Ultra-high Temperature Ceramics Research Articles

High strain rate response and mechanical performance of tantalum carbide–hafnium carbide solid solution

Ultra-high temperature ceramics (UHTCs) based on the solid solution TaxHf1-xC have shown great promise as materials for extreme environments (>2500 °C) due to their improved thermo-mechanical properties. However, their dynamic response under high-impact loading remains unknown. In this study, we investigate the dynamic impact behavior and fracturing evolution of TaxHf1-xC samples (with x = 0, 0.2, 0.5, 0.8, and 1) at a strain rate > 103 s-1 using the Split Hopkinson Pressure Bar (SHPB) test. Among the different compositions, Ta0.5Hf0.5C exhibits the highest compressive strength of 1870 MPa, representing a 36% improvement over TaC and 54% over HfC. High frame rate videos and deformation analysis reveal that Ta0.5Hf0.5C, characterized by extensive Ta–Hf bonding, significantly reduces the crack propagation rate by approximately 1435% compared to TaC and 4050% compared to HfC. This effect is attributed to the dislocation pile-ups, nano-twin formation, inter grain twisting exhibited mostly along {111} plane as Hf substitutes Ta in TaxHf1-xC samples. Further, the surface energy is least for {111} plane eliciting the higher probability for bypassing crack propagation along this plane in TaxHf1-xC. The exceptional damage tolerance and improved mechanical properties of Ta0.5Hf0.5C, compared to other solid-solution TaxHf1-xC compositions, make it an extraordinary structural material for hypersonic applications. These findings provide valuable insights into the dynamic behavior of UHTCs and highlight the potential of Ta0.5Hf0.5C as a superior material for extreme environments requiring high-impact resistance.

Numerical assessment of ceramic micro heat exchangers working with nanofluids by Taguchi optimization approach

The rapid advancements in microsystems technology have necessitated the exploration of innovative materials for efficient thermal management in micro heat exchangers. This research delves into the performance evaluation of three ultra-high temperature ceramics (UHTCs): ZrB2, BeO, and Si3N4 as alternative micro heat exchanger fabrication materials. The study systematically assessed the ceramics' interaction with Al2O3-nanofluids across diverse volume percentages and mass flow rates using the Taguchi optimization method. Beryllium oxide (BeO) emerged as the superior material, registering warm outlet temperatures as low as 64.86°C and cold outlet peaks at 31.68°C. Sensitivity analyses further underscored the critical role of inlet temperature on outlet dynamics, with warm and cold outlets showing significances of ~72% and ~99%, respectively. Additionally, the research pinpointed 0.75 vol% as the optimal Al2O3-nanofluid concentration, yielding the most favorable performance metrics across the ceramics.

Phase composition, densification behavior and high-temperature strength of carbon-doped ZrB2–ZrSi2 ceramics

Sintering additive of ZrSi2 is beneficial to low-temperature densification of ZrB2-based ultra-high temperature ceramics (UHTCs), nevertheless, residual ZrSi2 would severely reduce the high-temperature strength of UHTCs. In the current work, to achieve low-temperature preparation of ZrB2-based UHTCs with good high-temperature strength, active carbon (C) was added into ZrB2–ZrSi2 ceramics to convert the sintering additive into refractory phases of SiC/ZrC. C-doped ZrB2–ZrSi2 powders were hot-pressed at different temperatures to investigate the phase composition, microstructure and densification behavior. TG-DSC, XRD and SEM results indicated that ZrSi2 was almost entirely converted into SiC and ZrC at 1600 °C for 2h, meanwhile, a fully-dense C-doped ZrB2–ZrSi2 ceramic was obtained at such sintering conditions. In addition, the high-temperature (1800 °C) strength of C-doped ZrB2–ZrSi2 ceramic was 390 ± 21 MPa, which was much higher than that of the C-undoped one. The excellent high-temperature mechanical properties could be attributed to the transformation of low-melting-point phases into refractory phases.

