ZrC SiC Composites Research Articles

Effect of ZrC content on the properties of biomorphic C–ZrC–SiC composites prepared using hybrid precursors of novel organometallic zirconium polymer and polycarbosilane

A novel organometallic zirconium polymer was synthesized through the copolycondensation using n-butyllithium, 1,4-diethynylbenzene, phenylacetylene and zirconium tetrachloride as raw materials. Then biomorphic C–ZrC–SiC composites were fabricated from corn stover templates by precursor infiltration and pyrolysis process using hybrid polymeric precursors containing the organometallic zirconium polymer and polycarbosilane. The microstructure, mechanical properties and oxidation resistance of the composites were investigated. With ZrC content increasing, the mechanical properties of the composites were enhanced due to dispersion strengthening and grain fining of the homogeneously dispersed ZrC nanoparticles. The oxidation behavior of C–SiC–ZrC indicated that the oxidation resistance of the composite was reduced at 1000 °C but improved at 1500 °C with the increase of ZrC content. The improved oxidation resistance was mainly attributed to a proper ZrC content, the formation of ZrSiO4 layer on the surface of the composite, and its matrix microstructure characterized by a nano-sized dispersion of ZrC–SiC phases.

Thermal ablation behavior of SiC coating for 3D braided carbon fiber reinforced ZrC-SiC composites in different heat fluxes

In this study, CVD-SiC coating was prepared on 3D braided carbon fiber reinforced ZrC-SiC (abbreviated as Cf/ZrC-SiC) composites, and the microstructure and morphology of the composites and coating were characterized by scanning electron microscopy coupled with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD). The effect and mechanism of CVD-SiC coating on the ablation properties of Cf/ZrC-SiC composites under different ablation conditions were studied in details. The results showed that the CVD-SiC coating could reduce the ablation temperature and improve the compactness, which will promote the ablation properties of the Cf/ZrC-SiC composites in the heat flux of 2.38 MW/m2. But with the heat flux increasing to 4.18 MW/m2, ablation properties of Cf/ZrC-SiC composites decreased significantly, it was mainly difficult to form dense and stable ZrO2-SiO2 protective oxides due to accelerated mechanical erosion which makes the CVD-SiC coating lose its protection for Cf/ZrC-SiC composites during ablation and higher ablation temperature which will aggravate active oxidation of SiC and the evaporation of SiO2.

A thermoset hybrid sol for the syntheses of zirconium carbide–silicon carbide foam via replica method

Zirconium carbide–silicon carbide (ZrC–SiC) ceramics are amongst the promising candidate materials for thermal protection structures in hypersonic re-entry space vehicles. A thermoset hybrid sol for the syntheses of monolithic ZrC–SiC composites was prepared by a simple sol–gel method. Furfuryl alcohol, polyzirconoxane and tetraethyl orthosilicate were used as raw materials. The as-synthesized sol can be cured at 85 °C for 24 h to obtain a bulk gel. The cured gel is converted into porous ZrC–SiC monolith with porosity of 44.1% after pyrolysis at 1500 °C for 1 h in vacuum. The ZrC–SiC monolith is composed of well distributed nano-sized ZrC and SiC particles. Highly porous ZrC–SiC ceramic foam with density of 0.34 g/cm3 and porosity of 78.1% is prepared by replica method using the hybrid sol as precursor and melamine foam as templates. The hybrid sol and ZrC–SiC composites are characterized by FT-IR, TG–DTA, XRD, SEM, EDS and TEM.

