Reactive melt infiltration(RMI)is an effective method for fabrication of highly dense carbon fiber reinforced ultra-high temperature ceramic matrix composites(Cf/UHTCs).In this work,C_(f)/SiC-ZrC-ZrB_(2)composites wer...Reactive melt infiltration(RMI)is an effective method for fabrication of highly dense carbon fiber reinforced ultra-high temperature ceramic matrix composites(Cf/UHTCs).In this work,C_(f)/SiC-ZrC-ZrB_(2)composites were fabricated by infiltrating ZrSi_(2)melt into porous C_(f)/B_(4)C-C preforms,where the physical and chemical reactions involved during the RMI process were identified and analyzed.Inhomogeneous infiltration between the inter-and intra-bundle pores was revealed,and was found to be strongly related to the pore structures of the C_(f)/B_(4)C-C preform.It is indicated that the inhomogeneous infiltration can be mitigated remarkably with increasing porosity and pore size of the preform.The effect of pore size on the RMI process was also investigated by a quantitative model,which agrees very well with the experiment results.It further indicates that the inhomogeneous infiltration can also be relieved at elevated RMI temperature.However,excessive infiltration at elevated temperature or more porous preform may cause serious erosion on interphase and fibers,leading to mechanical properties deterioration of the final composites.展开更多
To study the influence of B4C particle size on the microstructure and damping capacities of(B_(4)C+Ti)/Mg composites,in situ reactive infiltration technique was utilized to prepare Mg-matrix composites.The microstruct...To study the influence of B4C particle size on the microstructure and damping capacities of(B_(4)C+Ti)/Mg composites,in situ reactive infiltration technique was utilized to prepare Mg-matrix composites.The microstructure,produced phases and damping capacities of the composites prepared with different particle size of B4C were characterized and analyzed.The results show that the reaction between B4C and Ti tends to be more complete when finer B_(4)C particle was used to prepare the composites.But the microstructure of the as-prepared composites is more homogenous when B4C and Ti have similar particle size.The strain-dependent damping capacities of(B_(4)C+Ti)/Mg composites improve gradually with the increase of strain amplitude,and composites prepared with coarser B4C particles tend to have higher damping capacities.The temperature-dependent damping capacities improve with increasing the measuring temperatures,and the kind of damping capacities of the composites prepared with 5mm B4C are inferior to those of coarser particles.The dominant damping mechanism for the strain-damping capacity is dislocation damping and plastic zone damping,while that for the temperature-damping capacity is interface damping or grain boundary damping.展开更多
The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditiona...The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix.Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi_(2),C/C-ZrB_(2)-ZrC-SiC composites prepared by the vacuum infiltration of ZrB_(2) combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases.The mass and linear ablation rates of the C/C-ZrB_(2)-ZrC-SiC composites were respectively 68.9%and 29.7%lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration.The ablation performance was improved because the volatilization of B_(2)O_(3),removes some of the heat,and the more uniformly distributed ZrO_(2),that helps produce a ZrO2-SiO2 continu-ous protective layer,hinders oxygen infiltration and decreases ablation.展开更多
To obtain high-performance Zr-based ultra-high-temperature composites,Zr-based ultra-high-temperature gradient composites were prepared by changing the laying method of the infiltrant via reactive melt infiltration.Th...To obtain high-performance Zr-based ultra-high-temperature composites,Zr-based ultra-high-temperature gradient composites were prepared by changing the laying method of the infiltrant via reactive melt infiltration.The effects of different infiltrant laying methods on the microstructure and ablative properties of Zr-based ultrahigh-temperature gradient composites were investigated.The results showed that the gradient structure of the Zr-based ultrahigh-temperature gradient composites differed when the composition ratio of the infiltrant was changed.When the thicknesses of the Zr/Mo/Si layers were 6/4/12 mm and 8/2/12 mm,the SiMoZrC solid solution content in the samples increased and decreased along the infiltration direction,respectively.The gradient samples were ablated in an oxyacetylene flame at 3000°C for 40 s.The ablation resistance of the sample was the highest when the infiltrant was a powder and the thickness of the Zr/Mo/Si layer was 6/4/12 mm.展开更多
ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to...ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZB展开更多
Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the compo...Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the composites before and after erosion.The results indicate that a U shape relationship curve presents between the erosion rates and Al content,and the lowest erosion rate occurs at 40 wt%Al.Except for the important influence of compactness,the increasing soft Al mixed with reactive SiC,namely the mixture located between carbon and residual Si also,plays a key role in the erosion of the C/C-SiC composites through crack deflection,plastic deformation and bonding cracked Si.展开更多
BACKGROUND Reactive lymphoid hyperplasia(RLH)of the liver is a rare liver lesion.It is considered difficult to differentiate radiologically from hepatocellular carcinoma,metastatic liver tumor and other pathologies.CA...BACKGROUND Reactive lymphoid hyperplasia(RLH)of the liver is a rare liver lesion.It is considered difficult to differentiate radiologically from hepatocellular carcinoma,metastatic liver tumor and other pathologies.CASE SUMMARY A 54-year-old woman presented to our hospital with RLH of the liver.The patient had a diagnosis of metastatic carcinoma of the liver from an unknown origin and subsequently underwent partial hepatectomy.However,histopathological analysis revealed RLH.The lesion showed perinodular enhancement in the arterial phase on contrast-enhanced computed tomography and magnetic resonance imaging.On diffusion-weighted imaging(DWI),we encountered linear hyperintensity along the portal tract consecutive to the liver lesion,which is a new characteristic radiologic finding.This finding corresponded to the lymphoid cell infiltration of the portal tract.Furthermore,there was strongly restricted diffusion on the apparent diffusion coefficient map.We used these characteristic radiologic findings to diagnose the lesion as a lymphoproliferative disease.CONCLUSION The linear hyperintensity consecutive to the liver lesion on DWI provided additional valuable diagnostic information.展开更多
To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method...To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method,the high-temperature thermal stability of the composites was systematically studied by changing the temperature and holding time of thermal treatment.Results show that the mass loss rate of low Si composites has a growth trend with increasing temperature,and a crystal transformation from β-SiC toα-SiC occurs in the composites.In the calibrated area,SiC phase experiences Ostwald ripening and volume change with location migration,while ZrC phase experiences a re-sintering process with diffusion.Moreover,it is found that increasing temperature has a more obvious effect on the thermal stability than extending holding time,which is mainly attributed to the faster diffusion rate of atoms.展开更多
ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-syn...ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.展开更多
The reactive cast-infiltration technique was used to produce an Fe-WC surface composite layer on an iron casting, in which the WC particulates were formed in situ from a reaction of W with C. The structure and phase c...The reactive cast-infiltration technique was used to produce an Fe-WC surface composite layer on an iron casting, in which the WC particulates were formed in situ from a reaction of W with C. The structure and phase construction of the surface composite were evaluated by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDS), etc. An Fe-WC surface composite layer with a volume fraction of WC particles up to 30％ and particle size in the range 10～30 μm was successfully produced. Abrasive resistance test results show that the Fe-WC surface composite layer possesses great abrasive resistance.展开更多
C/C-SiC composites have the potentiality to be applied in shield pumps of nuclear reactors as the bearing material because of their low density,good mechanical properties and excellent tribological properties.The C/C-...C/C-SiC composites have the potentiality to be applied in shield pumps of nuclear reactors as the bearing material because of their low density,good mechanical properties and excellent tribological properties.The C/C-SiC composites are fabricated via reactive melt infiltration(RMI)using silicon liquid infiltrated in C/C matrix composites.Friction and wear behaviors of C/C-SiC composites under water lubricated conditions are investigated using the block-on-ring test at room temperature,and compared with those of the resin graphite which is