A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were st...A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD (X-ray diffraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.展开更多
C/C composites were prepared by chemical vapor infiltration(CVI),and then were subjected to Si,Zr,and MoSi_(2) reactive melt infiltration(RMI)to obtain C/C-SiC,C/C-SiC-ZrC,and C/C-SiC-ZrC-MoSi_(2) com-posites.The abla...C/C composites were prepared by chemical vapor infiltration(CVI),and then were subjected to Si,Zr,and MoSi_(2) reactive melt infiltration(RMI)to obtain C/C-SiC,C/C-SiC-ZrC,and C/C-SiC-ZrC-MoSi_(2) com-posites.The ablation behavior of these three composites was evaluated by high-energy CO 2 laser irra-diation.The surface temperature distribution of composite materials was simulated by finite element analysis.The results show that the ablation resistance mechanisms of the three materials are entirely different.The C/C-SiC-ZrC-MoSi_(2) com posite showed the best ablation performance among them.It is at-tributed to the lower oxygen permeability and richer heat dissipation mechanism of the C/C-SiC-ZrC-MoSi_(2) composite within the total temperature threshold.展开更多
Both high thermal conductivity(K)and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability.However,the drastic decrease of K values with the increased th...Both high thermal conductivity(K)and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability.However,the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications.In this work,graphite film with both large thickness and high K value is produced based on an in-situ com-position strategy between nanographene(G)and pyrocarbon(PyC)via chemical vapor deposition(CVD)using CH_(3) OH/C_(2)H_(5)OH mixed precursors.It’s found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites.Such G/PyC compos-ites can be completely graphitized at a lower temperature than the existing products.After 2400℃ an-nealing,dense,thick,and highly aligned graphite films were prepared.Their K values reach 1350 and 1010 W m^(-1) K^(-1) at the thickness of 40 and 120μm,respectively,surpassing the existing records with similar thicknesses.More importantly,the proposed method is insensitive to the deposition substrates,and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials.Besides,the G/PyC also exhibits better mechanical and electromagnetic shielding per-formances than the existing products,indicating a promising multifunctional application prospect.展开更多
As for the air plasma sprayed ZrB_(2)-based coatings,B content change caused by inevitable oxidation is predictable but commonly ignored.Affected by air plasma flame,the B element loss and residual B_(2) O_(3) in the ...As for the air plasma sprayed ZrB_(2)-based coatings,B content change caused by inevitable oxidation is predictable but commonly ignored.Affected by air plasma flame,the B element loss and residual B_(2) O_(3) in the sprayed ZrB_(2) coating were observed.Moreover,how the B content change affects the microstructure,phase evolution,and ablation resistance(2.4 MW/m^(2),60 s)of ZrB_(2)-based coatings with different sec-ondary phases(SiC,MoSi_(2),and TaC)was investigated.The B element loss contributed to the increase in surface temperature and the decline in the sintering degree of the ZrO_(2) layer.The evaporation of residual B_(2)O_(3) caused damage to the coating structure in the form of pores,whose negative effect was enhanced and reduced by MoSi_(2) and TaC secondary phases,respectively.This work will provide some insight into thermally sprayed non-oxide ceramic coatings in the atmosphere.展开更多
Polymer-derived ultra-high-temperature ceramic(UHTC)nanocomposites have attracted growing attention due to the increasing demands for advanced thermal structure components in aerospace.Herein,hafnium carbide(HfC)whisk...Polymer-derived ultra-high-temperature ceramic(UHTC)nanocomposites have attracted growing attention due to the increasing demands for advanced thermal structure components in aerospace.Herein,hafnium carbide(HfC)whiskers are successfully fabricated in carbon fiber preforms via the polymer-derived ceramic(PDC)method.A novel carbon nanotube(CNT)template growth mechanism combined with the PDC method is proposed in this work,which is different from the conventional vapor–liquid–solid(VLS)mechanism that is commonly used for polymer-derived nanostructured ceramics.The CNTs are synthesized and proved to be the templates for fabricating the HfC whiskers,which are generated by the released low-molecular-weight gas such as CO,CO_(2),and CH4 during the pyrolysis of a Hf-containing precursor.The formed products are composed of inner single crystal HfC whiskers that are measured to be several tens of micrometers in length and 100–200 nm in diameter and outer HfC/HfO_(2)particles.Our work not only proposes a new strategy to prepare the HfC whiskers,but also puts forward a new thinking of the efficient utilization of a UHTC polymer precursor.展开更多