In situ synthesis, microstructure and mechanical properties of nano-structured SiC-ZrC composite prepared by spark plasma sintering

The synthesis route, microstructure and mechanical properties of SiC-ZrC composites prepared from a mixture of ZrSi2-C powders by reactive spark plasma sintering (R-SPS) were investigated. The reaction between ZrSi2 and C began to occur at 550 °C and mostly completed at 1300 °C. On the other hand, the densification during SPS occurred mainly between 1490 °C and 1750 °C, indicating that the reaction did not directly promote the densification. A fully dense SiC-ZrC composite (relative density > 99%), in which fine SiC (∼260 nm) and ZrC (∼360 nm) grains distributed homogeneously, was prepared by SPS at 1750 °C under a pressure of 40 MPa. The formation of nano-composites can be ascribed to the high energy ball milling of raw materials, fine ZrC and SiC grains formed during R-SPS, and low sintering temperature by R-SPS process. The Vickers hardness, fracture toughness and Young's modulus of the composite were 23.3 GPa, 2.87 MPam1/2, and 319 GPa, respectively.

SiCnw/PyC core-shell networks to improve the bonding strength and oxyacetylene ablation resistance of ZrB2–ZrC coating for C/C–ZrB2–ZrC–SiC composites

To enhance the bonding strength and oxyacetylene ablation resistance of the ZrB2–ZrC coated C/C–ZrB2–ZrC–SiC composites obtained by the combination of supersonic atmosphere plasma spray (SAPS) and precursor infiltration and pyrolysis (PIP), novel SiC nanowire (SiCnw)/pyrolytic carbon (PyC) core-shell structures are designed and introduced into the coating. Compared to SiC nanowires which are widely added into ceramics, metals and so on, SiCnw/PyC core-shell structures have a better cohesion. Additionally, the bonding strength of coating can be largely improved through the toughening mechanism of SiCnw/PyC structures. After being exposed to oxyacetylene ablation torch, the best ZrB2–ZrC coated C/C–ZrB2–ZrC–SiC specimens with SiCnw/PyC networks possess a linear ablation rate of −0.9 ± 0.5 μm/s and a mass ablation rate of −0.3 ± 0.6 mg/s, while the linear and mass ablation rates of the C/C–ZrB2–ZrC–SiC specimens for comparison are up to 4.2 ± 1.0 μm/s and 1.2 ± 0.8 mg/s, respectively. The significant improvement of oxyacetylene ablation resistance is attributed to a lower surface temperature during ablation, a lower thermal stress in the coating, and a better bonding strength of the coating/substrate interface owing to the introduction of SiCnw/PyC core-shell structures.

Effect of ZrC–SiC content on microstructure and ablation properties of C/C composites

C/C–ZrC–SiC composites with different ZrC–SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C–SiC and C/C–ZrC–SiC composites exhibited good ablation resistance under the plasma flame above 2300 °C. With the increase of ZrC content, a continuous oxide layer and a solid Zr–Si–O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC–SiC ceramics. The solid ZrO2–ZrC and Zr–Si–O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2–ZrO2–ZrC–SiC layer would serve as a thermal and oxygen barrier for preventing the substrate from further ablation. The C/C–ZrC–SiC composites with 27.2% ZrC and 7.56% SiC shows superior ablation resistance, and the mass and linear ablation rates are −3.51 mg/s and −1.88 μm/s, respectively.

Mechanical Property, Oxidation and Ablation Resistance of C/C–ZrB2–ZrC–SiC Composite Fabricated by Polymer Infiltration and Pyrolysis with Preform of Cf/ZrB2

C/C–ZrB2–ZrC–SiC composites were fabricated by polymer infiltration and pyrolysis (PIP) with a preform of Cf/ZrB2. The carbon fibers and the resin carbon were coated with ceramic layer after PIP in the composites. The composite presents a pseudo-plastic fracture due to deflection of cracks and pullout of fibers. The composite has a higher bending strength by this method in comparison with the conventional PIP process due to fewer heat treatment cycles. The static oxidation test shows that the mass loss of the composites is no more than 1% after 20 min oxidation at 1100 °C. The “core–shell” structure between ZrC–SiC ceramic and other phases plays a positive role in preventing the inward diffusion of oxygen. The ablation resistance of the C/C–ZrB2–ZrC–SiC composite samples was tested using a plasma generator. After ablation for 120 s, the mass and linear ablation rates of the composites are 4.65 mg cm−2 s−1 and 2.46 µm s−1, respectively. The short carbon layer shows a better ablation resistance than the nonwoven carbon fabric layer after the ceramic coating is peeled off because of its higher ceramic content.

