Ultra-high Temperature Ceramic Composites Research Articles

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

AbstractRoom and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB2 ultra‐high temperature ceramic (UHTC) particulate filled Cf/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc‐jet testing of the UHTC composites highlighted the excellent ultra‐high temperature oxidation performance of these materials.

Effect of carbon nanotube on processing, microstructural, mechanical and ablation behavior of ZrB2-20SiC based ultra-high temperature ceramic composites

Herein, zirconium diboride (ZrB2) is reinforced with silicon carbide (SiC) and carbon nanotube (CNT) to provide enhanced structural stability and oxidation protection against extreme thermal (>2400 °C) and oxidative environments. The ablation resistance of ZrB2-based composites was evaluated using plasma arc-jet with a heat-flux of 2.5 MW/m2 for 30 s, and the decreased oxidation-rate (from 0.77 μm/s to 0.44 μm/s) is attributed to enhanced thermal conductivity (42.3–52.3 W/mK at 1200 °C) with synergistic reinforcement of SiC and CNT. The increased onset temperature (from 679 °C to 706 °C) and decreased enthalpy of oxide formation (from 1.6 to 0.6 kJ/g), insinuates an increase in thermal stability and oxidation resistance with the synergistic addition of both SiC and CNT in ZrB2. The increase in the hardness of ZrB2 in the as-processed composites (up to 1.6 times) as well as after plasma arc jet exposure (up to 2.1 times) with synergistic reinforcement of SiC and CNT has shown to suppress crack-formation and restrict oxidation. The reduction in the analytically evaluated tensile interfacial residual stress indicates enhanced structural integrity of ZrB2-SiC-CNT composites, which is a mandatory requirement for aerospace applications.

Effect of SiC content on electrical, thermal and ablative properties of pressureless sintered ZrB2-based ultrahigh temperature ceramic composites

The effects of SiC content (10–40 vol.%) on electrical, thermal and ablation properties of pressureless sintered ZrB2-SiC composites showing interfacial segregation of W-rich phases have been studied. The electrical resistivity was measured by four-probe method, whereas thermal diffusivity and coefficient of thermal expansion (CTE) were determined using laser-flash method and thermo-mechanical analyzer, respectively. Whereas thermal conductivities calculated from experimentally obtained thermal diffusivity values are found to be the highest for the ZrB2-20 SiC composite, both electrical conductivity and CTE decrease with increasing SiC content. The specimens were subjected to thermal shock by soaking at 800–1200°C, followed by water-quenching. Further, some specimens were exposed to oxyacetylene flame (2200°C) for 10min. The damage was estimated from changes in mass, Young’s modulus, and hardness. The highest thermal shock and ablation resistance have been observed for the ZrB2-20 SiC composite, as thermal properties and formation of protective oxide scale play key role.

Design, Preparation and Properties of Carbon Fiber Reinforced Ultra-High Temperature Ceramic Composites for Aerospace Applications: A Review

Carbon fiber reinforced ultra-high temperature ceramic (UHTC) composites, consisting of carbon fibers embedded in a UHTC-matrix or a C–SiC–UHTC-matrix, are deemed as the most viable class of materials that can overcome the poor fracture toughness and thermal shock resistance of monolithic UHTC materials, and also improve the oxidation resistance and ablation resistance of C/C and C/SiC composites at ultra-high temperatures. In this review, we summarize the different processing routes of the composites based on the UHTC introducing methods, including chemical vapor infiltration/deposition (CVI/D), precursor infiltration and pyrolysis (PIP), reactive melt infiltration (RMI), slurry infiltration (SI), in-situ reaction, hot pressing (HP), etc; and the advantages and drawbacks of each method are briefly discussed. The carbon fiber reinforced UHTC composites can be highly tailorable materials in terms of fiber, interface, and matrix. From the perspective of service environmental applications for engine propulsions and hypersonic vehicles, the material designs (mainly focusing on the composition, quantity, structure of matrix, as well as the architecture of carbon fibers, UHTCs and pores), their relevant processing routes and properties (emphasizing on the mechanical and ablation properties) are discussed in this paper. In addition, we propose a material architecture to realize the multi-function through changing the distribution of carbon fibers, UHTCs and pores, which will be an important issue for future development of carbon fiber reinforced UHTC composites.

