Ablation resistance of HfC(Si,O)-HfB2(Si,O) composites fabricated by one-step reactive spark plasma sintering

A dense HfC(Si, O)-HfB₂(Si, O) composite was fabricated by reactive spark plasma sintering using HfC and SiB₆ as starting reactants. The best ablation resistance was obtained with the composite fabricated with the addition of 15 vol.% SiB₆. After ablation under an oxyacetylene flame for 60 s, the mass and linear ablation rates of this composite were ?0.007 mg cm^?2 s^?1 and ?0.233 μm s^?1, respectively. The negative ablation rates are the result of a slight mass gain/thickness increase, which indicate that the oxidation process was stable and mechanical scouring was limited during ablation. This enhanced ablation resistance was attributed to a unique double-layered oxide formation, which possessed lower oxygen permeability and better mechanical strength. The solid solution nature of the composite and its appropriate phase composition were responsible for the stable oxide structure formation.     

Oxidation resistance of tantalum carbide-hafnium carbide solid solutions under the extreme conditions of a plasma jet

The oxidation behaviors of tantalum carbide (TaC)- hafnium carbide (HfC) solid solutions with five different compositions, pure HfC, HfC-20 vol% TaC (T20H80), HfC- 50 vol% TaC (T50H50), HfC- 80 vol% TaC (T80H20), and pure TaC have been investigated by exposing to a plasma torch which has a temperature of approximately 2800 °C with a gas flow speed greater than 300 m/s for 60 s, 180 s, and 300 s, respectively. The solid solution samples showed significantly improved oxidation resistance compared to the pure carbide samples, and the T50H50 samples exhibited the best oxidation resistance of all samples. The thickness of the oxide scales in T50H50 was reduced more than 90% compared to the pure TaC samples, and more than 85% compared to the pure HfC samples after 300 s oxidation tests. A new Ta₂Hf₆O₁₇ phase was found to be responsible for the improved oxidation performance exhibited by solid solutions. The oxide scale constitutes of a scaffold-like structure consisting of HfO₂ and Ta₂Hf₆O₁₇ filled with Ta₂O₅ which was beneficial to the oxidation resistance by limiting the availability of oxygen.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Effect of processing parameters on microstructure and ablation behavior of SiC/ZrB2 coating for graphite

In this research, a SiC/ZrB₂ coating was produced on graphite by reactive melt infiltration and plasma spraying method. The coating characterization was performed using XRD analysis, electron microscopy equipped with energy dispersive spectrometer (EDS), and supersonic flame ablation test at 2073 K. The results indicated that the dense C/SiC coating with good ablation resistance can be obtained at 1873 K. The coating thickness decreased with increasing infiltration temperature. The results of ablation test showed that by increasing the infiltration temperature and holding time, weight loss and mass ablation rate decreased from 22.63% to 9.83% and 3.63 × 10⁻³ g cm⁻² s⁻¹ to 1.34 × 10⁻³ g cm⁻² s⁻¹, respectively. The results showed that by using the ZrB₂ as outer coating the ablation resistance improved remarkably. The weight loss and mass ablation rates for the SiC/ZrB₂ coating were 12.79% and 1.857 × 10⁻³ g cm⁻² s⁻¹, respectively.     

Nanosized Hf6Ta2O17 particles reinforced HfC ceramic coating for high temperature applications

There is an urgent need for the thermal protection of carbon/carbon composites to increase their service span in aerospace field. As members of ultra-high temperature ceramics, HfC and ZrC are thought to be alternative materials, but their poor oxidation behavior and fracture toughness at temperature over 2000 ℃ prevent them from taking full advantages. Herein, we synthesized nanosized Hf₆Ta₂O₁₇ powders and introduced them into HfC ceramic to tackle the above problems. Plasma-sprayed HfC coatings with Hf₆Ta₂O₁₇ varied from 0 to 15 mol.% (0, 1.25, 2.5, 5, 15) were exposed to an oxyacetylene torch with a heat flux of 2.38 MW/m². The one with 2.5 mol.% Hf₆Ta₂O₁₇ showed the best ablation resistance. Smaller doping was unable to effectively hinder oxygen diffusion given the inadequate compactness of the formed scale, conversely substantial humps and ruptures formed on the samples with higher amounts, acting as straightforward paths for oxygen.     