Reactive hot pressing of SiC-ZrC composites at low temperature

SiC-ZrC composites with relative density in excess of 99% were prepared by reactive hot pressing (RHP) of SiC and ZrH2 at 1800°C for 1h. The reaction between SiC and ZrH2 resulted in the formation of ZrC1-x. The formation process and densification behavior during RHP process were investigated. Low temperature densification of SiC-ZrC composites is attributed to the formed nonstoichiometric ZrC1-x and the removal of SiO2 impurity on the surface of SiC particles. As reinforced phase, ZrC1-x has inhibiting effect on the abnormal grain growth of SiC, resulting in homogeneous microstructure of fine SiC grains. Adding 10wt% ZrH2 to SiC, the formed SiC-4.62vol% ZrC composite exhibited better mechanical properties (Vickers hardness of 27.6±0.7GPa, flexure strength of 448±38MPa, fracture toughness of 6.0± 0.3MPa·m1/2, respectively) than monolithic SiC ceramic.

Microwave-assisted Synthesis of a ZrC-SiC Nanocomposite by Carbothermal Reduction and its Effect on Mean Particle Size

ZrC-SiC nanopowders were prepared by carbothermal reduction of ZrO2 and SiO2 with carbon black in argon gas atmosphere, using microwave energy as an alternative heating source. The samples were characterized by XRD, SEM and BET surface area analysis. The results indicate that highly crystalline ZrC-SiC composites with a mean particle size of about 80 nm can be synthesized at a relatively low temperature (~1420 °C). Microwave-assisted heating to obtain the ZrC-SiC nanopowders significantly reduces the synthesis time to only 40 min when compared with the long reaction times involved in conventional carbothermal reduction, which requires about 8 hours to obtain ZrC and 2 hours to obtain SiC.

Fabrication and microstructure of 3D Cf /ZrC-SiC composites: through RMI method with ZrO2 powders as pore-making agent

3D Cf/ZrC–SiC composites were prepared by a combination process of slurry infiltration and reactive melt infiltration. ZrO2 powders and ZrSi2 alloy, both of which reacted with amorphous carbon, were used as pore-making agent and infiltrator, respectively. After carbothermal reduction at 1650°C, X-ray diffraction analysis revealed that ZrO2 powders were completely converted into ZrC by reacting with amorphous carbon, and an in-situ formed submicron porous configuration was observed at the areas containing ZrO2. Results showed that the matrix in composites mainly consisted of SiC, ZrC and a small quantity of residual metal. SEM and TEM images revealed the formation of ZrC or SiC intergranular particles in the matrix and the characteristic around the residual resin carbon. The composites had a bending strength of 94.89±16.7MPa, fracture toughness of 11.0±0.98MPam1/2, bulk density of 3.36±0.01g/cm3, and open porosity of 4.64±0.40%. The formation mechanisms of ZrC–SiC dual matrix and intrabundles׳ structure were discussed in the article.

Effects of high-temperature annealing on the microstructures and mechanical properties of C/C–ZrC–SiC composites prepared by precursor infiltration and pyrolysis

C/C–ZrC–SiC composites were fabricated by precursor infiltration and pyrolysis (PIP) process. A mixture solution of organic zirconium-containing polymer and polycarbosilane was chosen as the precursor. The porous carbon/carbon (C/C) preforms were first infiltrated in the precursor under vacuum, dried under 80°C and then pyrolyzed at 1500°C. After 20cycles of PIP process, C/C–ZrC–SiC composites were obtained. The composites were further treated at 1650°C and 1800°C at an argon atmosphere for 2h, respectively. The effects of high-temperature annealing on the microstructures and mechanical properties of C/C–ZrC–SiC composites were investigated. Results show that the density decreases and the different ceramic phases of the matrix get separated gradually as the annealing temperature increases. The mechanical strength decreases slightly after annealed at 1650°C, and the downward trend is more obvious under 1800°C in comparison to the unannealed composites. The fracture behavior of the composites changes after heat treatment. The decline of the strength and the change of the mechanical behaviors are attributed to the microstructural changes which include pores, cracks, fiber damage, weak interfacial bonding and ceramic phase separation caused by the annealing.

