The magnetic field provided by magnetized SrFe_(12)O_(19)particles in FeSi/SrFe_(12)O_(19)composites is used to replace the applied transverse magnetic field,which successfully reduces the magnetic loss of the composi...The magnetic field provided by magnetized SrFe_(12)O_(19)particles in FeSi/SrFe_(12)O_(19)composites is used to replace the applied transverse magnetic field,which successfully reduces the magnetic loss of the composites with minor reduction of permeability.This magnetic loss reduction mainly comes from the decrease in hysteresis loss,while the eddy current loss is basically unaffected.The hysteresis loss reduction in magnetized composites is believed to be due to the decrease in domain wall displacement caused by the increase in the average magnetic domain size in a DC magnetic field.This is an effective method for reducing the magnetic loss of soft magnetic composites with wide application potential,and there is no problem of increasing the cost and the volume of the magnetic cores.展开更多
Finding the optimum balance between strength and toughness,as well as acquiring reliable thermal shock resistance and oxidation resistance,has always been the most concerned topic in the discussion of ultra-high tempe...Finding the optimum balance between strength and toughness,as well as acquiring reliable thermal shock resistance and oxidation resistance,has always been the most concerned topic in the discussion of ultra-high temperature ceramic composites.Herein,PyC modified 3D carbon fiber is used to reinforce ultra-high temperature ceramic(UHTC).The macroscopic block composite with large size is successfully fabricated through low temperature sintering at 1300℃without pressure.The prepared PyC modified 3D C_(f)/ZrC-SiC composites simultaneously possess excellent physical and chemical stability under the synergistic effect of PyC interface layer and low temperature 1/2 sintering without pressure.The fracture toughness is increased in magnitude to 13.05±1.72 MPa·m^(1/2)accompanied by reliable flexural strength of 251±27 MPa.After rapid thermal shock spanning from room temperature(RT)to 1200℃,there are no visible surface penetrating cracks,spalling,or structural fragmentation.The maximum critical temperature difference reaches 875℃,which is nearly three times higher than that of traditional monolithic ceramics.The haunting puzzle of intrinsic brittleness and low damage tolerance are resolved fundamentally.Under the protection of PyC interface layer,the carbon fibers around oxide layer and matrix remain structure intact after static oxidation at 1500℃for 30 min.The oxide layer has reliable physical and chemical stability and resists the erosion from fierce oxidizing atmosphere,ensuring the excellent oxidation resistance of the composites.In a sense,the present work provides promising universality in designability and achievement of 3D carbon fiber reinforced ceramic composites.展开更多
To further improve the oxidation resistance of polymer derived ceramic(PDC)composites in harsh environments,Cf/SiC/SiHfBOC composites were prepared by chemical vapor infiltration(CVI)and precursor impregnation pyrolys...To further improve the oxidation resistance of polymer derived ceramic(PDC)composites in harsh environments,Cf/SiC/SiHfBOC composites were prepared by chemical vapor infiltration(CVI)and precursor impregnation pyrolysis(PIP)methods.The weight retention change,mechanical properties,and microstructure of C/SiC/SiHfBOC before and after oxidation in air were studied in details.Microscopic analyses showed that only the interface between the ceramics and fibers was oxidized to some extent,and hafnium had been enriched on the composite surface after oxidizing at different temperature.The main oxidation products of Cf/SiC/SiHfBOC composites were Hf0_(2)and HfSi04 after oxidation at 1500℃for 60 min.Moreover,the weight retention ratio and compressive strength of the Cf/SiC/SiHfBOC composites are 83.97%and 23.88±3.11 MPa,respectively.It indicates that the Cf/SiC/SiHfBOC composites should be promising to be used for a short time in the oxidation environment at 1500℃.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51872004 and 51802002)the Key Program of the Education Department of Anhui Province,China(Grant No.KJ2019ZD03)the Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Specials Environments(Grant No.6142905202112)。
文摘The magnetic field provided by magnetized SrFe_(12)O_(19)particles in FeSi/SrFe_(12)O_(19)composites is used to replace the applied transverse magnetic field,which successfully reduces the magnetic loss of the composites with minor reduction of permeability.This magnetic loss reduction mainly comes from the decrease in hysteresis loss,while the eddy current loss is basically unaffected.The hysteresis loss reduction in magnetized composites is believed to be due to the decrease in domain wall displacement caused by the increase in the average magnetic domain size in a DC magnetic field.This is an effective method for reducing the magnetic loss of soft magnetic composites with wide application potential,and there is no problem of increasing the cost and the volume of the magnetic cores.
基金supported by Key Program of National Natural Science Foundation of China(No.52032003)National Natural Science Foundation of China(Nos.51872059 and 51772061)+2 种基金Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Special Environments(No.6142905202112)China Postdoctoral Science Foundation(No.2021M690817)Heilongjiang Provincial Postdoctoral Science Foundation(No.LBH-Z20144).
文摘Finding the optimum balance between strength and toughness,as well as acquiring reliable thermal shock resistance and oxidation resistance,has always been the most concerned topic in the discussion of ultra-high temperature ceramic composites.Herein,PyC modified 3D carbon fiber is used to reinforce ultra-high temperature ceramic(UHTC).The macroscopic block composite with large size is successfully fabricated through low temperature sintering at 1300℃without pressure.The prepared PyC modified 3D C_(f)/ZrC-SiC composites simultaneously possess excellent physical and chemical stability under the synergistic effect of PyC interface layer and low temperature 1/2 sintering without pressure.The fracture toughness is increased in magnitude to 13.05±1.72 MPa·m^(1/2)accompanied by reliable flexural strength of 251±27 MPa.After rapid thermal shock spanning from room temperature(RT)to 1200℃,there are no visible surface penetrating cracks,spalling,or structural fragmentation.The maximum critical temperature difference reaches 875℃,which is nearly three times higher than that of traditional monolithic ceramics.The haunting puzzle of intrinsic brittleness and low damage tolerance are resolved fundamentally.Under the protection of PyC interface layer,the carbon fibers around oxide layer and matrix remain structure intact after static oxidation at 1500℃for 30 min.The oxide layer has reliable physical and chemical stability and resists the erosion from fierce oxidizing atmosphere,ensuring the excellent oxidation resistance of the composites.In a sense,the present work provides promising universality in designability and achievement of 3D carbon fiber reinforced ceramic composites.
基金supported by the Key Program of the National Natural Science Foundation of China(No.52032003)the National Natural Science Foundation of China(Nos.519720820 and 51772061)+1 种基金the Science Foundation of the National Key Laboratory of Science and Technology on Advanced Composites in Special Environments(No.6142905202112)the Heilongjiang Provincial Postdoctoral Science Foundation(No.LBH-Z20144).
文摘To further improve the oxidation resistance of polymer derived ceramic(PDC)composites in harsh environments,Cf/SiC/SiHfBOC composites were prepared by chemical vapor infiltration(CVI)and precursor impregnation pyrolysis(PIP)methods.The weight retention change,mechanical properties,and microstructure of C/SiC/SiHfBOC before and after oxidation in air were studied in details.Microscopic analyses showed that only the interface between the ceramics and fibers was oxidized to some extent,and hafnium had been enriched on the composite surface after oxidizing at different temperature.The main oxidation products of Cf/SiC/SiHfBOC composites were Hf0_(2)and HfSi04 after oxidation at 1500℃for 60 min.Moreover,the weight retention ratio and compressive strength of the Cf/SiC/SiHfBOC composites are 83.97%and 23.88±3.11 MPa,respectively.It indicates that the Cf/SiC/SiHfBOC composites should be promising to be used for a short time in the oxidation environment at 1500℃.