C/C-SiC-HfC composites were fabricated by using Precursor Infiltration and Pyrolysis(PIP) combined with Gaseous Silicon Infiltration(GSI) process. Different GSI temperatures(1900 ℃ and 2100 ℃) were selected. The com...C/C-SiC-HfC composites were fabricated by using Precursor Infiltration and Pyrolysis(PIP) combined with Gaseous Silicon Infiltration(GSI) process. Different GSI temperatures(1900 ℃ and 2100 ℃) were selected. The combination of PIP and GSI could significantly reduce the preparation time of the composites. The morphology displaying a rich-Si layer was formed on the surface of the composites prepared at GSI 2100 ℃. Ablation performance of the composites was investigated by oxyacetylene torch. The results showed that after ablation for 120 s, compared to the composites prepared by PIP + 1900 ℃ GSI, the linear and mass ablation rates of the composites fabricated by PIP + 2100 ℃ GSI were decreased from 8.05 μm/s to 5.06 μm/s and from 1.61 mg/s to 1.03 mg/s, respectively. The coverage of the rich-Si surface layer promoted the generation of more SiO_(2) during ablation, which not only benefited for decreasing the surface temperature but also contributed to the formation of H-Si-O glass and the HfO_(2) skeleton, thus better resisting the denudation of the oxyacetylene torch.展开更多
Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The r...Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The repair agents were brushed on the defect areas and then underwent preoxidation(PR)or heat-treatment(HR)in a vacuum.The effects of different treatment processes on the chemical composition,microstructure of the repair agents,and the oxidation resistance behavior of the repaired coating were investigated.The repaired agents after both processes were pyrolyzed and generated SiOC ceramics,and they were well combined with the original coating.The thermal stability of PSO after preoxidation is poorer than that after heat-treatment,resulting in a weight loss rate of 5.88%after oxidation at 1500℃for 270 min,while that of the HR coating is only-0.87%,yet both have been great improvement compared with the unrepaired coating.This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.展开更多
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 ul...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.展开更多
Although in-situ growing carbon nanotubes (CNTs) on carbon fibers could greatly increase the matrix-dominated mechanical properties of carbon/carbon composites (C/Cs), it always decreased the tensile strength of c...Although in-situ growing carbon nanotubes (CNTs) on carbon fibers could greatly increase the matrix-dominated mechanical properties of carbon/carbon composites (C/Cs), it always decreased the tensile strength of carbon fibers. In this work, CNTs were introduced into unidirectional carbon fiber (CF) preforms by electrophoretic deposition (EPD) and they were used to reinforce C/Cs. Effects of the content of CNTs introduced by EPD on tensile property of unidirectional C/Cs were investigated. Results demonstrated that EPD could be used as a simple and efficient method to fabricate carbon nanotube reinforced C/Cs (CNT-C/Cs) with excellent tensile strength, which pays a meaningful way to maximize the global performance of CNT-C/Cs.展开更多
Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are ve...Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.展开更多
C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene fl...C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.展开更多
To improve the oxidation resistance of carbon/carbon (C/C) composites, mullite coating was prepared on the surface of SiC-coated C/C composites by supersonic plasma spraying. Phases and microstructures of mullite co...To improve the oxidation resistance of carbon/carbon (C/C) composites, mullite coating was prepared on the surface of SiC-coated C/C composites by supersonic plasma spraying. Phases and microstructures of mullite coating were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The coating primarily consists of a single phase of mullite (3AI203-2SIO2). The SEM results show that mullite coating was continuous and well bonded with the SiC inner layer without penetrating crack. Mullite coating exhibited good oxidation resistance, After 98.5 h oxidation at 1773 K and 9 thermal shock cycles between 1773 K and room temperature, the weight loss of the coated C/C composites was only 2.57%.展开更多