Fabrication of ultra high temperature ceramic matrix composites using a reactive melt infiltration process

Fiber reinforced composites containing a ZrB2 matrix are prepared by reactive melt infiltration, using a Zr based intermetallic compound. The reactive melt infiltration process is further characterized by determining the contact angle of the different melt and preform elements. Two different methods for boron powder impregnation of the preforms, which form ZrB2 during Zr2Cu melt infiltration, are evaluated. Degradation of fibers and different fiber coatings for Zr2Cu melt are evaluated and the microstructure of the infiltrated samples is investigated by means of XRD and SEM.

Oxidation studies on TaC based ultra-high temperature ceramic composites under plasma arc jet exposure

An ultra-high temperature ceramic, TaC, is reinforced with SiC and carbon nanotubes (CNTs) to provide protection under extreme thermal and chemical environments. High temperature performance of spark plasma sintered TaC-based composites was evaluated through plasma arc-jet exposure under heat-flux of 2.5MW/m2 for 30s. The composite shows a significant improvement in the oxidation resistance compared to that of TaC. Complimentarily, thermogravimetric analyses (up to 1500°C) elicits shift in the onset temperature of oxide formation from 735°C in TaC to 901°C (with synergistic addition of both SiC and CNT) insinuating the enhanced thermal stability of TaC-SiC-CNT composites.

Heat flux mapping of oxyacetylene flames and their use to characterise Cf-HfB2 composites

Cost effective and fast ultra-high-temperature testing methods such as oxyacetylene torch testing are extremely useful for the rapid screening of ultra-high-temperature ceramic (UHTC) materials for hypersonic applications. There is no report in the literature, however, of an organised study to measure the heat flux and how it varies with gas flow rate, gas flow ratio and distance from the nozzle tip for an oxyacetylene flame. In this paper, the authors report for the first time the heat flux mapping of an oxidising, neutral and reducing flame. The measured heat flux was as high as ∼17 MW m−2 at a distance of 10 mm from the nozzle, which is much higher than that previously reported in the literature. Torch testing was carried out for Cf-HfB2 UHTC composites at this heat flux and the results are presented along with detailed microstructural characterisation.

Additive Manufacturing of Reactive In Situ Zr Based Ultra-High Temperature Ceramic Composites

Reactive in situ multi-material additive manufacturing of ZrB2-based ultra-high-temperature ceramics in a Zr metal matrix was demonstrated using LENS™. Sound metallurgical bonding was achieved between the Zr metal and Zr-BN composites with Ti6Al4V substrate. Though the feedstock Zr power had α phase, LENS™ processing of the Zr powder and Zr-BN premix powder mixture led to the formation of some β phase of Zr. Microstructure of the Zr-BN composite showed primary grains of zirconium diboride phase in zirconium metal matrix. The presence of ZrB2 ceramic phase was confirmed by X-ray diffraction (XRD) analysis. Hardness of pure Zr was measured as 280 ± 12 HV and, by increasing the BN content in the feedstock, the hardness was found to increase. In Zr-5%BN composite, the hardness was 421 ± 10 HV and the same for Zr-10%BN composite was 562 ± 10 HV. It is envisioned that such multi-materials additive manufacturing will enable products in the future that cannot be manufactured using traditional approaches particularly in the areas of high-temperature metal–ceramic composites with compositional and functional gradation.

Aqueous Electrophoretic Deposition of ZrB2-SiC Nano-composites in Pulsed DC Electric Fields

ZrB2-SiC ultra-high temperature ceramic composites have been considered to be the optimal candidate for using in extreme environments. The present communication for the first time applied aqueous electrophoretic deposition for successfully preparing ZrB2-SiC nano-composites in pulsed DC electric fields. The deposition behavior was investigated based on the influences of applied voltage, duty cycle and frequency. A smooth, uniform and pore-free ZrB2-SiC nano-composite was successfully synthesized. The highest green density of 67.1% was achieved for the nano-composite with the SiC content of 26.7 wt.%. We believe that the present research will open up a new horizon in preparing bulk ceramic composites or composite working parts in industries.