Ablation behavior and mechanism of Cf/SiBCN composites in plasma ablation flame

In this work, C_f/SiBCN composites are fabricated by an improved precursor infiltration and pyrolysis (PIP) approach. Ablation behavior of the C_f/SiBCN composites is investigated in plasma ablation flame at a heat flux of 4.02 MW m⁻², which provides a quasi-real hypersonic service environment at a temperature up to 2200°C. After ablation, the ablated surface is covered with oxidation products in the form of oxide layer, fibrous residues, or bubbles, which effectively isolates the sample surface from the plasma flame and inhibits the scouring of high-speed flame to the composites. As a result, the C_f/SiBCN composites present an excellent ablation-resistant property, with linear and mass recession rates as low as 0.0030 mm s⁻¹ and 0.0539 mg mm⁻² s⁻¹, respectively. It is also revealed that the material at ablation center undergoes crystallization and oxidation processes during ablation, while the ablation behavior at transition area and ablation fringe only contains oxidation process due to the local temperature difference. Si₃N₄ and SiC grains are precipitated from amorphous SiBCN matrix during the crystallization process, and the oxidation process mainly involves the oxidation of carbon fiber and SiBCN matrix, etc.     

Long-term oxidation and ablation behavior of Cf/ZrB2–SiC composites at 1500, 2000, and 2200°C

Although C_f/ZrB₂–SiC composites prepared via direct ink writing combined with low-temperature hot-pressing were shown to exhibit high relative density, high preparation efficiency, and excellent flexural strength and fracture toughness in our previous work, their oxidation and ablation resistance at high and ultrahigh temperatures had not been investigated. In this work, the oxidation and ablation resistance of C_f/ZrB₂–SiC composites were evaluated via static oxidation at high temperature (1500°C) and oxyacetylene ablation at ultrahigh temperatures (2080 and 2270°C), respectively. The thickness of the oxide layer of the C_f/ZrB₂–SiC composites is <40 μm after oxidizing at 1500°C for 1 h. The C_f/ZrB₂–SiC composites exhibit non-ablative properties after oxyacetylene ablation at 2080 and 2270°C for >600 s, with mass ablation rates of 3.77 × 10⁻³ and 5.53 × 10⁻³ mg/(cm² s), and linear ablation rates of −4.5 × 10⁻⁴ and −5.8 × 10⁻⁴ mm/s, respectively. Upon an increase in the ablation temperature from 2080 to 2270°C, the thickness of the total oxide layer increases from 360 to 570 μm, and the carbon fibers remain intact in the unaffected region. Moreover, the oxidation and ablation process of C_f/ZrB₂–SiC at various temperatures was analyzed and discussed.     

Polymer-metal slurry reactive melt infiltration: A flexible and controllable ceramic modification strategy for irregular C/C components

Herein, we investigate the applicability of the polycarbosilane (PCS)–metal slurry reactive melt infiltration (RMI) process to various metals. The slurry exhibiting the best ceramized ability was used to examine the relationship between the ceramic thickness and reactive time, ceramic thickness and reactive temperature, and infiltration depth and slurry-coating thickness. The results show that the thickness of the ceramic layer increases with reactive time and temperature and the infiltration depth increases with the coating thickness. PCS–Si₉₀Zr₁₀ slurry RMI was selected to modify cylindrical nozzle C/C preforms, and dense C/C–SiC–ZrC composites with a density of ~2.05 g cm⁻³ were obtained. Owing to the good control of the PCS–Si₉₀Zr₁₀ slurry RMI on the interface, matrix, and carbon fiber of the as-received cylindrical composites, the bending strength of the C/C–SiC–ZrC composites was as high as 306.4 MPa, which is considerably higher than that of a C/C preforms (70.4 MPa). Considering the ablation resistance, the mass and linear ablation rates of the C/C–SiC–ZrC composite (~0.29 mg s⁻¹ and ~2.48 × 10⁻³ mm s⁻¹, respectively) were similar to those of the composites prepared using traditional RMI (~0.23 mg s⁻¹ and ~2.29 × 10⁻³ mm s⁻¹). The proposed polymer–metal RMI is more suitable for the modification of C/C preforms with thin-wall structures owing to its advantages including precise control of infiltration dose and flexible operation of slurry coating. Furthermore, it is suitable for the local modification of C/C components.     