In order to improve ablation resistance of carbon/carbon(C/C) composites,SiC nanowires were prepared on C/C composites surface in prior through chemical vapor reaction before HfC coating.SiC nanowires grew randomly an...In order to improve ablation resistance of carbon/carbon(C/C) composites,SiC nanowires were prepared on C/C composites surface in prior through chemical vapor reaction before HfC coating.SiC nanowires grew randomly and had good combination with HfC coating.SiC nanowires toughed HfC coating had lower linear and mass ablation rates than original HfC coating.The surface was much flatter and exhibited smaller cracks in center region.The ablation mechanism of HfC coating has been changed by SiC nanowires.Thicker HfO2 fused layer was formed on the surface of the toughed HfC coating,which could provide efficient protection for C/C composites.Therefore,SiC nanowires toughed HfC coating behaved in better ablation resistance.展开更多
Nanocrystalline Hf B2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and Hf O2 as precursors within KCl/Na Cl molten salts.The results showed that the as-synthesized powders...Nanocrystalline Hf B2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and Hf O2 as precursors within KCl/Na Cl molten salts.The results showed that the as-synthesized powders exhibited an irregular polyhedral morphology with the average particle size of 155 nm and possessed a single-crystalline structure.From a fundamental aspect,we demonstrated the molten-salt assisted formation mechanism that the molten salts could accelerate the diffusion rate of the reactants and improve the chemical reaction rate of the reactants in the system to induce the synthesis of the high-purity nanocrystalline powders.Thermogravimetric analysis showed that the oxidation of the as-synthesized Hf B2 powders at 773–1073 K in air was the weight gain process and the corresponding oxidation behavior followed parabolic kinetics governed by the diffusion of oxygen in the oxide layer.展开更多
Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2(LMAS) was applied to join C/C-SiC composites and lithium aluminum si...Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2(LMAS) was applied to join C/C-SiC composites and lithium aluminum silicate(LAS) glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites(1.75 g/cm3) with a CVD-SiC coating to the C/C-SiC composites with a low density(1.48 g/cm3).The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.展开更多
Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as t...Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as the catalyst.The average diameters of SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires are about 145 nm,and the core-shell diameter ratios are about 0.41 and 0.53,respectively.The SiO_(2)shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself,respectively,based on the model analysis.The growth of these two nanowires conformed to the vapor-liquid-solid(VLS)mode.In this mode,CO played an important role in the growth of nanowires.There existed a critical partial pressure of CO(pC)determining the microstructure evolution of nanowires into whether SiC@SiO_(2)or Si@SiO_(2).The value of pC was calculated to be 4.01×10^(-15) Pa from the thermodynamic computation.Once the CO partial pressure in the system was greater than the pC,SiO tended to react with CO,causing the formation of SiC@SiO_(2)nanowires.However,the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO_(2)nanowires.This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.展开更多
C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of ...C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of the composites were analyzed by scanning electron microscopy and X-ray diffraction. The ablation resistance of the composites was evaluated under 3,000 °C oxyacetylene torch. After ablation for 120 s, the composites exhibit good ablation properties with the linear and mass ablation rates of 9.1 9 10-4mm/s and 1.30 9 10-3g/s, which are far lower than those of the C/C–SiC composites. The excellent ablative property of the C/C–SiC–HfC composites is resulted from the formation of HfO2 molten layer on the surface of the composites, which could play a positive role in reducing heat transfer and preventing oxygen transport to the underlying carbon substrate.展开更多
To improve the uniformity and the content of HfBin Hf B-Si-based ceramic coating and alleviate the damage of substrate,and then enhance the high-temperature(1700°C)oxidation and cyclic ablation resistances of car...To improve the uniformity and the content of HfBin Hf B-Si-based ceramic coating and alleviate the damage of substrate,and then enhance the high-temperature(1700°C)oxidation and cyclic ablation resistances of carbon/carbon composites,a close-knit double layer HfB_(2)-SiC/SiC coatings with a mosaic structure and high content of HfBwere prepared by a novel dipping-carbonization assisted pack cementation methods(DPC–HS/S).In contrast,a HfB_(2)-SiC/SiC coatings were also fabricated by pack cementation(PC–HS/S).Results revealed that the oxidation and ablation protective performances of the DPC–HS/S coatings were superior to those of PC–HS/S coatings.After 30 thermal cycles between 1500°C and room temperature,the mass gain of the coated sample was 0.78%,and the mass loss was 1.65%after oxidation at 1700°C for 156 h.Moreover,under an oxyacetylene torch ablation for 180 s(3 cycles),the linear ablation rate of the DPC–HS/S coated specimen was 1.62μm/s,which was much lower than that of PC–HS/S coated specimen(3.08μm/s).展开更多
