on the work of researchers within the structural ceramic community,summarizing the current challenges in the preparation of anisotropic carbide ceramic composites,and providing insight into their future development and application.
基金supported by the National Natural Science Foundation of China(Grant Nos.51102173&51472169)the College of Materials Science and Engineering of Sichuan University
文摘In this work, we have studied a new lead-free ceramic of（1-y）Bi1-xNdxFeO3-yBiScO3（0.05≤x≤0.15 and 0.05≤y≤0.15） prepared by a conventional solid-state method, and the influences of Nd and Sc content on their phase structure and electrical properties were investigated in detail. The ceramics with 0.05≤x≤0.10 and 0.05≤y≤0.15 belong to an R3 c phase, and the rhombohedral-like and orthorhombic multiphase coexistence is established in the composition range of 0.125≤x≤0.15 and y=0. The electrical properties of the ceramics can be enhanced by modifying x and y values. The highest piezoelectric coefficient（d33～51 p C/N） is obtained in the ceramics with x=0.075 and y=0.125, which is superior to that of a pure BiFeO3 ceramic. In addition, a lowest dielectric loss（tan δ～0.095%, f=100 k Hz） is shown in the ceramics with x=0.15 and y=0 due to the involvement of low defect concentrations, and the improved thermal stability of piezoelectricity at 20–600℃ is possessed in the ceramics. We believe that the ceramics can play a meaningful role in the high-temperature lead-free piezoelectric applications.
文摘超高温陶瓷(Ultra-high Temperature Ceramic,UHTC)结构材料因其在1600℃以上氧化环境中表现出优异的抗氧化/烧蚀性能、高温强度保持率和抗热冲击性能,成为航空航天、国防装备、能源动力等领域的重要候选材料。近年来,围绕UHTC结构材料的成分调控、微观结构设计、先进制备工艺以及性能优化等方面,基础研究和技术应用均取得了显著进展。以碳化物、硼化物、氮化物等为代表的UHTC体系,正面临着温度更高、环境更复杂的服役需求。为进一步推动极端环境用UHTC结构材料的发展,本文系统综述了该领域的最新研究进展。首先,详细阐述了UHTC粉体的合成工艺;其次,深入探讨了超高温结构陶瓷的体系、致密化方法及结构调控策略;继而重点分析了超高温陶瓷基复合材料(Ultra-high Temperature Ceramic Matrix Composites,UHTCMCs)、超高温陶瓷改性碳/碳复合材料(Ultra-high Temperature Ceramics Modified Carbon/Carbon Composites,UHTCs-C/C)以及UHTC涂层的制备技术及其性能强化策略,着重探讨了其在抗氧化/烧蚀领域的最新突破。同时,本文还指出了极端环境下UHTC结构材料在长期稳定性和可靠性方面面临的主要技术挑战,并对其未来发展趋势进行了前瞻性展望。
