Ultra-high temperature ceramics(UHTCs)exhibit a unique combination of excellent properties,including ultra-high melting point,excellent chemical stability,and good oxidation resistance,which make them promising candid...Ultra-high temperature ceramics(UHTCs)exhibit a unique combination of excellent properties,including ultra-high melting point,excellent chemical stability,and good oxidation resistance,which make them promising candidates for aerospace and nuclear applications.However,the degradation of hightemperature strength is one of the main limitations for their ultra-high temperature applications.Thus,searching for mechanisms that can help to develop high-performance UHTCs with good high-temperature mechanical properties is urgently needed.To achieve this goal,grain boundary segregation of a series of carbides,including conventional,medium entropy,and high entropy transition metal carbides,i.e.,Zr_(0.95)W_(0.05)C,TiZrHfC_(3),ZrHfNbTaC_(4),TiZrHfNbTaC_(5),were studied by atomistic simulations with a fitted Deep Potential(DP),and the effects of segregation on grain boundary strength were emphasized.For all the studied carbides,grain boundary segregations are realized,which are dominated by the atomic size effect.In addition,tensile simulations indicate that grain boundaries(GBs)will usually be strengthened due to segregation.Our simulation results reveal that grain boundary segregation may be a universal mechanism in enhancing the high-temperature strength of both conventional UHTCs and medium/high entropy UHTCs,since GBs play a key role in controlling the fracture of UHTCs at elevated temperatures.展开更多
A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics ...A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics (UHTCs) in aerospace engineering. The composite is pre-oxidized at temperatures of 900 ℃ and 1100 ℃ for 1 h and 3 h in air. A theoretical model considering surface heat transfer has been given and analyzed. A water-quenching technique is adopted at different temperatures from 300 ℃ to 600 ℃ in order to investigate the thermal shock behavior of pre-oxidized composites. The critical thermal shock temperature improves more than 40% after pre-oxidizing at 1100 ℃ for 3 h. However,the composites strength is not improved as a result of the insensitivity to surface defects.展开更多
The strong covalent bonding characters of zirconium diboride（ Zr B2） and hafnium diboride（ Hf B2） with natural hexagonal Al B2-type crystal structure give them high melting points（ 〉 3 200 ℃）, high bending str...The strong covalent bonding characters of zirconium diboride（ Zr B2） and hafnium diboride（ Hf B2） with natural hexagonal Al B2-type crystal structure give them high melting points（ 〉 3 200 ℃）, high bending strength, high elastic modulus and high hardness.Zr B2- and Hf B2-based ceramics are promising candidates for the thermal protection components of propulsion systems,rocket nozzles,sharp leading edges and nose cones. This paper introduces the recent research progress on Zr B2- and Hf B2-based ceramics,including the synthesis methods of the boride powders,the sintering methods of the boride-based ceramics and their properties.The advantages of different synthesis methods and sintering methods are compared. The influence factors on the mechanical properties,oxidation resistance and thermal shock resistance are summarized.展开更多
Urban human thermal comfort(UHTC) is affected for interacting of weather condition and underlying surface framework of urban area. Urban underlying surface temperature value and Normalized Difference Vegetation Index(...Urban human thermal comfort(UHTC) is affected for interacting of weather condition and underlying surface framework of urban area. Urban underlying surface temperature value and Normalized Difference Vegetation Index(NDVI) were calculated using image interpreting and supervised classification technique by ERDAS IMAGE software using 1991 and 1999 Landsat TM images data. Reference to the relational standard of assessing human thermal comfort and other meteorology data of Hangzhou City in summer, air temperature and relative humidity variation of different land types of underlying surface were inversed. By choosing discomfort index as an indictor, the spatial distribution characteristic and the spatial variation degree of UHTC were estimated and mapped on a middle scale, that is, in six districts of Hangzhou. The main characteristics of UHTC spatial variation from 1991 to 1999 were revealed using a GIS-based calculation model. The variation mechanism were analyzed and discussed from the viewpoint of city planning, construction and environmental protection.展开更多
ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinabil...ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinability and excellent oxidation/ablation resistance in the extreme harsh environment. The struts were machined with electrospark wire-electrode cutting techniques to form UHTC into the desired shape, and with laser drilling to drill tiny holes providing the channels for fuel injection. The integrated thermal-structural characteristic of the struts was evaluated in high-temperature combustion environment by the propane-oxygen free jet facility, subject to the heat flux of 1.5 MW/m^2 lasting for 300 seconds, and the struts maintained integrity during and after the first experiment. The experiments were repeated for verifying the reusability of the struts. Fracture occurred during the second repeated experiment with the crack propagating through the hole. Finite element analysis（FEA） was carried out to study the thermal stress distribution in the UHTC strut. The simulation results show a high thermal stress concentration occurs at the hole which is the crack initiation position. The phenomenon is in good agreement with the experimental results. The study shows that the thermal stress concentration is a practical key issue in the applications of the reusable UHTC strut for fuel injection structure in scramjets.展开更多
The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TS...The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.展开更多
Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Z...Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Zr,Hf)-containing single-source precursors(SSPs),followed by spark plasma sintering(SPS).A thorough characterization was conducted to elucidate the synthesis of the SSPs,polymer-to-ceramic transformation,chemical/phase compositions,and microstructure of the SiTiZrHfC-based ceramics.The results revealed the feasibility of synthesizing nanocomposites with high(Ti,Zr,Hf)C contents using the SSP method.These nanocomposites were characterized by a unique microstructure with in situ generated(Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed withβ-SiC.The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s.Impressively,the nanocomposites exhibited excellent ablation resistance,and the lowest linear ablation rate reached−0.58μm/s at 2200°C.Notably,the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the(Ti,Zr,Hf)C phase via the molecular design of the SSPs.The formation of a multiple-oxide layer with both a high-meltingpoint phase((Ti,Zr,Hf)O_(2))and low-melting-point phases((Zr,Hf)TiO_(4))and glassy SiO_(2),as well as their structure,played a critical role in the enhanced ablation resistance.The uniform distribution of the high-melting-point(Ti,Zr,Hf)O_(2)nano/microparticles throughout the glassy SiO_(2)matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect,offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.展开更多
Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed l...Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.展开更多
A new additive technique for manufacturing of short fibre-reinforced ultra-refractory ceramics is presented.This technique allows the fabrication of solvent-free,thin(~100µm),flexible,and easy-to-handle sheets su...A new additive technique for manufacturing of short fibre-reinforced ultra-refractory ceramics is presented.This technique allows the fabrication of solvent-free,thin(~100µm),flexible,and easy-to-handle sheets suitable for fabricating homogeneous or layered structures.A large range of compositions,in terms of matrix and fibre volumetric contents,from 0%to 100%is possible.The amount of short carbon fibres incorporated in the sheets ranged from 20 to 50 vol%,whereas the fibre length ranged from 3 to 5 mm.The matrix composition investigated with this technique consisted of ZrB_(2)/SiC/Y_(2)O_(3).By increasing the fibre amount from 35 to 50 vol%,an improvement of mechanical properties was observed.Four-point flexural strength(σ)ranged from 107 to 140 MPa,depending on the amount of carbon fibres(Cf).The same holds true for the work of fracture,ranging from 108 to 253 J/m^(2).Functionally graded composites were fabricated by overlapping sheets with a fibre gradient(0%-50%).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
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