Ablation behaviour of C/C and C/C–ZrC–SiC composites with cone-shaped holes under an oxyacetylene flame

The ablation behaviour of C/C and C/C–ZrC–SiC composites with cone-shaped holes was studied under an oxyacetylene flame in two heat fluxes. The results showed that C/C–ZrC–SiC composites had a superior ablation resistance in the heat flux of 2.38MW/m2, mainly owing to the ZrO2–SiO2 with double structure formed on the surface. As ablated in the heat flux of 4.18MW/m2, the ablation resistance of C/C–ZrC–SiC composites was worse than that of C/C composites since the high temperature corrosion resulted in a heavy evaporation of SiO2 and the left ZrO2 skeleton was easily scoured away by the strong scouring force of flame.

Fabrication and crack propagation behaviour of laminated ZrC–SiC composites

Laminated ZrC–SiC composites were fabricated by a tape-casting process and vacuum hot-pressing. The microstructures, fracture behaviour, and crack propagation paths of the resulting composites were studied. The laminated ZrC–SiC composite had a bending strength of 167MPa and exhibited non-brittle failure behaviour due to the propagation and deflection of cracks. The observed crack propagation path in the ZrC–SiC laminated composites indicated that crack deflection and crack termination were observed during the fracture process. The crack tip decreased as the crack traversed through each layer.

Microstructures and mechanical properties of laminated ZrC–SiC composites with different SiC powders

Laminated ZrC–SiC composites with different SiC powders were prepared through tape casting and hot pressing. Two different SiC powders, with sizes of 10μm and 800nm, were introduced into the laminated ZrC–SiC composite. The results show that there are obvious crack deflection and prolonged crack length in the laminated structure. Moreover, the composite B with a mean SiC particle size of 800nm is more compact than composite A (with mean SiC particle size of 10μm). The Si elements in composite A and composite B are pressed into the ZrC layer; fewer Zr elements spread to the SiC layer. The diffusion of Si elements of the SiC(2) (SiC particle size of 800nm) layer is easier and more uniform. Moreover, composite B has a higher density, lower porosity, and higher flexural strength than composite A.

Carbon nanotube-toughened interlocking buffer layer to improve the adhesion strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites

Abstract For the purpose of improving the interface adhesion strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, a carbon nanotube (CNT)-toughened interlocking buffer layer was constructed between the SiC coating and C/C–ZrC–SiC substrates by pre-oxidation and chemical vapor deposition. After incorporating CNTs, the fracture toughness of the buffer layer increased by 55.7%. The interface adhesion strength between SiC coating and C/C–ZrC–SiC composites was up to 6.8 N, which was 195.7% higher than that of the SiC coated specimens without CNT-toughened interlocking buffer layer. After 25-time thermal shock cycling between 1773 K and room temperature, the mass loss of the coated specimens decreased by 64.4%. The significant enhancement of interface bonding strength and thermal shock resistance of SiC coating was mainly due to the simultaneous existence of micron scale “pinning effect” of the inlaid SiC coating and nanoscale toughing mechanism of CNTs.