Metallocene Catalytic Insertion Polymerization of 1-Silene to Polycarbosilanes.

Metallocene of zirconium were used as a catalyst for an insertion polymerization of 1-methylsilene directly into pre-ceramic precursor polyzirconocenecarbosilane (PZCS) during dechlorination of dichlorodimethylesilane by sodium, which exhibits high catalytic effectiveness with the maximum conversion ratio of polycarbosilane up to 91%. The average molecular weights of polymers synthesized are less than 1400, all with very narrow polymolecularities. The mechanism of catalytic polymerization was assumed to be similar to a coordination insertion polymerization of 1-olefins by metallocenes. The obtained PZCS show high ceramic yields with formation of composite ceramics of ZrC-SiC, which are novel polymeric precursors of ultra-high temperature ceramic (UHTC) fiber and composite.

Temperature dependence of elastic properties of ZrB2–SiC composites

Elastic properties (Young׳s modulus, shear modulus, and Poisson׳s ratio) of ZrB2, SiC ceramics and ZrB2–SiC ultra high temperature ceramic composites were measured by the Impulse Excitation technique in the RT–1173K temperature range. Two compositions of ZrB2 with 17vol% and 32vol% of SiC strengthening phase were hot pressed to almost full density, followed by machining before the measurements took place. The temperature dependences of elastic properties have shown the expected softening behavior, where only small 4% and 5% linear reduction in Young׳s and shear moduli were detected, respectively, for ZrB2–17vol% SiC and ZrB2–32vol% SiC ceramic composites. The reported decrease in elastic moduli brings the respective linear increase of Poisson׳s ratio up to ~9% in the temperature of interest. Such high temperature behavior corresponds well to the upper and lower bounds of elastic moduli of two ZrB2–SiC ceramic composites calculated by Voigt and Reuss estimations using properties of pure ZrB2 and pure SiC ceramics, as published in the literature.

Gas tungsten arc welding of ZrB2–SiC based ultra high temperature ceramic composites

Abstract The difficulty in fabricating the large size or complex shape limits the application of ZrB 2 –SiC composites. Joining them by fusion welding without or with preheating, controlled cooling under protective gas shield leads to thermal shock failure or porosity at the weld interface. In the present work, a filler material of (ZrB 2 –SiC–B 4 C–YAG) composite with oxidation resistance and thermal shock resistance was produced in the form of welding wire. Using the filler, gas tungsten arc welding (GTAW) was performed without employing preheating, post controlled cooling and extraneous protective gas shield to join hot pressed ZrB 2 –SiC (ZS), and pressureless sintered ZrB 2 –SiC–B 4 C–YAG (ZSBY) composites to themselves. The fusion welding resulted in cracking and non-uniform joining without any filler material. The weld interfaces of the composites were very clean and coherent. The Vickers micro-hardness across the weld interface was found to increase due to the increase in the volume % of both SiC and B 4 C in the filler material. The shear strength of the weld was about 50% of the flextural strength of the parent composite.

Significance of hot pressing parameters and reinforcement size on sinterability and mechanical properties of ZrB2–25 vol% SiC UHTCs

The influences of hot pressing parameters and SiC particle size on the bulk density, the average ZrB2 grain size and Vickers hardness of ZrB2–25vol% SiC ultrahigh temperature ceramic composites were investigated. In this paper, the Taguchi methodology (An L9 orthogonal array) was used to specify the contributions of four parameters: the hot pressing temperature, holding time, applied pressure and SiC particle size. The experimental procedure included nine tests for four parameters with three levels which were employed to optimize the process parameters. The statistical analyses recognized the hot pressing pressure and temperature as the most consequential parameters affecting the density and hardness of ZrB2–SiC composites. The SiC particle size and holding time were specified as the most effective parameters on the average ZrB2 grain size. The bulk density, average ZrB2 grain size, Vickers hardness and fracture toughness of the sample, hot pressed at optimal conditions (1850°C, 90min, 16MPa and 200nm), reached about 5.36g/cm3, 10.03µm, ~17.1GPa and 5.9MPam1/2, respectively. The confirmation test, carried out under optimum conditions, showed that the experimental results were relatively equal to the predicted values from the Taguchi prediction model. Finally, the mechanisms of enhanced fracture toughness of the hot pressed ZrB2–SiC ceramic composites were discussed.