Single-stage reaction hot pressing route for dense refractory high entropy TiZrHfVNbTaB12-C ceramic composite

Hot pressing reaction-assisted sintering of novel refractory ceramic composite TiZrHfVNbTaB12-C was undertaken. The sintered material belongs to the class of Ultra-High-Temperature Ceramics (UHTCs). The sintering was done by utilizing transitional metal carbides and B4C at 1950 °С and 30 MPa for 8 min in a graphite die within an argon atmosphere. The ceramic demonstrated 98% density as measured by Archimedes’ method with accounted ceramic contamination by ZrO2 during initial carbide milling. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) revealed a single multimetal boride phase with AlB2-type (hexagonal, P6/mmm) structure and carbon inclusions. It is thought that the high concentrations of transitional metals lead to high configurational entropy effects and this produces a single boride phase. On those grounds, the ceramic belongs to the class of High Entropy Ceramics (HECs). The composite Vickers’ hardness HV was 12 ± 1 GPa and indentation toughness K1C was 4.3 ± 0.3 MPa·m1/2.

Unveiling the wear behavior of multi-component ultra-high temperature ceramic thin coatings with pulsed electro-spark deposition

The study presents a novel approach using pulsed electro-spark deposition (PED) to apply a thin protective coating of multi-component ultra-high temperature ceramics (MC-UHTCs) on a steel substrate. A single solid-solution phase of (TaNbHfTi)C-based MC-UHTC electrode is prepared using spark plasma sintering (SPS). The coating process involves melting, rapid re-solidification, and forming nano-grains (15–20 nm) resembling splash-like features. MC-UHTC coating remains stable without oxidation and any phase transformation. The bonding between the coating and the substrate is strong, regardless of the coating thickness, which can vary from <1 μm to over 25 μm. Scratch testing along the interface demonstrates that the MC-UHTC coating exhibits improved wear resistance compared to the uncoated steel substrate. This improvement is attributed to the significantly higher hardness of the coating, which is up to 4.5 times greater than substrate. The dominant wear mechanisms observed include plowing in the substrate, micro-cracking at the interface, lateral cracking and brittle fracture in the MC-UHTC coating. Overall, this study presents promising opportunities for developing innovative protective MC-UHTC coatings without needing expensive environmental chambers while preserving their chemical functionality. By employing the PED technique and utilizing MC-UHTCs, the wear resistance of structural metallic components can be enhanced effectively.

Structural stability, hardness, fracture toughness and wear resistance of refractory metal carbonitrides RMC1-xNx (RM = Zr, Nb, Hf, Ta) solid solutions from first-principles calculations

With the rapid development of aerospace field, ultrahigh temperature ceramics are required to have excellent mechanical properties in harsh environment, thus refractory metal carbonitrides have attracted much attention. In this work, the formation energy, lattice constant, volume, elastic constants, elastic modulus, hardness, fracture toughness, wear resistance, and density of states of refractory metal carbonitrides RMC1-xNx (RM = Zr, Nb, Hf, Ta) solid solutions have been systematically calculated by first-principles calculations. The formation energy results indicate that the stability of the RMC1-xNx increased with the increases of composition x, and the HfC1-xNx was the most stable at the same composition. The calculated lattice constant and volume of RMC1-xNx always decrease with the increase of N composition x, which also suggests that the stability of RMC1-xNx gradually increases. The RMC1-xNx solid solutions are mechanically stable. Furthermore, the addition of nitrogen could improve the brittleness and bulk modulus of the RMC1-xNx solid solutions. The impurity of nitrogen could enhance the fracture toughness of ZrC1-xNx and HfC1-xNx solid solutions. The calculated hardness and wear resistance of ZrC1-xNx and HfC1-xNx solid solutions firstly increase, and subsequently decrease with increasing N composition x. Finally, the results of the density of states also indicate that the stability of the RMC1-xNx increased with increasing N composition, which are also consistent with the energy results. In a word, our results are helpful for the design of metal carbonitride based ultrahigh temperature ceramics.