Corrosion behavior of ZrC–SiC composite ceramics in LiF–NaF–KF molten salt at high temperatures

The suitability of ZrC–SiC-based ceramics was assessed as candidate materials for fluoride. An immersion corrosion with ZrC–SiC composites was performed in molten FLiNaK salts (LiF–NaF–KF: 46.5/11.5/42mol%) at 850°C. Results indicated that ZrC–SiC-based ceramics were more corrosion resistant than the ZrC ceramic. ZrC–40SiC ceramic exhibited 50% weight-loss to ZrC. This carbide exhibited minimal corrosion attack because of strong resistance to dissolution in molten fluorides. Furthermore, XRD results were consistent with weight-loss and SEM results. The corrosion behavior of ZrC–SiC-based ceramics was affected by impurities, particularly oxygen content. Oxygen and/or oxygen ion participated in corrosion of ceramic. Corrosion of carbide ceramics is mainly due to C4− in ceramics. This ion is oxidized to elemental C by oxidants or impurities in the molten salt. The addition of C may inhibit corrosion of molten salts and thus improve the corrosion resistance of carbide ceramics.

Ablation mechanism of C/C–ZrB2–ZrC–SiC composite fabricated by polymer infiltration and pyrolysis with preform of Cf/ZrB2

C/C–ZrB2–ZrC–SiC composites were fabricated by polymer infiltration and pyrolysis (PIP) with a preform of Cf/ZrB2. The ZrB2 powders were sprayed onto fabric layer by layer before the fabric is needled. After introduction of resin carbon and ZrC–SiC into the preform, a ceramic coating on the matrix and fibres was formed in the composites. The plasma ablation test indicates that the composites possess a good ablation resistance after ablation for 180s and 240s. The SiO2–ZrO2 barrier layer, high temperature Zr–Si–O glass layer and heat dissipation all contribute to the good ablation resistance of the composites.

Effect of carbon nanotubes on the toughness, bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites

In order to improve the toughness, interface bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, carbon nanotubes (CNTs) were prepared by injection chemical vapor deposition and attempted as the reinforcement materials in the SiC coating. After incorporating CNTs, the hardness and elastic modulus of the SiC coating increased by 26.37% and 28.23%, respectively. The interface bonding strength between SiC coating and C/C–ZrC–SiC composites was enhanced by 53.31%. The mass loss of the SiC coated C/C–ZrC–SiC composites after thermal shock between 1773K and room temperature for 15 times decreased from 5.98% to 1.98%. The incorporation of CNTs can effectively improve the toughness, interface bonding strength and thermal shock resistance of SiC coating due to the nanoscale toughening mechanism of CNTs by pullout, bridging and crack deflection.

Effect of pre-oxidation treatment on the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites

To improve the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, a transition layer with mechanical interlocking structure was constructed at the interface by pre-oxidation treatment and chemical vapor deposition. For the coated specimens with pre-oxidation treatment at 1073K for 5min, the bonding strength increased from 2.0 to 4.0N, and the mass loss percentage decreased by 52.5% after 12-time thermal cycling between 1773K and room temperature in air. The transition interlocking structure can effectively alleviate the mismatch between the coefficients of thermal expansion of SiC coating and C/C–ZrC–SiC substrate, improving the bonding strength and thermal shock resistance. As the pre-oxidation time increases, a rugged and loose ZrO2–SiO2 layer will be formed at the interface, which is disadvantageous to the bonding strength and thermal shock resistance of SiC coating for C/C–ZrC–SiC composites, and results in the debonding and collapse of the coating.

Elaboration of ZrC-SiC composites by spark plasma sintering using polymer-derived ceramics

The combination of Polymer-Derived Ceramics (PDC) and Spark Plasma Sintering (SPS) was used in order to synthesize ZrC-SiC composites containing 10 to 40wt.% SiC. The whole process was studied: cross-linking of the SiC pre-ceramic polymer, mixing with commercial ZrC powders followed by pyrolysis and ball milling steps, and finally densification of the composite material using SPS. The optimized SPS conditions consist in the choice of an applied load of 50MPa under vacuum, and a soaking temperature of 2223K for 15min. High relative densities were reached under these conditions (94 to 100%). Furthermore, the addition of SiC gave an increase in the elastic moduli and hardness, which reached a maximum at 20wt.% SiC.