Ablation resistance of monolithic LaB-doped ZrC coating for SiC-coated carbon/carbon composites by supersonic atmospheric plasma spray was investigated under an oxyacetylene torch with a heat flux of 4.18 MW/m~2. Resu...Ablation resistance of monolithic LaB-doped ZrC coating for SiC-coated carbon/carbon composites by supersonic atmospheric plasma spray was investigated under an oxyacetylene torch with a heat flux of 4.18 MW/m~2. Result shows that ZrC coating with 10 vol.% LaBhas a good ablation resistance compared with pure ZrC, ZrC with 20 vol.% LaBand SiC-doped ZrC coating. After ablation for 15 s, the weight is increased by 1.12 mg/s. The good ablation resistance is ascribed to the formation of a stabilized scale which consists of protective LaZrO-containing molten phase and ZrOparticles keeping the integrity of the coating.展开更多
基金supported by the National "973"Project under grant No. 2006CB600908
文摘A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD (X-ray diffraction), SEM (scanning electron microscopy), and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.
文摘C/C composites were prepared by chemical vapor infiltration(CVI),and then were subjected to Si,Zr,and MoSi_(2) reactive melt infiltration(RMI)to obtain C/C-SiC,C/C-SiC-ZrC,and C/C-SiC-ZrC-MoSi_(2) com-posites.The ablation behavior of these three composites was evaluated by high-energy CO 2 laser irra-diation.The surface temperature distribution of composite materials was simulated by finite element analysis.The results show that the ablation resistance mechanisms of the three materials are entirely different.The C/C-SiC-ZrC-MoSi_(2) com posite showed the best ablation performance among them.It is at-tributed to the lower oxygen permeability and richer heat dissipation mechanism of the C/C-SiC-ZrC-MoSi_(2) composite within the total temperature threshold.
基金financially supported by the National Natu-ral Science Foundation of China(Nos.51872234,52222204,and 52002322)the Natural Science Basic Research Plan in Shaanxi(No.2020JQ-154)+1 种基金the Key R&D Program of Shaanxi Province(No.2019ZDLGY04-02)the China Postdoctoral Science Foundation(No.2020M683556).
文摘Both high thermal conductivity(K)and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability.However,the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications.In this work,graphite film with both large thickness and high K value is produced based on an in-situ com-position strategy between nanographene(G)and pyrocarbon(PyC)via chemical vapor deposition(CVD)using CH_(3) OH/C_(2)H_(5)OH mixed precursors.It’s found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites.Such G/PyC compos-ites can be completely graphitized at a lower temperature than the existing products.After 2400℃ an-nealing,dense,thick,and highly aligned graphite films were prepared.Their K values reach 1350 and 1010 W m^(-1) K^(-1) at the thickness of 40 and 120μm,respectively,surpassing the existing records with similar thicknesses.More importantly,the proposed method is insensitive to the deposition substrates,and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials.Besides,the G/PyC also exhibits better mechanical and electromagnetic shielding per-formances than the existing products,indicating a promising multifunctional application prospect.
基金supported by the National Key R&D Program of China(No.2021YFA0715800)the Science Center for Gas Turbine Project(No.P2021-A-IV-003-001)+1 种基金the National Nat-ural Science Foundation of China(No.52125203)the Innova-tion Foundation for Doctor Dissertation of Northwestern Polytech-nical University(No.CX2021007)。
文摘As for the air plasma sprayed ZrB_(2)-based coatings,B content change caused by inevitable oxidation is predictable but commonly ignored.Affected by air plasma flame,the B element loss and residual B_(2) O_(3) in the sprayed ZrB_(2) coating were observed.Moreover,how the B content change affects the microstructure,phase evolution,and ablation resistance(2.4 MW/m^(2),60 s)of ZrB_(2)-based coatings with different sec-ondary phases(SiC,MoSi_(2),and TaC)was investigated.The B element loss contributed to the increase in surface temperature and the decline in the sintering degree of the ZrO_(2) layer.The evaporation of residual B_(2)O_(3) caused damage to the coating structure in the form of pores,whose negative effect was enhanced and reduced by MoSi_(2) and TaC secondary phases,respectively.This work will provide some insight into thermally sprayed non-oxide ceramic coatings in the atmosphere.