Accelerated discovery of oxidation-resistant ultra-high temperature ceramics via data driven methodology

To accelerate the discovery of ultra-high temperature ceramics (UHTCs) with excellent oxidation resistance at high temperatures, this paper is the first attempt to apply a high-throughput experiments (HTEs) assisted data-driven strategy in the prediction of oxidation recession of transition metal diboride-SiC ceramic composites. The data generated by HTEs enables us to apply the machine learning (ML) method in discovering novel oxidation-resistant UHTCs. Artificial Neural Network (ANN) and Kernel logistic regression (KLR) models show an outstanding performance against other ML models. Optimum compositions with exceptional oxidation resistance were rapidly observed using the trained KLR model.

Microwave sintering of ZrB2-based ceramics: A review

Recently, microwave sintering has absorbed remarkable attention on the basis of enhanced microstructural/mechanical characteristics in comparison with conventional sintering techniques based on powder technology. This method not only can be employed for the processing of metals, alloys, and metal matrix composites but also for the manufacturing of advanced ceramics and ceramic matrix composites. Zirconium diboride (ZrB2) as an interesting member of ultrahigh temperature ceramics is one of the most undertaking candidates in modern structural ceramics applications. This paper reviews the processing-densification-mechanical properties correlations in microwave-sintered ZrB2-based ceramics and composites. The text concentrates on the microwave-assisted production of ZrB2 divided into two categories: synthesis of ZrB2 powders by microwave sintering and sintering of ZrB2-based ceramics and composites by microwave sintering. The effects of some additives and reinforcements, such as B4C, SiC, TiC, and MgO, on zirconium diboride's densification and mechanical properties are summarized.

Controlled nitrogen content synthesis of hafnium carbonitride powders by carbonizing hafnium nitride for enhanced ablation properties

In this study, a new method of carbonizing hafnium nitride was proposed to synthesize ultrahigh-temperature hafnium carbonitride (HfCxNy) powders. The new method helps to maintain both the purity of phases and control the content of nitrogen in the HfCxNy. The results show that the as-prepared HfCxNy powders have a single phase, with an average particle size of approximately 2 μm, and Hf, C and N are evenly distributed. Moreover, the microstructures, phase compositions, ablation properties and mechanism of the HfC0.62N0.38 composites under a plasma ablation environment were studied in detail. The results show that the HfC0.62N0.38 composites exhibited excellent ablation resistance at 3073 K for 60 s and the ablation mechanism of HfC0.62N0.38 can be identified as HfC0.62N0.38→HfCxOy→HfO2. The mass ablation rate of the HfC0.62N0.38 composite is evaluated to be 1.36 mg/cm2∙s, which is lower than that of HfC ceramics. Our work is intended to provide new insight regarding the development of ultrahigh-temperature ceramics and widen their applications.

PRODUCING METHOD OF HIGH ENTROPY CARBIDE IN AN IONIC MELT

Refractory metal carbides TiC, ZrC, HfC, NbC and TaC have excellent physical, chemical and mechanical properties as materials for ultra-high temperature ceramics. Of these, the most refractory are TaC and HfC, whose melting points approach 4000°C. It should be noted the high hardness, strength and wear resistance of refractory carbides. Hence, there is a natural interest in high-entropy carbides based on them, which are becoming an important class of new ceramic materials, since they potentially have more advanced applied properties. However, obtaining such materials by classical metallurgical methods is a difficult task. In modern research, samples of high-entropy carbides are most often synthesized using expensive special equipment (methods of plasma-spark sintering, high-energy planetary mills, etc.) and a relatively long preparation of precursors for sample production. This paper describes a new approach to the synthesis of multicomponent carbide (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C using an electrochemical process at a temperature not exceeding 1173 K. The method is based on the phenomenon of currentless metal transfer in molten salts. After the step-by-step transfer of metals, the sample was washed from the electrolyte, then sintered in a vacuum furnace. According to X-ray phase analysis, the resulting high-entropy carbide is a single-phase solid solution with an FCC structure. The diffraction pattern of the synthesized sample is in good agreement with the calculated diffraction pattern obtained by the Debye formula for a supercell of 64 000 atoms. A compact sample of high-entropy carbide was produced by pressing a tablet 10 mm in diameter with the addition of cobalt as a matrix metal. After vacuum sintering, the sample was ground to prepare for examination on a scanning electron microscope. Elemental mapping of the sample surface was performed, which showed a satisfactory distribution of metals that make up the high-entropy carbide. The measured microhardness of the sample turned out to be less than the values found in the publications of other authors, which may be due to some residual sample porosity.