High fracture toughness of HfC through nano-scale templating and novel sintering aids

An approach to improve the sintering ability and the fracture toughness of hafnium carbide (HfC) ceramic by designing a unique composite structure is reported. The uniform and ultra-fine HfC nanoparticles (~300 nm) are synthesized at 1450°C by vacuum carbonization reaction with the glucose-derived hydrothermal precursor as a carbon source and template. HfC ceramic sintered with a SiCN sintering aid of 15 vol. % possesses a beneficial three-dimensional network microstructure composed of inter-penetrating phases of carbon, SiC and HfC with varied stoichiometry at multi-length scales. The obtained HfC exhibits a higher fracture toughness of 5.5 MPa m^1/2, which can be attributed to the unique composite structure able to promote stress releases in the crack tip and enhance the resistance to crack propagation.     

Ablation resistance of HfC coating reinforced by HfC nanowires in cyclic ablation environment

To improve the ablation resistance of carbon/carbon composites in cyclic ablation environment, SiC/HfC ceramic coating reinforced by HfC nanowires was prepared. The microstructure, bonding strength, coefficient of thermal expansion and cyclic ablation resistance of the as-prepared coating were investigated. After incorporating HfC nanowires, the bonding strength between inner SiC coating and outer HfC coating was increased. HfC nanowires could relieve the coefficient of thermal expansion mismatch between inner and outer coating and improve the toughness of the outer coating. By introducing HfC nanowires, the coated sample’s cyclic ablation resistance was improved. After cyclic ablation under oxyacetylene flame for 60 s × 3, the mass and linear ablation rates of the coated sample with HfC nanowires were only 0.444 mg/s and −0.767 μm/s, respectively.     

Effects of Si3N4 and WC on the oxidation resistance of ZrB2/SiC ceramic tool materials

ZrB₂/SiC, ZrB₂/SiC/Si₃N₄ and ZrB₂/SiC/WC ceramic tool materials were prepared by spark plasma sintering technology, and their oxidation resistance was tested at different oxidation temperatures. When the oxidation temperature is 1300 °C, the oxide layer thickness, oxidation weight gain and flexural strength of ZrB₂/SiC/Si₃N₄ ceramic tool material after oxidation are 8.476 μm, 1.436 mg cm^?2 and 891.0 MPa, respectively. Compared with ZrB₂/SiC ceramic tool materials, the oxide layer thickness and oxidation weight gain are reduced by 8.2% and 11.8%, respectively, and the flexural strength after oxidation is increased by 116.1%. However, the addition of WC significantly reduces the oxidation resistance of the ceramic tool material. A dense oxide film is formed on the surface of ZrB₂/SiC/Si₃N₄ ceramic tool material during oxidation, which effectively prevents oxygen from entering the inside of the material, thereby improving the oxidation resistance of the ceramic tool material.     

Ultra-high-temperature ablation behavior of SiC–ZrC–TiC modified carbon/carbon composites fabricated via reactive melt infiltration

To improve the ablation resistance under the ultra-high temperature, the matrix of the carbon/carbon (C/C) composite was modified with a ternary ceramic of SiC–ZrC–TiC via reactive melt infiltration. The obtained ceramic matrix was composed of Zr-rich and Ti-rich solid solution phases of Zr_1−xTi_xC and SiC. This composite exhibited an excellent ablation property at 2500 °C with low mass and linear ablation rates of 0.008 mg s⁻¹ cm⁻² and 0.000 μm s⁻¹, respectively. The ablation mechanism was revealed with various microstructure characterizations and compared with those of C/C–SiC and C/C–TiC composites. Results showed that the degradations of these composites were primarily caused by the loss of the protective oxide scale via volatilization under the ultra-high temperature and flushing by high-speed airflow. The high ablation resistance of the C/C–SiC–ZrC–TiC composite was attributed to the protection of a multiphase oxide scale with high viscosity and low volatility.     

Ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide and (Hf–Ta–Zr–Nb–Ti)C–xSiC composites

The ablation behavior of (Hf–Ta–Zr–Nb–Ti)C high-entropy carbide (HEC-0) was investigated using a plasma flame in air for different times (60, 90, and 120 s) at about 2100°C. The effect of SiC content on the ablation resistance of HEC–xSiC composites (x = 10 and 20 vol%) was also studied. The linear ablation rate of HEC-0 decreases with increasing ablation time, showing the positive role of the oxide layer with a complex composition. The linear ablation rate of HEC–10 vol% SiC (0.3 µm s⁻¹) is only a 10th of that of HEC-0, showing a significant improvement in ablation resistance, probably due to the formation of a protective oxide layer containing melted SiO₂ and refractory Hf–Zr–Si–O oxides.     

Oxidation and ablation behaviour of multiphase ultra-high-temperature ceramic Ta0·5Zr0·5B2–Si–SiC protective coating for graphite

To provide reliable oxidation protection for carbon materials under harsh high-temperature aerobic environments, a dense monolayer-multiphase ultra-high-temperature ceramic Ta_0·5Zr_0·5B₂–Si–SiC (TZSS) coating was fabricated by a combination of dipping and in-situ reaction. The oxidation resistance of the TZSS coating was investigated at 1923 K in air. The results indicated that the TZSS coating could offer at least 70 h of oxidation protection for the matrix material. The synergistic oxygen-blocking effect of the thick oxide layer formed during the oxidation test and the inner coating, played a key role in the oxidation protection process. These were responsible for the excellent oxidation resistance ability of the TZSS coating. Additionally, the ablation performance of the TZSS coating was also investigated under increased heat flux from 2.4 MW/m² to 4.2 MW/m². The ablation behaviours changed from the oxidation and evaporation of coating materials to mechanical scouring, corresponding to increased mass and linear ablation rates. Interestingly, after ablation for 40 s under a heat flux of 4.2 MW/m², a new microstructure composed of “lath-like” Ta₄Zr₁₁O₃₂ solid solution grains was found in the ablation center. This oxide layer possessed few micropores, which could provide reliable protection for the matrix material under ultra-high-temperature oxygen-containing airflow erosion, thus preventing further damage to the composite.     

The Oxidation of Coated SOFC Interconnects in Fuel Side Environments

This study focuses on examining the effect of PVD coatings on the oxidation performance of interconnects in fuel (anode) side environments. A Fe‐22Cr ferritic steel was coated with (i) Ce 10 nm (ii) La 10 nm and (iii) Co 600 nm. The samples were exposed at 850 °C in Ar‐5% H₂‐3% H₂O in a tubular furnace over 500 h. Additionally, the effect of a pre‐oxidation step was investigated by exposure in air prior to the simulated fuel gas environment. Chemical analysis on the samples was subsequently performed with SEM/EDX and XRD. It was established that the Ce and La coatings brought about a factor 2–3 reduction (k_p values of 2.16 × 10⁻¹⁴ ± 3.6 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹ for the La 10 nm coated steel compared to 7.72 × 10⁻¹⁴ ± 5.86 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹ for the uncoated steel) in the oxidation rate while the Co coating disintegrated into metallic islands in and on the thermally grown oxide after exposure. Additionally, the La coating resulted in the formation of a continuous perovskite layer by reaction with the thermally grown oxide.     

Thermal,mechanical and electrical properties of hard B4C,BCN, ZrBC and ZrBCN ceramics

We study the thermal, mechanical and electrical properties of B₄C, BCN, ZrBC and ZrBCN ceramics prepared in the form of thin films by magnetron sputtering. We focus on the effect of Zr_x(B₄C)_1−x sputter target composition, the N₂+Ar discharge gas mixture composition, the deposition temperature and the annealing temperature after the deposition. The thermal properties of interest include thermal conductivity (observed in the range 1.3–7.3 W m⁻¹ K⁻¹), heat capacity (0.37–1.6×10³ J kg⁻¹ K⁻¹ or 1.9–4.1×10⁶ Jm⁻³ K⁻¹), thermal effusivity (1.6–4.5×10³ J m⁻² s^−1/2 K⁻¹) and thermal diffusivity (0.38–2.6×10⁻⁶ m² s⁻¹). We discuss the relationships between materials composition, preparation conditions, structure, thermal properties, temperature dependence of the thermal properties and other (mechanical and electrical) properties. We find that the materials structure (amorphous×crystalline hexagonal ZrB₂-like×nanocrystalline cubic ZrN-like), more than the composition, is the crucial factor determining the thermal conductivity and other properties. The results are particularly important for the design of future ceramic materials combining tailored thermal properties, mechanical properties, electrical conductivity and oxidation resistance.     