Spiral fibers were considered to be an ideal toughening phase of ultra-high torsional release effect.In this work,ZrB_(2)(Z)-20 vol%SiC(S)spiral fiber(ZS_(sf))with controllable structure was prepared by a combination ...Spiral fibers were considered to be an ideal toughening phase of ultra-high torsional release effect.In this work,ZrB_(2)(Z)-20 vol%SiC(S)spiral fiber(ZS_(sf))with controllable structure was prepared by a combination approach of liquid rope effect and non-solvent-induced phase separation.Dominantly depended on the kinematic viscosity(η),dropping height(H),and flow rate(Q),the geometric parameters of ZS_(sf) involving filament diameter(d)and coil diameter(D)were followed the relationship of d≈0.516×10^(-3) Q^(1/2)H^(−1/4) and D≈0.25×10^(-3)(Q/H)^(1/3),respectively,within the optimizedηof 10-15 Pa·s.Three different microstructures of ZS_(sf) were achieved by adjusting the polymer/solvent/non-solvent system assisted with phase diagram calculation,including dense,hollow,and hierarchical pore structures.The ZrB_(2)-SiC with 1 wt%ZS_(sf) composites prepared by hot isostatic pressing(HIP)exhibited a~30%increase in fracture toughness(KIC,4.41 MPa·m^(1/2))compared with the ZrB_(2)-SiC composite,where the microscopic fracture toughness of the ZS_(sf) was~80%higher than that of the matrix.The fibers with a~10 nm in-situ-synthesized graphite phase amongst grain boundaries of ZrB_(2) and SiC changed the fracture mode,and promoted the crack deflection and pull-out adjacent the interface of matrix and the fiber.展开更多
Ultra-high-temperature ceramic matrix composites(UHTCMCs)based on a ZrB_(2)/SiC matrix have been investigated for the fabrication of reusable nozzles for propulsion.Three de Laval nozzle prototypes,obtained by sinteri...Ultra-high-temperature ceramic matrix composites(UHTCMCs)based on a ZrB_(2)/SiC matrix have been investigated for the fabrication of reusable nozzles for propulsion.Three de Laval nozzle prototypes,obtained by sintering with either hot pressing(HP)or spark plasma sintering(SPS),were tested 2-3 times in a hybrid rocket motor for proving reusability.Sections were extracted after oxidation tests to study the microstructural changes and oxidative and thermomechanical stresses induced by the repeated tests.Compared to a reference graphite nozzle,no measurable erosion was observed for the UHTCMC-based nozzles.The oxidation mechanism consisted in the formation of a ZrO_(2)intermediate layer,with a liquid silicon oxide(SiO_(2))layer on the surface that was displaced by the action of the gas flux towards the divergent part of the nozzle,protecting it from further oxidation.Both specimens obtained by HP and SPS displayed similar performance,with very slight differences,which were attributed to small changes in porosity.These tests demonstrated the capability of complex-shaped prototypes made of the developed UHTCMCs to survive repeated exposure to environments representative of a realistic space propulsion application,for overall operating time up to 30 s,without any failure nor measurable erosion,making a promising step towards the development of reusable rocket components.展开更多
Multicomponent boron-containing carbide coatings(i.e.,(Zr,Ti)C_(x)B_(y))on a C/C composite show good ablation resistance.However,the high-temperature oxidation behavior of this new type of boron-containing(Zr,Ti)C_(x)...Multicomponent boron-containing carbide coatings(i.e.,(Zr,Ti)C_(x)B_(y))on a C/C composite show good ablation resistance.However,the high-temperature oxidation behavior of this new type of boron-containing(Zr,Ti)C_(x)B_(y)solid solution ceramics has not been clarified yet.The present work fabricated(Zr,Ti)C_(x)B_(y)solid solution block ceramics by spark plasma sintering,and their oxidation behavior at 1600℃in air(N2–20-vol%O2)was investigated for the first time.The effects of boron on the oxidation resistance of(Zr,Ti)C_(x)B_(y)ceramics were examined.The results indicate that the(Zr,Ti)C_(x)B_(y)ceramics display good oxidation resistance with the parabolic rate law describing the oxidation process.After the trace solution of boron(0.5 wt%)into(Zr,Ti)Cx,the oxidation resistance of carbide ceramics is significantly enhanced,leading to a decrease of 30%in the oxidation rate constant.The formed oxide scale in the(Zr,Ti)C_(x)B_(y)ceramics is dense,and the interlayer shows stronger ability to inhibit inward diffusion of oxygen.In addition,the introduction of boron leads to more negative binding energy of(Zr,Ti)C_(x)B_(y)and improves the oxidation resistance of carbides.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