Microstructural characterization of ZrB2–SiC–Si–MoSi2–WC coatings applied by SPS on graphite substrate

The aim of this research was to apply a protective composite coating made of ultra-high temperature ceramics (UHTCs) on the graphite substrates. The spark plasma sintering (SPS) method was used to apply this coating on the graphite substrate. First, efforts were made to choose the right chemical composition for the composite material of the coating and the sintering conditions (temperature, pressure, and holding time) for applying the coating. Then, single-layer coatings with the basic composition of ZrB2–SiC–Si with WC and MoSi2 additives in equal amounts of 1.25 and 3.75 vol% of each were successfully applied on the graphite substrates under sintering conditions of 1875±25 °C final temperature, 10 MPa initial pressure, 25 MPa final pressure and 5 min holding time. The presence of the Si element in the basic composition of these coatings, in addition to helping to form an intermediate diffusion layer at the interface between the composite coating and the graphite substrate, caused the strengthening of the joining despite the difference in the coefficient of thermal expansion between the graphite and the composite coating.

Sensitivity analysis of fluid flow parameters on the performance of fully dense ZrB2-made micro heat exchangers

Heat exchangers are important in modern technology and are used in various industries such as power plants, automobiles and airplanes. Their main role is to ensure efficient heat transfer tailored to specific system needs. With miniaturized electronics, challenges such as circuit overheating have emerged, increasing the demand for compact yet high-performance heat exchangers. The advent of micro-electromechanical systems has increased the application of micro heat exchangers with their high surface-to-volume ratio promising enhanced efficiency. Although metals such as aluminum are commonly used for fabricating heat exchangers, their susceptibility to corrosion and high temperatures limits their usefulness. This study turns attention to ultrahigh temperature ceramics, specifically fully sintered ZrB2, known for their high temperature durability and oxidation resistance. Utilizing the Taguchi approach, a robust optimization method, this study explores the sensitivity analysis of fluid flow parameters on the performance of fully dense ZrB2-made micro heat exchangers and highlights the potential of ceramics in heat exchanger construction. Based on the results, the mass flow rate with an estimated contribution of 4.4% in the effectiveness is the most influential parameter on the performance, and in the best case, the effectiveness reaches 24.3%.

Effects of oxidation on the effective thermomechanical properties of porous ultra-high temperature ceramics in compression via computational micromechanics and MPM

Due to the harsh flight environment of hypersonic platforms, Ultra-High Temperature Ceramics (UHTCs) imbued with macroscale porosity have been introduced as candidates for providing thermal insulation of sensitive on-board components. This study employs an oxidized state approach for modeling the coupled effects of surface oxidation and continuum damage in the effective thermomechanical response of such materials within the framework of computational micromechanics. Using an in-house Material Point Method (MPM) computational tool, two-dimensional plane strain simulations were performed on representative hexagonal structures of TiB2 with 10%, 40% and 70% macroporosity. Oxide layers ranging from 5 to 50 μm were applied to the structures in place of a transient, diffusion-based oxidation solver. Simulations with applied compressive strains of up to 30% were then performed on hexagonal structures with and without the oxide layer present. A range of dynamic thermal gradients were also applied to investigate the damage due to thermal expansion coefficient mismatch. Finally, the oxidized state modeling approach was applied to large porous structures derived from micro computed tomography images of TiB2 foam.

Effects of high thermal conductivity chopped fibers on ablation behavior of pressureless sintered SiC–ZrC ceramics