used as the bearing material in shield pumps at present.In addition,friction and wear mechanisms of C/C-SiC composites under water lubricated conditions have been discussed.Results show that tensile strengths of C/C-SiC composites are 150210 MPa,and compressive strengths are 403536 MPa.Friction and wear behaviors of C/C-SiC composites are closely related to the load and the speed.The time to reach a stable friction status decreases with the increase of the speed.Though the friction coefficient of C/C-SiC composites under water lubricated conditions is slightly higher than that of graphite,the wear rate of C/C-SiC composites is much lower,which suggests that the C/C-SiC composites can sustain a longer life during operation.展开更多
Cobalt-silicon based carbon composites(Co–Si/C)have established a noteworthy consideration in recent years as a replacement for conventional materials in the automotive and aerospace industries.To achieve the composi...Cobalt-silicon based carbon composites(Co–Si/C)have established a noteworthy consideration in recent years as a replacement for conventional materials in the automotive and aerospace industries.To achieve the composite,a reactive melt infiltration process(RMI)is used,in which a melt impregnates a porous preform by capillary force.This method promises a high-volume fraction of reinforcement and can be steered in such a way to get the good“near-net”shaped components.A mathematical model is developed using reaction-formed Co–Si alloy/C composite as a prototype system for this process.The wetting behavior and contact angle are discussed;surface tension and viscosity are calculated by Wang’s and Egry’s equations,respectively.Pore radii of 5μm and 10μm are set as a reference on highly oriented pyrolytic graphite.The graphs are plotted using the model,to study some aspects of the infiltration dynamics.This highlights the possible connections among the various processes.In this attempt,the Co–Si(62.5 at.%silicon)alloy’s maximum infiltration at 5μm and 10μm radii are found as 0.05668 m at 125 s and 0.22674 m at 250 s,respectively.展开更多
To meet the increasing demand for advanced materials capable of operation over 2000 ℃ for future thermal protection systems application, C/C-ZrC-SiC composites were fabricated by reactive melt infiltration （RMI） wi...To meet the increasing demand for advanced materials capable of operation over 2000 ℃ for future thermal protection systems application, C/C-ZrC-SiC composites were fabricated by reactive melt infiltration （RMI） with Zr, Si mixed powders as raw materials. The structural evolution and formation mechanism of the C/C- ZrC-SiC composites were discussed, and the mechanical property of the as-prepared material was investigated by compression test. The results showed that after the RMI process, a special structure with ZrC-SiC multi-coating as outer layer and ZrC-SiC-PyC ceramics as inner matrix was formed. ZrC and SiC rich areas were formed in the composites and on the coating surface due to the formation of Zr-Si intermetallic compounds in the RMI process. Mechanical tests showed that the average compression strength of the C/C-ZrC-SiC composites was 133.86 MPa, and the carbon fibers in the composites were not seriously damaged after the RMI process.展开更多
基金The financial support from“The National Key Research and Development Program of China”(No.2017YFB0703200)“National Natural Science Foundation of China”(No.51702341)+1 种基金Chinese Academy of Sciences Innovative Funding(CXJJ-17-M169)“CAS Pioneer Hundred Talents Program”are greatly acknowledged.
文摘Reactive melt infiltration(RMI)is an effective method for fabrication of highly dense carbon fiber reinforced ultra-high temperature ceramic matrix composites(Cf/UHTCs).In this work,C_(f)/SiC-ZrC-ZrB_(2)composites were fabricated by infiltrating ZrSi_(2)melt into porous C_(f)/B_(4)C-C preforms,where the physical and chemical reactions involved during the RMI process were identified and analyzed.Inhomogeneous infiltration between the inter-and intra-bundle pores was revealed,and was found to be strongly related to the pore structures of the C_(f)/B_(4)C-C preform.It is indicated that the inhomogeneous infiltration can be mitigated remarkably with increasing porosity and pore size of the preform.The effect of pore size on the RMI process was also investigated by a quantitative model,which agrees very well with the experiment results.It further indicates that the inhomogeneous infiltration can also be relieved at elevated RMI temperature.However,excessive infiltration at elevated temperature or more porous preform may cause serious erosion on interphase and fibers,leading to mechanical properties deterioration of the final composites.