基金supported by the National Natural Science Foundation of China(No.51672064)。
文摘Ultra-high temperature ceramics(UHTCs)exhibit a unique combination of excellent properties,including ultra-high melting point,excellent chemical stability,and good oxidation resistance,which make them promising candidates for aerospace and nuclear applications.However,the degradation of hightemperature strength is one of the main limitations for their ultra-high temperature applications.Thus,searching for mechanisms that can help to develop high-performance UHTCs with good high-temperature mechanical properties is urgently needed.To achieve this goal,grain boundary segregation of a series of carbides,including conventional,medium entropy,and high entropy transition metal carbides,i.e.,Zr_(0.95)W_(0.05)C,TiZrHfC_(3),ZrHfNbTaC_(4),TiZrHfNbTaC_(5),were studied by atomistic simulations with a fitted Deep Potential(DP),and the effects of segregation on grain boundary strength were emphasized.For all the studied carbides,grain boundary segregations are realized,which are dominated by the atomic size effect.In addition,tensile simulations indicate that grain boundaries(GBs)will usually be strengthened due to segregation.Our simulation results reveal that grain boundary segregation may be a universal mechanism in enhancing the high-temperature strength of both conventional UHTCs and medium/high entropy UHTCs,since GBs play a key role in controlling the fracture of UHTCs at elevated temperatures.
基金Sponsored by the National Natural Science Foundation of China ( Grant No.10572044,90505015)the Program for New Century Excellent Talents in University (Grant No.NCET-05-0346)
文摘A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics (UHTCs) in aerospace engineering. The composite is pre-oxidized at temperatures of 900 ℃ and 1100 ℃ for 1 h and 3 h in air. A theoretical model considering surface heat transfer has been given and analyzed. A water-quenching technique is adopted at different temperatures from 300 ℃ to 600 ℃ in order to investigate the thermal shock behavior of pre-oxidized composites. The critical thermal shock temperature improves more than 40% after pre-oxidizing at 1100 ℃ for 3 h. However,the composites strength is not improved as a result of the insensitivity to surface defects.
基金Financial supports from the National Natural Science Foundation of China ( No. 51272266 )the Science and Technology Commission of Shanghai ( No. 15ZR1445200 )the State Key Laboratory of High Performance Ceramics and Superfine Microstructure
文摘The strong covalent bonding characters of zirconium diboride（ Zr B2） and hafnium diboride（ Hf B2） with natural hexagonal Al B2-type crystal structure give them high melting points（ 〉 3 200 ℃）, high bending strength, high elastic modulus and high hardness.Zr B2- and Hf B2-based ceramics are promising candidates for the thermal protection components of propulsion systems,rocket nozzles,sharp leading edges and nose cones. This paper introduces the recent research progress on Zr B2- and Hf B2-based ceramics,including the synthesis methods of the boride powders,the sintering methods of the boride-based ceramics and their properties.The advantages of different synthesis methods and sintering methods are compared. The influence factors on the mechanical properties,oxidation resistance and thermal shock resistance are summarized.
文摘Urban human thermal comfort(UHTC) is affected for interacting of weather condition and underlying surface framework of urban area. Urban underlying surface temperature value and Normalized Difference Vegetation Index(NDVI) were calculated using image interpreting and supervised classification technique by ERDAS IMAGE software using 1991 and 1999 Landsat TM images data. Reference to the relational standard of assessing human thermal comfort and other meteorology data of Hangzhou City in summer, air temperature and relative humidity variation of different land types of underlying surface were inversed. By choosing discomfort index as an indictor, the spatial distribution characteristic and the spatial variation degree of UHTC were estimated and mapped on a middle scale, that is, in six districts of Hangzhou. The main characteristics of UHTC spatial variation from 1991 to 1999 were revealed using a GIS-based calculation model. The variation mechanism were analyzed and discussed from the viewpoint of city planning, construction and environmental protection.