基金supported by the National Natural Science Foundation of China(Grant Nos.52293373,52130205,and 52061135102)the National Key R&D Program of China(Grant No.2021YFA0715803).Also,we would like to thank ND Basic Research Funds of Northwestern Polytechnical University(Grant No.G2022WD)and China Scholarship Program,2020(Grant No.202006290179).
文摘Polymer-derived ultra-high-temperature ceramic(UHTC)nanocomposites have attracted growing attention due to the increasing demands for advanced thermal structure components in aerospace.Herein,hafnium carbide(HfC)whiskers are successfully fabricated in carbon fiber preforms via the polymer-derived ceramic(PDC)method.A novel carbon nanotube(CNT)template growth mechanism combined with the PDC method is proposed in this work,which is different from the conventional vapor–liquid–solid(VLS)mechanism that is commonly used for polymer-derived nanostructured ceramics.The CNTs are synthesized and proved to be the templates for fabricating the HfC whiskers,which are generated by the released low-molecular-weight gas such as CO,CO_(2),and CH4 during the pyrolysis of a Hf-containing precursor.The formed products are composed of inner single crystal HfC whiskers that are measured to be several tens of micrometers in length and 100–200 nm in diameter and outer HfC/HfO_(2)particles.Our work not only proposes a new strategy to prepare the HfC whiskers,but also puts forward a new thinking of the efficient utilization of a UHTC polymer precursor.
基金supported by the National Key Research and Development Program of China(No.2021YFA0715803)the Science Center for Gas Turbine Project,China(No.P2021A-Ⅳ-003-001)+2 种基金the National Natural Science Foundation of China(52002321)the Fundamental Research Funds for the Central Universities,China(No.G2022KY0609)the Young Talent Program of Association for Science and Technology in Xi’an,China(No.095920211338).
文摘C/C-SiC-HfC composites were fabricated by using Precursor Infiltration and Pyrolysis(PIP) combined with Gaseous Silicon Infiltration(GSI) process. Different GSI temperatures(1900 ℃ and 2100 ℃) were selected. The combination of PIP and GSI could significantly reduce the preparation time of the composites. The morphology displaying a rich-Si layer was formed on the surface of the composites prepared at GSI 2100 ℃. Ablation performance of the composites was investigated by oxyacetylene torch. The results showed that after ablation for 120 s, compared to the composites prepared by PIP + 1900 ℃ GSI, the linear and mass ablation rates of the composites fabricated by PIP + 2100 ℃ GSI were decreased from 8.05 μm/s to 5.06 μm/s and from 1.61 mg/s to 1.03 mg/s, respectively. The coverage of the rich-Si surface layer promoted the generation of more SiO_(2) during ablation, which not only benefited for decreasing the surface temperature but also contributed to the formation of H-Si-O glass and the HfO_(2) skeleton, thus better resisting the denudation of the oxyacetylene torch.
基金supported by the National Key R&D Program of China(2021YFA0715800,2021YFA0715803)Science Center for Gas Turbine Project(P2021-A-IV-003-001)National Natural Science Foundation of China(52125203,52130205,52002321).
文摘Polysiloxane(PSO)was adopted as the matrix of the repair agents,and SiCeZrB_(2)powder was used as the filler,to repair the prefabricated defects on the SiCeZrB_(2)/SiC(SZS)coating of carbon/carbon(C/C)composites.The repair agents were brushed on the defect areas and then underwent preoxidation(PR)or heat-treatment(HR)in a vacuum.The effects of different treatment processes on the chemical composition,microstructure of the repair agents,and the oxidation resistance behavior of the repaired coating were investigated.The repaired agents after both processes were pyrolyzed and generated SiOC ceramics,and they were well combined with the original coating.The thermal stability of PSO after preoxidation is poorer than that after heat-treatment,resulting in a weight loss rate of 5.88%after oxidation at 1500℃for 270 min,while that of the HR coating is only-0.87%,yet both have been great improvement compared with the unrepaired coating.This work provides an effective and simple approach to repairing damaged coatings for high-temperature applications.