Research progress on ultra-high temperature ceramic composites

Ultra-high temperature ceramics (UHTCs) are composed of ZrC, ZrB2, HfC, HfB2, HfN and TaC and their melting points are higher than 3000℃. They are a vital class of high temperature structural materials and have attracted a great deal of attention in the past two decades in fundamental research and in technological applications. The ZrB2-SiC and HfB2-SiC UHTC composites, in particular, have excellent oxidation/ablation resistance, moderate thermal shock resistance and high strength retention at elevated temperature. They can survive oxidizing environments at temperatures of 2000℃ and higher. These properties make them the most promising materials for use in extreme environments such as hypersonic flight, atmospheric re-entry, and rocket propulsion. ZrB2-based and HfB2-based UHTCs have similar oxidation and ablation behaviors however as ZrB2-based UHTCs are lighter and less expensive, they are used as aerospace materials. Here we provide a comprehensive review of UHTC composites including their preparation, mechanical properties, thermal shock resistance, oxidation/ablation properties and thermal response, with a particular focus on ZrB2-based UHTCs. UHTCs were generally fabricated by hot pressing, spark plasma sintering, pressureless sintering, reactive hot pressing and sinter forging. Hot pressing is the dominant densification technique for the preparation of UHTCs. The flexural strength of UHTCs decreases with an increase in grain size and it exhibits a strong correlation with the size of the SiC particulates. However, the fracture toughness trend is not consistent with that of strength and therefore the matching of grain size becomes important. UHTCs display plasticity at elevated temperature and their brittle-to-ductile transition temperature (1500℃) strongly depends on the grain size and the purity of the grain boundaries. Catastrophic failure occurs easily during the heating or cooling process. The thermal shock resistance of UHTCs is a major issue for future applications. The methods used to improve the thermal shock resistance of UHTCs are summarized from critical thermal shock temperature and strength retention rate after thermal shock testing points of view. The oxidation behavior of UHTCs significantly depends on the temperature and the temperature limits of the applications of these materials are analyzed. The effect of the additives on the overall performance of the resultant composites as well as the relationship between material composition, microstructure and performance are also discussed in detail. This provides useful insights into effective design principles to optimize the overall structural performance of ultra-high temperature ceramic composites according to special service environments. The remaining challenges and future outlook of this field are also addressed.

High temperature fracture behavior of ZrB2–SiC–graphite composite in vacuum and air

Hot pressed ZrB2–SiC–graphite ultra high temperature ceramic composites were prepared for the fracture toughness tests in vacuum up to 1800°C and in air up to 1300°C. Measured results show that a brittle–ductile transition temperature of ZrB2–SiC–graphite composite is deduced to be 1300°C, and ZrB2–SiC–graphite composite exhibits a linear behavior below 1300°C. Fracture toughness in vacuum linearly decreases with the increase of temperature below 1300°C, increases from 1300°C to 1600°C, and has a rapid reduction at 1800°C. The phenomenon can be attributed to the relaxation of thermal residual stress under 1300°C, the existence of plastic flow from 1300°C to 1600°C, and the degeneration of graphite flakes and cavitation formation at 1800°C. In comparison to vacuum, the fracture toughness in air improves by the healing effect of pre-oxidation below 1300°C. The microstructure observations further reveal the great effects of temperature and pre-oxidation on the fracture behavior of ZrB2–SiC–graphite composite.