基金Project(51901095)supported by the National Natural Science Foundation of China。
文摘To study the influence of B4C particle size on the microstructure and damping capacities of(B_(4)C+Ti)/Mg composites,in situ reactive infiltration technique was utilized to prepare Mg-matrix composites.The microstructure,produced phases and damping capacities of the composites prepared with different particle size of B4C were characterized and analyzed.The results show that the reaction between B4C and Ti tends to be more complete when finer B_(4)C particle was used to prepare the composites.But the microstructure of the as-prepared composites is more homogenous when B4C and Ti have similar particle size.The strain-dependent damping capacities of(B_(4)C+Ti)/Mg composites improve gradually with the increase of strain amplitude,and composites prepared with coarser B4C particles tend to have higher damping capacities.The temperature-dependent damping capacities improve with increasing the measuring temperatures,and the kind of damping capacities of the composites prepared with 5mm B4C are inferior to those of coarser particles.The dominant damping mechanism for the strain-damping capacity is dislocation damping and plastic zone damping,while that for the temperature-damping capacity is interface damping or grain boundary damping.
文摘The development of advanced aircraft relies on high performance thermal-structural materials,and carbon/carbon com-posites(C/C)composited with ultrahigh-temperature ceramics are ideal candidates.However,the traditional routes of compositing are either inefficient and expensive or lead to a non-uniform distribution of ceramics in the matrix.Compared with the traditional C/C-ZrC-SiC composites prepared by the reactive melt infiltration of ZrSi_(2),C/C-ZrB_(2)-ZrC-SiC composites prepared by the vacuum infiltration of ZrB_(2) combined with reactive melt infiltration have the higher content and more uniform distribution of the introduced ceramic phases.The mass and linear ablation rates of the C/C-ZrB_(2)-ZrC-SiC composites were respectively 68.9%and 29.7%lower than those of C/C-ZrC-SiC composites prepared by reactive melt infiltration.The ablation performance was improved because the volatilization of B_(2)O_(3),removes some of the heat,and the more uniformly distributed ZrO_(2),that helps produce a ZrO2-SiO2 continu-ous protective layer,hinders oxygen infiltration and decreases ablation.
基金supported by the National Natural Science Foundation of China(No.U19A2099)the Open Fund for Hubei Provincial Key Laboratory of Advanced Aerospace Power Technology,China(No.DLJJ2103007)the Hunan Graduate Research Innovation Project,China(No.CX20220097)。
文摘To obtain high-performance Zr-based ultra-high-temperature composites,Zr-based ultra-high-temperature gradient composites were prepared by changing the laying method of the infiltrant via reactive melt infiltration.The effects of different infiltrant laying methods on the microstructure and ablative properties of Zr-based ultrahigh-temperature gradient composites were investigated.The results showed that the gradient structure of the Zr-based ultrahigh-temperature gradient composites differed when the composition ratio of the infiltrant was changed.When the thicknesses of the Zr/Mo/Si layers were 6/4/12 mm and 8/2/12 mm,the SiMoZrC solid solution content in the samples increased and decreased along the infiltration direction,respectively.The gradient samples were ablated in an oxyacetylene flame at 3000°C for 40 s.The ablation resistance of the sample was the highest when the infiltrant was a powder and the thickness of the Zr/Mo/Si layer was 6/4/12 mm.
基金National Key R&D Program of China(2022YFB3707700)Shanghai Science and Technology Innovation Action Plan(21511104800)+3 种基金National Natural Science Foundation of China(52172111)National Science and Technology Major Project(2017-IV-0005-0042)Key Research Program of the Chinese Academy of Sciences(ZDRW-CN-2021-2-2)Science Center for Gas Turbine Project(P2022-B-IV-001-001)。
文摘ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2) and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2) phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2) oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2) is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2) particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2) increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2) in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZB
基金Project(51902239)supported by the National Natural Science Foundation of ChinaProject(2020JQ-808)supported by the Science and Technology Fund of Shaanxi Province,China+3 种基金Projects(19JK0400,19JK0402)supported by the Education Fund of Shaanxi Province,ChinaProject(SKLSP201752)supported by the State Key Laboratory of Solidification Processing in Northwestern Poly Technical University,ChinaProject(XAGDXJJ17008)supported by the Principal Fund of Xi’an Technological University,ChinaProject supported by the Youth Innovation Team of Shaanxi Universities,China。
文摘Particle erosion of C/C-SiC composites prepared by reactive melt infiltration with different Al addition was studied by gas-entrained solid particle impingement test.SEM,EDS and XRD were performed to analyze the composites before and after erosion.The results indicate that a U shape relationship curve presents between the erosion rates and Al content,and the lowest erosion rate occurs at 40 wt%Al.Except for the important influence of compactness,the increasing soft Al mixed with reactive SiC,namely the mixture located between carbon and residual Si also,plays a key role in the erosion of the C/C-SiC composites through crack deflection,plastic deformation and bonding cracked Si.