Mechanical,electrical and thermal properties of HfC-HfB2-SiC ternary eutectic composites prepared by arc melting

HfC-HfB₂-SiC composites were prepared by arc melting using HfC, HfB₂ and SiC powder as raw materials. The ternary eutectic composition of 16HfC-17HfB₂-67SiC (mol%) was first identified, showing a complicated maze microstructure of HfC, HfB₂ and SiC approximately 500 nm in thickness. The eutectic temperature of the HfC-HfB₂-SiC composite was nearly 2760 K. The Vickers hardness and fracture toughness of the HfC-HfB₂-SiC ternary eutectic composite were 20.8 GPa and 7.7 MPa m^1/2, respectively. With increasing temperature from 300 to 800 K, the electrical conductivity decreased from 8.8 × 10⁵ to 4.3 × 10⁵ Sm⁻¹, whereas the thermal conductivity increased from 28 to 32 W m⁻¹ K⁻¹.     

SiCN ceramics with controllable carbon nanomaterials for electromagnetic absorption performance

Different kinds of carbon nanomaterials, free carbon (C_free), graphene, and N-containing graphene (NG), in single-source-precursors-derived SiCN ceramics, were in situ generated by modifying polysilazane with divinylbenzene, dopamine hydrochloride and melamine, respectively. Adjusting the carbon source brings phase structure and electromagnetic wave absorption (EMA) properties differences of SiCN/C ceramics. In situ C_free enhances the EMA capacity of SiCN ceramics by improving their electrical conductivity of 9.2 × 10⁻⁴ S/cm. The electrical conductivity of SiCN ceramics with 2D graphene sheets balloons to 2.5 × 10⁻³ S/cm, causing poor impedance match thus leading to a worse EMA performance. In situ NG in SiCN ceramics has a low electrical conductivity of 5.6 × 10⁻⁸ S/cm, making for excellent impedance match. The corrugated NG boosts dielectric loss, interfacial, and dipole polarization. NG-SiCN nanocomposites possess an outstanding EMA performance with RL_min of −61.08 dB and effective absorption bandwidth of 4.05 GHz, which are ∼2.4 times lower and ∼4 times higher than those of SiCN, respectively.     

High temperature oxidation behavior of porous MoAlB ceramic from 800 °C to 1100 °C in air

MoAlB possesses the characteristics of both metals and ceramic materials, which has attracted extensive attention due to its excellent high-temperature oxidation resistance. For this reason, porous MoAlB is considered applicable to the practice of filtration under harsh environment. In this study, the high-temperature oxidation behavior of porous MoAlB ceramics is systematically studied at the temperatures ranging from 800 to 1100 °C. According to the results, the porous MoAlB exhibits good oxidation resistance at a maximum temperature of 1000 °C. The oxidation kinetics of porous MoAlB can be divided into three stages, and the estimated activation energies of the three stages are 253.83 kJ·mol⁻¹, 367.48 kJ·mol⁻¹ and 317.84 kJ·mol⁻¹, respectively. In the stable stage at 1000 °C, the quadratic mass gain per unit area shows linearity over time, and the oxidation rate of porous MoAlB reaches 37.31 mg²·cm⁻⁴·h⁻¹. As revealed by the analysis of the composition and microstructure of oxide layers, the main components of the oxide layer include MoO₃, MoO₂, Al₂O₃, B₂O₃. With the extension of oxidation time, the content of Al₂O₃ in the oxide films increases. The average pore size, permeability and open pore porosity of porous MoAlB show a trend of first decreasing and then tending to be stable. In addition, a discussion is conducted on the high-temperature oxidation mechanism of porous MoAlB.