Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application f...Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.展开更多
Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suita...Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.展开更多
基金National Natural Science Foundation of China(52222202)National Key R&D Program of China(2022YFB3707700)+2 种基金Project of Shanghai Science and Technology Innovation Action Plan(21511104800)Shanghai Pilot Program for Basic Research-Chinese Academy of Science,Shanghai Branch(JCYJ-SHFY-2021-001)Science Center for Gas Turbine Project(P2022-B-Ⅳ-001-001)。
文摘Silicon-carbide-fiber-reinforced silicon-carbide-ceramic-based matrix(SiC/SiC)composites possess excellent properties such as low density,high strength and high temperature resistance,showing a potential application for structural components in the aerospace field,but their oxidation behavior remains largely unknown.In this study,Yb_(2)Si_(2)O_(7)modified SiC/SiC(SiC/SiC-Yb_(2)Si_(2)O_(7))mini-composites were prepared by introducing Yb_(2)Si_(2)O_(7)as anti-oxidation phase into SiC fiber bundles via Sol-Gel and depositing SiC matrix by chemical vapor deposition(CVD).Influence of Yb_(2)Si_(2)O_(7)on microstructure,mechanical property and oxidation behavior of SiC/SiC mini-composites was investigated.The results showed that after oxidation in air at 1200 and 1400℃for 50 h,the tensile strength retentions of SiC/SiC mini-composites were 77%and 69%,respectively,and the fracture morphology exhibited flat.The Yb_(2)Si_(2)O_(7)introduced by Sol-Gel partially distributed in layers,contributing to the toughening of the material.On the fracture surface,there was interlayer debonding,which extended energy dissipation mechanism of SiC/SiC mini-composites.Tensile strength of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites at room temperature was 484 MPa.After oxidation in air at 1200 and 1400℃for 50 h,the tensile strengths decreased to 425 and 374 MPa,resulting in retention rates of 88%and 77%,respectively.It displayed typical non-brittle fracture characteristics.The interface oxygen content of SiC/SiC mini-composites at the fracture surface was higher than that of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites,indicating that introduction of Yb_(2)Si_(2)O_(7)could alleviate oxygen diffusion towards the interface,and therefore improve the oxidation resistance of SiC/SiC-Yb_(2)Si_(2)O_(7)mini-composites.
基金Student Training Program for Innovation and Entrepreneurship of Hangzhou Institute for Advanced Study,UCAS(CXCY20230305)Chinese Academy of Sciences Key Project(ZDRW-CN-2021-3-1-18)。
文摘Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.