基金Funded by the Major Research Plan of the National Natural Science Foundation of China(No.91216302)the Major State Basic Research Development Program of China(973 Program)(No.2015CB655200)the National Natural Science Foundation of China(Nos.11672088,11472092,and 11502058)
文摘ZrB_2-SiC based ultra-high temperature ceramic（UHTC） struts were firstly proposed and fabricated with the potential application in the combustor of scramjets for fuel injection and flame-holding for their machinability and excellent oxidation/ablation resistance in the extreme harsh environment. The struts were machined with electrospark wire-electrode cutting techniques to form UHTC into the desired shape, and with laser drilling to drill tiny holes providing the channels for fuel injection. The integrated thermal-structural characteristic of the struts was evaluated in high-temperature combustion environment by the propane-oxygen free jet facility, subject to the heat flux of 1.5 MW/m^2 lasting for 300 seconds, and the struts maintained integrity during and after the first experiment. The experiments were repeated for verifying the reusability of the struts. Fracture occurred during the second repeated experiment with the crack propagating through the hole. Finite element analysis（FEA） was carried out to study the thermal stress distribution in the UHTC strut. The simulation results show a high thermal stress concentration occurs at the hole which is the crack initiation position. The phenomenon is in good agreement with the experimental results. The study shows that the thermal stress concentration is a practical key issue in the applications of the reusable UHTC strut for fuel injection structure in scramjets.
基金Project supported by the National Natural Science Foundation of China(Nos.11472066 and11172336)the Chongqing Natural Science Foundation(No.cstc2013jcyj A50018)+1 种基金the Program for New Century Excellent Talents in University(No.ncet-13-0634)the Fundamental Research Funds for the Central Universities(Nos.CDJZR13240021 and CDJZR14328801)
文摘The effects of mechanical boundary conditions, often encountered in thermalstructural engineering, on the thermal shock resistance（TSR） of ultra-high temperature ceramics（UHTCs） are studied by investigating the TSR of a UHTC plate with various types of constraints under the first, second, and third type of thermal boundary conditions. The TSR of UHTCs is strongly dependent on the heat transfer modes and severity of the thermal environments. Constraining the displacement of the lower surface in the thickness direction can significantly decrease the TSR of the UHTC plate, which is subject to the thermal shock at the upper surface. In contrast, the TSR of the UHTC plate with simply supported edges or clamped edges around the lower surface is much better.
基金the National Natural Science Foundation of China(Nos.52102085 and 52072410)the National Natural Science Fund for Excellent Young Scholars(Overseas)the State Key Laboratory of Powder Metallurgy,Central South University,China(No.621022335)for financial support.
文摘Dense monolithic(Ti,Zr,Hf)C/SiC ceramic nanocomposites with four different molar ratios of metallic elements in the(Ti,Zr,Hf)C phase(i.e.,Ti:Zr:Hf=1:1:1,2:3:5,2:3:3,and 1:2:1)were prepared upon pyrolysis of novel(Ti,Zr,Hf)-containing single-source precursors(SSPs),followed by spark plasma sintering(SPS).A thorough characterization was conducted to elucidate the synthesis of the SSPs,polymer-to-ceramic transformation,chemical/phase compositions,and microstructure of the SiTiZrHfC-based ceramics.The results revealed the feasibility of synthesizing nanocomposites with high(Ti,Zr,Hf)C contents using the SSP method.These nanocomposites were characterized by a unique microstructure with in situ generated(Ti,Zr,Hf)C@C core-shell nanoparticles homogeneously mixed withβ-SiC.The ablation behavior of the nanocomposites was evaluated on an air-plasma device for 60 s.Impressively,the nanocomposites exhibited excellent ablation resistance,and the lowest linear ablation rate reached−0.58μm/s at 2200°C.Notably,the ablation resistance can be dramatically improved by precisely tailoring the atomic ratios of metal elements within the(Ti,Zr,Hf)C phase via the molecular design of the SSPs.The formation of a multiple-oxide layer with both a high-meltingpoint phase((Ti,Zr,Hf)O_(2))and low-melting-point phases((Zr,Hf)TiO_(4))and glassy SiO_(2),as well as their structure,played a critical role in the enhanced ablation resistance.The uniform distribution of the high-melting-point(Ti,Zr,Hf)O_(2)nano/microparticles throughout the glassy SiO_(2)matrix significantly enhanced the viscosity and stability of the oxide layer by the pinning effect,offering superior protection against the ingress of oxygen atoms and excellent resistance to mechanical erosion.