基金support from the National Natural Science Foundation of China(52032001,52022072,52032003,51972243,92060202,51872239,51872059,51772061,52061135102,52002321,50632070,51272266,and 52102093)bilateral project of NSFC-JSPS(51111140017 and 51611140121)+4 种基金China Postdoctoral Science Foundation(2021M690817)Fundamental Research Funds for the Central Universities(G2020KY05125)Key Research Program of Frontier Sciences,CAS(QYZDY-SSW-JSC031)the projects supported by fee State Key Laboratory of Advanced Technology for Materials Synthesis and Processing,Wuhan University of Technology(2021-KF-5)fee State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,Donghua University(KF2116)are greatly acknowledged.
文摘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.
基金supported by the Program of Introducing Talents of Discipline to Universities(No.B08040)the Ph.D Thesis Innovation Fund of NWPU(No.cx201214)+1 种基金the Key Grant Proiect of Chinese Ministry of Education(No.313047)the National Natural Science Foundation of China(Nos. 51275417.50832004 and 51202194)
文摘Although in-situ growing carbon nanotubes (CNTs) on carbon fibers could greatly increase the matrix-dominated mechanical properties of carbon/carbon composites (C/Cs), it always decreased the tensile strength of carbon fibers. In this work, CNTs were introduced into unidirectional carbon fiber (CF) preforms by electrophoretic deposition (EPD) and they were used to reinforce C/Cs. Effects of the content of CNTs introduced by EPD on tensile property of unidirectional C/Cs were investigated. Results demonstrated that EPD could be used as a simple and efficient method to fabricate carbon nanotube reinforced C/Cs (CNT-C/Cs) with excellent tensile strength, which pays a meaningful way to maximize the global performance of CNT-C/Cs.
基金supported by the National Natural Science Foundation of China(Nos.91860203,51821091,51872239,52002321 and 52061135102)the China Postdoctoral Science Foundation(No.2019M660265)+3 种基金the Fundamental Research Funds for the Central Universities(China,Nos.G2019KY05116,G2020KY05125)the Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD003)the Creative Research Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(Nos.614291102010517,5050200015 and 5150200033)the Shaanxi Provincial Education Department of China(No.2020JQ-170)。
文摘Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51221001 and 51272213)the Foundation for the Author of National Excellent Doctoral Dissertation of China 201036+1 种基金the Research Fund of State Key Laboratory of Solidification Processing (NWPU), China (Grant No. 25-TZ-2009)the "111" Project (Grant No. B08040)
文摘C/C-ZrC composites with continuous ZrC matrix were prepared by precursor infiltration and pyrolysis process using zirconium-containing polymer.Ablation properties of the composites were investigated by oxyacetylene flame with heat flux of 2380 and 4180 kW/m2,respectively.The results showed that C/C-ZrC composites exhibited excellent ablation resistance under the heat flux of 2380 kW/m2for 120 s and a tree-coral-like ZrO2protective layer formed after ablation.However,when the heat flux increased to 4180 kW/m2,the maximum temperature of ablated surface reached 2500 ℃ and a strong degradation of ablation resistance was observed due to the weak bonding between the formed ZrO2layer and the composites.The flexural strength of C/C-ZrC composites was 110.7 ± 7.5 MPa.There were a large number of carbon fiber bundles pull-out,and the composites exhibited a pseudo-plastic fracture behavior.
基金supported by the National Natural Science Foundation of China under Grant No. 51072166 and No.50902111the "111" Project under Grant No.D08040NPU Foundation for Fundamental Research and the Research Fund of the State Key Laboratory of Solidification Processing(NWPU), China (Grant No.73-QP-2010)
文摘To improve the oxidation resistance of carbon/carbon (C/C) composites, mullite coating was prepared on the surface of SiC-coated C/C composites by supersonic plasma spraying. Phases and microstructures of mullite coating were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The coating primarily consists of a single phase of mullite (3AI203-2SIO2). The SEM results show that mullite coating was continuous and well bonded with the SiC inner layer without penetrating crack. Mullite coating exhibited good oxidation resistance, After 98.5 h oxidation at 1773 K and 9 thermal shock cycles between 1773 K and room temperature, the weight loss of the coated C/C composites was only 2.57%.