文摘BACKGROUND Reactive lymphoid hyperplasia(RLH)of the liver is a rare liver lesion.It is considered difficult to differentiate radiologically from hepatocellular carcinoma,metastatic liver tumor and other pathologies.CASE SUMMARY A 54-year-old woman presented to our hospital with RLH of the liver.The patient had a diagnosis of metastatic carcinoma of the liver from an unknown origin and subsequently underwent partial hepatectomy.However,histopathological analysis revealed RLH.The lesion showed perinodular enhancement in the arterial phase on contrast-enhanced computed tomography and magnetic resonance imaging.On diffusion-weighted imaging(DWI),we encountered linear hyperintensity along the portal tract consecutive to the liver lesion,which is a new characteristic radiologic finding.This finding corresponded to the lymphoid cell infiltration of the portal tract.Furthermore,there was strongly restricted diffusion on the apparent diffusion coefficient map.We used these characteristic radiologic findings to diagnose the lesion as a lymphoproliferative disease.CONCLUSION The linear hyperintensity consecutive to the liver lesion on DWI provided additional valuable diagnostic information.
基金supported by the National Natural Science Foundation of China(No.U19A2099)the CAS Key Laboratory of Carbon Materials,China(No.KLCMKFJJ2005)the Fund of Aerospace Research Institute of Material and Processing Technology,China(No.6142906200108).
文摘To investigate the thermal stability of ceramic-matrix composites,three kinds of C/C−ZrC−SiC composites with different Zr/Si molar ratios were synthesized by reactive melt infiltration.Employing region labeling method,the high-temperature thermal stability of the composites was systematically studied by changing the temperature and holding time of thermal treatment.Results show that the mass loss rate of low Si composites has a growth trend with increasing temperature,and a crystal transformation from β-SiC toα-SiC occurs in the composites.In the calibrated area,SiC phase experiences Ostwald ripening and volume change with location migration,while ZrC phase experiences a re-sintering process with diffusion.Moreover,it is found that increasing temperature has a more obvious effect on the thermal stability than extending holding time,which is mainly attributed to the faster diffusion rate of atoms.
基金Funded by the National Natural Science Foundation of China(Nos.52002003 and 52002098)Natural Science Foundation of Anhui Province,China(No.2008085QE196)Open Fund of Key Laboratory of Green Fabrication and Surface Technology of Advanced Metal Materials(Anhui University of Technology),Ministry of Education(No.GFST2020KF09)。
文摘ZrC_(x)-NbC_(y)-Cu composites were fabricated by pressure-less reactive infiltration of Zr-Cu binary melts into porous NbC preforms at 1300℃.The effect of Zr content in the infiltrator on microstructure of the as-synthesized composites was studied.Mechanical properties of the composites were reported.A partial displacement of Nb atoms in NbC by Zr atoms from Zr-Cu melt occurs during the reaction between Zr-Cu melt and porous NbC preform.The formation of a core-shell structure suggests the reaction is mainly a dissolutionprecipitation type.NbC dissolves into Zr-Cu melt,from which the(Nb,Zr)C_(z)phase precipitates and grows.With increasing Zr content in the Zr-Cu infiltrator,the reaction is enhanced and the infiltration is easily chocked.ZrC_(x)-NbC_(y)-Cu composite is synthesized using Zr_(14)Cu_(51)infiltrator.The flexural strength and fracture toughness of ZrC_(x)-NbC_(y)-Cu composite reach 637 MPa and 12.7 MPa·m^(1/2),respectively.And the improved toughness is probably attributed to residual Cu phase and plate-like Nb_(x)C_(y)phases.