基金supported by the National Natural Science Foundation of China(Nos.52105233 and 52275366)the Tianjin Science and Technology Plan Project(No.22JCYBJC01590).
文摘Ultra-high temperature ceramic(UHTC)coatings are used to protect the hot-end components of hypervelocity aerocrafts from thermal ablation.This study provides a new approach to fabricate UHTC coatings with high speed laser cladding(HSLC)technology,and places more emphasis on investigating the formation mechanism,phase compositions,and mechanical properties of HSLC-UHTC coatings.Results show that a well-bonded interface between the coating and the tantalum alloy substrate can be formed.The coating is mainly composed of(Zr,Ta)C ceramic solid solution phase with a content of higher than 90% by volume and Ta(W)metal solid solution phase.At a relatively high powder feeding rate,the ZrC ceramic phase appears in the coating while a dense ZrC UHTC top layer with a thickness of up to~50μm is successfully fabricated.As for the mechanical properties of the HSLC coatings,the fracture toughness of the coating decreases with the increase of powder feeding rate.The increase of carbide solid solution phase can significantly improve the high temperature microhardness(552.7±1.8 HV0.5@1000℃).The innovative design of HSLC ZrC-based coatings on refractory alloys accomplishes continuous transitions on microstructure and properties from the substrate to the UHTC top layer,which is a very promising candidate scheme for thermal protection coating.
基金support by the European Union’s Horizon 2020 committee under research and innovation programme for the project C3 HARME:Next Generation Ceramic Composites for Harsh Combustion Environment and Space (Grant No.685594).
文摘A new additive technique for manufacturing of short fibre-reinforced ultra-refractory ceramics is presented.This technique allows the fabrication of solvent-free,thin(~100µm),flexible,and easy-to-handle sheets suitable for fabricating homogeneous or layered structures.A large range of compositions,in terms of matrix and fibre volumetric contents,from 0%to 100%is possible.The amount of short carbon fibres incorporated in the sheets ranged from 20 to 50 vol%,whereas the fibre length ranged from 3 to 5 mm.The matrix composition investigated with this technique consisted of ZrB_(2)/SiC/Y_(2)O_(3).By increasing the fibre amount from 35 to 50 vol%,an improvement of mechanical properties was observed.Four-point flexural strength(σ)ranged from 107 to 140 MPa,depending on the amount of carbon fibres(Cf).The same holds true for the work of fracture,ranging from 108 to 253 J/m^(2).Functionally graded composites were fabricated by overlapping sheets with a fibre gradient(0%-50%).
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.
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supported by the Science and Technology Innovation Program of Shanghai in 2020 (Grant No.STCSM-20520714300)the National Natural Science Foundation of China (Grant No.U19A2099)+1 种基金National Major Science and Technology Projects of China (Grant No.J2019-VIII-0003-0165)Open Project of Shanghai Key Laboratory of Spacecraft Mechanism.