基金supported by National Natural Science Foundation of China (No. 51072166)National Science Foundation of China, (No. 51221001)+1 种基金Program for New Century Excellent Talents in Universitythe "111 Project" (No. B08040)
文摘In order to improve ablation resistance of carbon/carbon(C/C) composites,SiC nanowires were prepared on C/C composites surface in prior through chemical vapor reaction before HfC coating.SiC nanowires grew randomly and had good combination with HfC coating.SiC nanowires toughed HfC coating had lower linear and mass ablation rates than original HfC coating.The surface was much flatter and exhibited smaller cracks in center region.The ablation mechanism of HfC coating has been changed by SiC nanowires.Thicker HfO2 fused layer was formed on the surface of the toughed HfC coating,which could provide efficient protection for C/C composites.Therefore,SiC nanowires toughed HfC coating behaved in better ablation resistance.
基金financial support from the National Key R&D Program of China (No. 2017YFB0703200)National Natural Science Foundation of China (Nos. 51802100 and 51972116)+1 种基金Young Elite Scientists Sponsorship Program by CAST (No. 2017QNRC001)the fund of the State Key Laboratory of Solidification Processing in NWPU (No. SKLSP201820)
文摘Nanocrystalline Hf B2 powders were successfully synthesized by molten salt synthesis technique at 1373 K using B and Hf O2 as precursors within KCl/Na Cl molten salts.The results showed that the as-synthesized powders exhibited an irregular polyhedral morphology with the average particle size of 155 nm and possessed a single-crystalline structure.From a fundamental aspect,we demonstrated the molten-salt assisted formation mechanism that the molten salts could accelerate the diffusion rate of the reactants and improve the chemical reaction rate of the reactants in the system to induce the synthesis of the high-purity nanocrystalline powders.Thermogravimetric analysis showed that the oxidation of the as-synthesized Hf B2 powders at 773–1073 K in air was the weight gain process and the corresponding oxidation behavior followed parabolic kinetics governed by the diffusion of oxygen in the oxide layer.
基金funding supported from the National Natural Science Foundation of China(Grant Nos.51221001 and 51222207)the "111" Project(Grant No.B08040)the Foundation of the National Excellent Doctoral Dissertation of China(No.201036)
文摘Porous C/C-SiC composites were prepared through a two-step chemical vapor infiltration process,and a multi-interlayer joint of Li20-MgO-Al2O3-SiO2(LMAS) was applied to join C/C-SiC composites and lithium aluminum silicate(LAS) glass ceramics by means of a vacuum hot-pressing technique.Plenty of SiC whiskers were generated in the pores of low-density C/C composites during chemical vapor deposition process,which is essentia! to form a zigzag interface structure between C/C-SiC substrate and the LMAS interlayer.The average shear strength of the LMAS joint was improved from 12.17 to 19.91 MPa after changing the composites from high-density C/C composites(1.75 g/cm3) with a CVD-SiC coating to the C/C-SiC composites with a low density(1.48 g/cm3).The improvement of the joint strength is mainly attributed to the formation of the inlay structure at the SiC-C/C and SiC-LMAS interfaces.
基金This work was supported by the National Natural Science Foundation of China(Nos.52061135102,52101098)Innovation Talent Promotion Plan of Shaanxi Province for Science and Technology Innovation Team(No.2020TD-003)+2 种基金Young Talents for Science and Technology Association supported by Shaanxi Province(No.20200406)the Fund of Key Laboratory of National Defense Science and Technology in Northwestern Polytechnical University(No.JCKYS2020607003)Innovation and Entrepreneurship Training Program for College Students(No.202110699088).