SPS densification and microstructure of ZrB2 composites derived from sol–gel ZrC coating

A technique for densifying ultra high temperature ceramic composites while minimising grain growth is reported. As-purchased ZrB2 powder was treated with a zirconia-carbon sol–gel coating. Carbothermal reduction at 1450 ◦ C produced 100–200 nm crystalline ZrC particles attached on the surface of ZrB2 powders. The densification behaviour of the sol–gel coated powder was compared with both the as-purchased ZrB2 and a compositionally similar ZrB2–ZrC mixture. All three samples were densified by spark plasma sintering (SPS). The ZrB2 reference sample was slow to densify until 1800 ◦ C and was not fully dense even at 2000 ◦ C, while the sol–gel modified ZrB2 powder completed densification by 1800 ◦ C. The process was studied by ram displacement data, gas evolution, SEM, and XRD. The sol–gel coated nanoparticles on the ZrB2 powder played a number of important roles in sintering, facilitating superior densification by carbothermal reduction, nanoparticle coalescence and solid-state diffusion, and controlling grain growth and pore removal by Zener pinning. The sol–gel surface modification is a promising technique to develop ultra-high temperature ceramic composites with high density and minimum grain growth. © 2014 Elsevier Ltd. All rights reserved.

Characterization of Structure-Thermo-Mechanical Properties of Ultra High Temperature Ceramic Composites (UHTCCS) By Nondestructive Testing (NDT)

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Flexural creep of zirconium diboride–silicon carbide up to 2200°C in minutes with non-contact electromagnetic testing

Abstract Flexural creep of ZrB 2 –30 vol% SiC ultra high temperature ceramic composite was studied at 1700–2200 °C and 20–50 MPa using the novel method of electromagnetic Lorentz force loading of electrically heated specimens. Experiments were conducted in air and in non-oxidizing atmospheres. The apparent activation energy for creep was 344 ± 35 kJ/mol for non-oxidizing conditions. The stress exponent was 1.4 ± 0.4. The creep rate was slightly higher in air due to a decrease in the size of the load bearing substrate because of oxidation. There was no evidence of electric field effects. Creep experiments could be performed up to 2200 °C very quickly, with experiments conducted in a few minutes.

Effect of SiC Content on the Ablation and Oxidation Behavior of ZrB₂-Based Ultra High Temperature Ceramic Composites.

The ablation and oxidation of ZrB2-based ultra high temperature ceramic (UHTC) composites containing 10%, 15% and 30% v/v SiC were tested under different heat fluxes in a high frequency plasma wind tunnel. Performance was significantly affected by the surface temperature, which was strongly dependent on the composition. Composites containing 10% SiC showed the highest surface temperature (>2300 °C) and underwent a marked degradation under both conditions. In contrast, composites with 30% SiC exhibited the lowest surface temperature (<2000 °C) and demonstrated excellent ablation resistance. The surface temperature of UHTCs in aerothermal testing was closely associated with the dynamic evolution of the surface and bulk oxide properties, especially for the change in chemical composition on the exposed surface, which was strongly dependent on the material composition and testing parameters (i.e., heat flux, enthalpy, pressure and test time), and in turn affected its oxidation performance.

Modification of ZrB2 powders by a sol–gel ZrC precursor—A new approach for ultra high temperature ceramic composites

A simple method of integrating a powder processing technique with a sol–gel process to produce ultra high temperature ceramic (UHTC) composites is reported. ZrB2 powder was treated with a zirconium oxide-carbon sol–gel coating. Carbothermal reduction produced nanosized crystalline ZrC grains on the surface of ZrB2 powder. Detailed refinement of carbon content in the sol–gel coating was necessary to control the oxide reduction on the ZrB2 surface, while providing intrinsic carbon for the nanoparticle sol–gel phase. Microstructures and crystalline phases were analyzed using TEM, SEM, and XRD. It was found that carbothermal reduction of ZrO2 to form nano ZrC can be completed on the surface of ZrB2 at 1450 °C. The sol–gel coating creates a homogenous mix of ~200 nm ZrC in close proximity to the ZrB2 surface. Densification of the ZrB2-ZrC composite can be achieved by spark plasma sintering at 1800 °C. The amount of carbon added to the sol–gel precursor needs to be carefully tailored to dictate the final porosity and grain size of sintered composites.