As one of the most promising thermal protection materials, the ablation performance of SiC–ZrC ceramics is strongly influenced by thermal conductivity. In this work, the high thermal conductivity mesophase pitch-based carbon fibers (MPCFs) were uniformly added into a mixture of SiC and ZrC powders, which were pressureless sintered to form a MPCFs modified SiC–ZrC ceramics. The relationship between thermal conductivity and MPCFs content was investigated in detail. Both theoretical calculations and experimental results showed that the SiC–ZrC ceramics modified by adding 4.81 vol% MPCFs gained the highest thermal conductivity of 68.10±0.68 W/(m⋅K). The simulation shows that the temperatures at ablation center and backside of the ceramics were 1094 °C and 446 °C, respectively, after plasma ablation at 2300 °C for 20 s. And the actual backside temperature was detected to be 438 °C and that agreed with the simulation results. The high thermal conductivity leads to a lower ablation temperature because the heat is rapidly transferred from the high temperature part to the low region. Due to the low ablation temperature, the 4.81 vol% MPCFs modified SiC–ZrC ceramics exhibited the lowest mass ablation rate (−0.048±0.007 mg/s) and linear ablation rate (−0.715±0.056 μm/s). This research presents a novel insight for designing and fabricating excellent ablation-resistance ultra-high temperature ceramics (UHTCs).

Mechanical properties and fracture behavior of ultrahigh temperature ceramics at ultrahigh temperatures

The mechanical properties of an ultrahigh temperature ceramic (UHTC) made up of ZrB2, SiC and graphite flake (ZrB2-SiC-G) are explored by ultrahigh-temperature uniaxial tension, combined with in-situ monitoring of the fracture behavior. The results suggest an inconsistent property degradation of ZrB2-SiC-G at 1200–2000 °C. Significant degradation in tensile modulus is observed at 1400 °C, which differs from the strength degradation that mainly occurs at 1800 °C. Moreover, ZrB2-SiC-G is elastically fractured at 1200 °C, 1400 °C and 1600 °C, which is interrupted at 1800 °C and 2000 °C. At the temperature range, severe plasticity takes place, which reduces the bearing capacity of this material. The brittle-to-ductile transition is well ascertained by in-situ observation of the fracture behavior at 1200–2000 °C. Finally, the constitutive relation of modulus and strength is built by coupling the effect of temperature. It can be integrated in finite element models and is useful for structural design of UHTC based thermal protection systems of hypersonic vehicles.

A novel Hf0.75Zr0.25N solid solution coating with high mechanical strength: Ablation protection application above 2200°C

Obtaining coatings with excellent ablation resistance is a longstanding challenge for the ablation protection of carbon/carbon (C/C) composites. In this work, a single phase Hf0.75Zr0.25N solid solution ultra-high temperature ceramic (UHTC) coating was proposed, and prepared on the surface of C/C composites by chemical vapor deposition (CVD) for the first time. The results revealed that the hardness and Young's modulus of Hf0.75Zr0.25N coating are higher than those of HfN and ZrN coatings, reaching 33.35 GPa and 316.42 GPa, respectively. After ablation for 180 s under oxygen acetylene flame with a temperature exceeding 2200 °C, the Hf0.75Zr0.25N coating retained its structural integrity and exhibited lower ablation (Rm: 0.26 mg/s; Rh: 0.32 μm/s). This is mainly attributed to the formation of the dense Hf-Zr-O oxide scale promoted by the oxidation sintering reaction during ablation. The above results indicate the nitride solid solution UHTC has great potential as ablation resistance coating at ultra-high temperatures.

Oxygen barrier resistance of HfB2-MoSi2-TaB2 coatings in a wide temperature region

HfB2-MoSi2-based ultra-high temperature ceramic (UHTC) coatings have shown remarkable antioxidant effects owing to the formation of silicate glass layers with low oxygen permeability in high-temperature environments, which shows great potential in the antioxidation of carbon structural materials. To further enhance the oxidation resistance of the HfB2-MoSi2-based coating in a wide temperature region, the influence of volume ratio between HfB2 and TaB2 on the antioxidant capacity of the HfB2-MoSi2-TaB2 coatings was investigated. The addition of 15 vol% TaB2 in the 60HfB2-40MoSi2 coating delays the initial oxidation temperature of the 60HfB2-40MoSi2 sample from 300 °C to 500 °C, which decreased the oxidation loss by 75.85% during dynamic oxidation. In oxidation process at 900 °C and 1700 °C, the weight gains of the 45HfB2-40MoSi2–15TaB2 coating reduced by 78.56% and 63.14%, respectively. Due to the coexistence of 45 vol%HfB2 and 15 vol%TaB2, the suitable Ta5+ promoted the homogenization and dispersion of Hf/Ta-oxides, which forms the coral-like Hf/Ta oxides skeleton in the glass layer, thus preventing the oxygen penetration and decreasing the inert factor of the HfB2-MoSi2 coating at 1700 °C by 51.19%. However, excessive TaB2 weakened the self-healing ability of the Ta-Hf-Si-O glass layer and inhibited the oxygen barrier effect of the HfB2-MoSi2-TaB2 coating.