文摘The reactive cast-infiltration technique was used to produce an Fe-WC surface composite layer on an iron casting, in which the WC particulates were formed in situ from a reaction of W with C. The structure and phase construction of the surface composite were evaluated by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDS), etc. An Fe-WC surface composite layer with a volume fraction of WC particles up to 30％ and particle size in the range 10～30 μm was successfully produced. Abrasive resistance test results show that the Fe-WC surface composite layer possesses great abrasive resistance.
文摘C/C-SiC composites have the potentiality to be applied in shield pumps of nuclear reactors as the bearing material because of their low density,good mechanical properties and excellent tribological properties.The C/C-SiC composites are fabricated via reactive melt infiltration(RMI)using silicon liquid infiltrated in C/C matrix composites.Friction and wear behaviors of C/C-SiC composites under water lubricated conditions are investigated using the block-on-ring test at room temperature,and compared with those of the resin graphite which is used as the bearing material in shield pumps at present.In addition,friction and wear mechanisms of C/C-SiC composites under water lubricated conditions have been discussed.Results show that tensile strengths of C/C-SiC composites are 150210 MPa,and compressive strengths are 403536 MPa.Friction and wear behaviors of C/C-SiC composites are closely related to the load and the speed.The time to reach a stable friction status decreases with the increase of the speed.Though the friction coefficient of C/C-SiC composites under water lubricated conditions is slightly higher than that of graphite,the wear rate of C/C-SiC composites is much lower,which suggests that the C/C-SiC composites can sustain a longer life during operation.
文摘Cobalt-silicon based carbon composites(Co–Si/C)have established a noteworthy consideration in recent years as a replacement for conventional materials in the automotive and aerospace industries.To achieve the composite,a reactive melt infiltration process(RMI)is used,in which a melt impregnates a porous preform by capillary force.This method promises a high-volume fraction of reinforcement and can be steered in such a way to get the good“near-net”shaped components.A mathematical model is developed using reaction-formed Co–Si alloy/C composite as a prototype system for this process.The wetting behavior and contact angle are discussed;surface tension and viscosity are calculated by Wang’s and Egry’s equations,respectively.Pore radii of 5μm and 10μm are set as a reference on highly oriented pyrolytic graphite.The graphs are plotted using the model,to study some aspects of the infiltration dynamics.This highlights the possible connections among the various processes.In this attempt,the Co–Si(62.5 at.%silicon)alloy’s maximum infiltration at 5μm and 10μm radii are found as 0.05668 m at 125 s and 0.22674 m at 250 s,respectively.
基金supported by the China Postdoctoral Science Foundation(No.2012M511752)the National Basic Research Program of China(No.2011CB605801)+2 种基金the Fundamental Research Funds for the Central Universities(No. 2012QNZT004)the Freedom Explore Program of Central South University,the Open-End Fund for the Valuable and Precision Instruments of Central South University(No.CSUZC2012026)the Postdoctoral Science Foundation of Central South University
文摘To meet the increasing demand for advanced materials capable of operation over 2000 ℃ for future thermal protection systems application, C/C-ZrC-SiC composites were fabricated by reactive melt infiltration （RMI） with Zr, Si mixed powders as raw materials. The structural evolution and formation mechanism of the C/C- ZrC-SiC composites were discussed, and the mechanical property of the as-prepared material was investigated by compression test. The results showed that after the RMI process, a special structure with ZrC-SiC multi-coating as outer layer and ZrC-SiC-PyC ceramics as inner matrix was formed. ZrC and SiC rich areas were formed in the composites and on the coating surface due to the formation of Zr-Si intermetallic compounds in the RMI process. Mechanical tests showed that the average compression strength of the C/C-ZrC-SiC composites was 133.86 MPa, and the carbon fibers in the composites were not seriously damaged after the RMI process.