文摘Spiral fibers were considered to be an ideal toughening phase of ultra-high torsional release effect.In this work,ZrB_(2)(Z)-20 vol%SiC(S)spiral fiber(ZS_(sf))with controllable structure was prepared by a combination approach of liquid rope effect and non-solvent-induced phase separation.Dominantly depended on the kinematic viscosity(η),dropping height(H),and flow rate(Q),the geometric parameters of ZS_(sf) involving filament diameter(d)and coil diameter(D)were followed the relationship of d≈0.516×10^(-3) Q^(1/2)H^(−1/4) and D≈0.25×10^(-3)(Q/H)^(1/3),respectively,within the optimizedηof 10-15 Pa·s.Three different microstructures of ZS_(sf) were achieved by adjusting the polymer/solvent/non-solvent system assisted with phase diagram calculation,including dense,hollow,and hierarchical pore structures.The ZrB_(2)-SiC with 1 wt%ZS_(sf) composites prepared by hot isostatic pressing(HIP)exhibited a~30%increase in fracture toughness(KIC,4.41 MPa·m^(1/2))compared with the ZrB_(2)-SiC composite,where the microscopic fracture toughness of the ZS_(sf) was~80%higher than that of the matrix.The fibers with a~10 nm in-situ-synthesized graphite phase amongst grain boundaries of ZrB_(2) and SiC changed the fracture mode,and promoted the crack deflection and pull-out adjacent the interface of matrix and the fiber.
基金This work received support by the EU's Horizon 2020 research and innovation programme under Grant No.685594(C^(3)HARME:Next Generation Ceramic Composites for Harsh Combustion Environment and Space)project CARBOSPACE(Ultrarefractory Ceramic Composites for Aerospace Defense Transport Energy).
文摘Ultra-high-temperature ceramic matrix composites(UHTCMCs)based on a ZrB_(2)/SiC matrix have been investigated for the fabrication of reusable nozzles for propulsion.Three de Laval nozzle prototypes,obtained by sintering with either hot pressing(HP)or spark plasma sintering(SPS),were tested 2-3 times in a hybrid rocket motor for proving reusability.Sections were extracted after oxidation tests to study the microstructural changes and oxidative and thermomechanical stresses induced by the repeated tests.Compared to a reference graphite nozzle,no measurable erosion was observed for the UHTCMC-based nozzles.The oxidation mechanism consisted in the formation of a ZrO_(2)intermediate layer,with a liquid silicon oxide(SiO_(2))layer on the surface that was displaced by the action of the gas flux towards the divergent part of the nozzle,protecting it from further oxidation.Both specimens obtained by HP and SPS displayed similar performance,with very slight differences,which were attributed to small changes in porosity.These tests demonstrated the capability of complex-shaped prototypes made of the developed UHTCMCs to survive repeated exposure to environments representative of a realistic space propulsion application,for overall operating time up to 30 s,without any failure nor measurable erosion,making a promising step towards the development of reusable rocket components.
基金supported by the National Natural Science Foundation of China(No.5207021797)the Scientific Research and Technology Development Project of China National Petroleum Corporation Limited(No.2020E-2804(JT)).
文摘Multicomponent boron-containing carbide coatings(i.e.,(Zr,Ti)C_(x)B_(y))on a C/C composite show good ablation resistance.However,the high-temperature oxidation behavior of this new type of boron-containing(Zr,Ti)C_(x)B_(y)solid solution ceramics has not been clarified yet.The present work fabricated(Zr,Ti)C_(x)B_(y)solid solution block ceramics by spark plasma sintering,and their oxidation behavior at 1600℃in air(N2–20-vol%O2)was investigated for the first time.The effects of boron on the oxidation resistance of(Zr,Ti)C_(x)B_(y)ceramics were examined.The results indicate that the(Zr,Ti)C_(x)B_(y)ceramics display good oxidation resistance with the parabolic rate law describing the oxidation process.After the trace solution of boron(0.5 wt%)into(Zr,Ti)Cx,the oxidation resistance of carbide ceramics is significantly enhanced,leading to a decrease of 30%in the oxidation rate constant.The formed oxide scale in the(Zr,Ti)C_(x)B_(y)ceramics is dense,and the interlayer shows stronger ability to inhibit inward diffusion of oxygen.In addition,the introduction of boron leads to more negative binding energy of(Zr,Ti)C_(x)B_(y)and improves the oxidation resistance of carbides.
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.