Synthesis and Rapid Sintering of Ultra Fine TiB2-ZrO2 Composite

TiB2 is considered candidate materials for ultra-high temperature ceramics and cutting tools because of its a high thermal conductivity, a low coefficient of thermal expansion, a high hardness and high melting temperature. Despite these attractive properties, TiB2 applications are limited because it has a low fracture toughness below the brittle-ductile transition temperature. To improve on its mechanical properties, the approach universally utilized has been to add secondary materials to form a composite and to fabricate an ultra - fine material. A dense ultra - fine TiB2- ZrO2 composite was rapidly sintered using pulsed high current activated heating (PHCAH) methods within 3 min in one step from the mechanically synthesized the powders of TiB2 and ZrO2 . Consolidation was reached using an effective combination of mechanical pressure and the pulsed high current. A highly dense TiB2-ZrO2 material with relative density of 97.2% was made by the simultaneous application of 75 MPa pressure and a pulsed 2500 A current. The grain sizes of TiB2 and ZrO2 in the composite were 135 nm and 84 nm, respectively. The fracture toughness and hardness of the TiB2 -ZrO2 composite were 11.2 MPa.m1/2 and 957 kg/mm2 , respectively. The fracture toughness of the TiB2 -ZrO2 composite was three times higher than that of monolithic TiB2 .

Fabrication and investigation of novel hafnium-zirconium carbonitride ultra-high temperature ceramics

By a combination of mechanical activation, combustion synthesis, and spark plasma sintering methods, bulk materials in the Hf-Zr-C-N system with various Hf/Zr atomic ratios were produced. The mechanical activation process in a low-energy mode (350 rpm) for 90 min resulted in the formation of layered Hf/Zr/C composite particles 10–30 μm in size, depending on the Hf/Zr ratio. The diffraction spectra of the as-synthesized powders were described by several isomorphic (Hf,Zr)(C,N)ss cubic phases with different nitrogen content. Spark plasma sintering contributed to the homogenization of the chemical composition and allowed production of the dense (∼98%) single-phase hafnium-zirconium carbonitrides with an FCC structure. The bulk ceramics exhibited superior hardness (∼17 GPa) and fracture toughness (∼5 MPa m1/2), relative to (Hf,Zr)C carbides prepared by similar methods.

Exploring new solvent mixtures for near-net shaping of Ultra-High Temperature Ceramics via colloidal processing

Suspensions of Ultra-High Temperature Ceramic (UHTC) powder with various organic solvents and co-solvent mixtures were prepared with the intention of verifying and understanding the relationship between interparticle interactions, flow behavior, and resulting particle packing. These relationships can be used to predict optimal solvent choices in colloidal processing of UHTCs to guarantee suspension stability through an adequate balance of the interparticle forces in suspension. Four organic solvents were selected: cyclohexane (CYC), tetrahydrofuran (THF), acetone (ACE) and N,N-dimethylformamide (DMF). The theoretical performance of each suspension, based on interparticle interaction energies, was compared to the empirical results. Detailed flow behavior was studied through rheological measurements and particle packing was measured by Archimedes’ method. The relationship between interparticle forces, viscosity and particle packing is discussed. Other contributing factors such as the performance of the dispersing agent were also considered and surface characteristics were reported using X-ray Photoelectron Spectroscopy (XPS), providing a modification to the adsorption parameter in the repulsive model. Low viscosity slurries were obtained at approximately 40% solid loading. CYC and THF demonstrated the ability to be effective co-solvents and produce the highest suspension stability with 100% CYC. These findings will help to produce UHTC complex shape component with minimal flaws during processing that can withstand extreme, high temperature oxidizing environments after densification.