文摘Core-shell structured SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires were prepared on the surface of carbon/carbon(C/C)composites by a thermal evaporation method using SiO powders as the silicon source and Ni(NO3)2 as the catalyst.The average diameters of SiC@SiO_(2)nanowires and Si@SiO_(2)nanowires are about 145 nm,and the core-shell diameter ratios are about 0.41 and 0.53,respectively.The SiO_(2)shells of such two nanowires resulted from the reaction between SiO and CO and the reaction of SiO itself,respectively,based on the model analysis.The growth of these two nanowires conformed to the vapor-liquid-solid(VLS)mode.In this mode,CO played an important role in the growth of nanowires.There existed a critical partial pressure of CO(pC)determining the microstructure evolution of nanowires into whether SiC@SiO_(2)or Si@SiO_(2).The value of pC was calculated to be 4.01×10^(-15) Pa from the thermodynamic computation.Once the CO partial pressure in the system was greater than the pC,SiO tended to react with CO,causing the formation of SiC@SiO_(2)nanowires.However,the decomposition of SiO played a predominant role and the products mainly consisted of Si@SiO_(2)nanowires.This work may be helpful for the regulation of the growth process and the understanding of the growth mechanism of silicon-based nanowires.
基金financially supported by the National Natural Science Foundation of China(Nos.51221001 and 51272213)the Author of National Excellent Doctoral Dissertation of China(No.201036),the ‘‘111’’ project of China (No.B08040)National Basic Research program of China (No.2011CB605806)
文摘C/C–SiC–HfC composites were fabricated via precursor infiltration and pyrolysis using a mixture solution of organic hafnium-containing polymer and polycarbosilane as precursor. The microstructures and the phases of the composites were analyzed by scanning electron microscopy and X-ray diffraction. The ablation resistance of the composites was evaluated under 3,000 °C oxyacetylene torch. After ablation for 120 s, the composites exhibit good ablation properties with the linear and mass ablation rates of 9.1 9 10-4mm/s and 1.30 9 10-3g/s, which are far lower than those of the C/C–SiC composites. The excellent ablative property of the C/C–SiC–HfC composites is resulted from the formation of HfO2 molten layer on the surface of the composites, which could play a positive role in reducing heat transfer and preventing oxygen transport to the underlying carbon substrate.
基金financially supported by the National Natural Science Foundation of China(Nos.51872239,52061135102,52002321)the Creative Research Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(No.5050200015)+1 种基金the Fundamental Research Funds for the Central Universities(No.G2020KY05125)the Xi’an Association for Science and Technology"Young Talent Support Project"(No.095920211338)。
文摘To improve the uniformity and the content of HfBin Hf B-Si-based ceramic coating and alleviate the damage of substrate,and then enhance the high-temperature(1700°C)oxidation and cyclic ablation resistances of carbon/carbon composites,a close-knit double layer HfB_(2)-SiC/SiC coatings with a mosaic structure and high content of HfBwere prepared by a novel dipping-carbonization assisted pack cementation methods(DPC–HS/S).In contrast,a HfB_(2)-SiC/SiC coatings were also fabricated by pack cementation(PC–HS/S).Results revealed that the oxidation and ablation protective performances of the DPC–HS/S coatings were superior to those of PC–HS/S coatings.After 30 thermal cycles between 1500°C and room temperature,the mass gain of the coated sample was 0.78%,and the mass loss was 1.65%after oxidation at 1700°C for 156 h.Moreover,under an oxyacetylene torch ablation for 180 s(3 cycles),the linear ablation rate of the DPC–HS/S coated specimen was 1.62μm/s,which was much lower than that of PC–HS/S coated specimen(3.08μm/s).
基金supported by the National Natural Science Foundation of China (Nos. 51521061,51502245,51472203)the "111" Project (Grant no. B08040)the Research Fund of State Key Laboratory of Solidification Processing (NWPU),China (Grant No.142-TZ-2016)
文摘Ablation resistance of monolithic LaB-doped ZrC coating for SiC-coated carbon/carbon composites by supersonic atmospheric plasma spray was investigated under an oxyacetylene torch with a heat flux of 4.18 MW/m~2. Result shows that ZrC coating with 10 vol.% LaBhas a good ablation resistance compared with pure ZrC, ZrC with 20 vol.% LaBand SiC-doped ZrC coating. After ablation for 15 s, the weight is increased by 1.12 mg/s. The good ablation resistance is ascribed to the formation of a stabilized scale which consists of protective LaZrO-containing molten phase and ZrOparticles keeping the integrity of the coating.