Ultra-high Temperature Ceramic Matrix Composites Research Articles

Paste extrusion‐based 3D printing of fiber‐reinforced ultra high‐temperature ceramics

AbstractUltra–high‐temperature ceramics (UHTCs) are valued for their extremely high melting temperatures and resistance to active oxidation. However, their low fracture strengths and the difficulties in shaping them into complex geometries hamper their widespread application. This study aims to fabricate zirconium diboride–silicon carbide (ZrB2‐SiC) composites reinforced with aligned SiC fibers by formulating suspensions containing a preceramic polymer, ZrB2, and SiC fibers. This study assessed the influence of fiber alignment on electrical and thermal conductivities, as well as on mechanical strength. The results revealed a significant enhancement in thermal conductivity, particularly when the fibers were aligned, effectively doubling it compared with the non‐aligned parts. Additionally, increasing the fiber content significantly improved the fracture strength, with composites containing 22.5 vol% fibers reaching fracture strengths over 57 MPa. However, the final values did not meet the theoretical expectations because the porosity in pyrolyzed parts exceeded 10%. Furthermore, the study demonstrated a 10‐fold increase in electrical conductivity with fiber alignment compared to that for non‐aligned composites. These results highlight the capability of paste extrusion‐based additive manufacturing in tailoring ultra–high‐temperature ceramic matrix composites (UHTCMCs) with aligned fibers, realizing their suitability for aerospace applications.

Development of ultra-high temperature ceramic matrix composites for hypersonic applications via reactive melt infiltration and mechanical testing under high temperature

AbstractIn the ongoing development of hypersonic technologies, material advancements play a key role in meeting the ever-increasing thermomechanical demands of these applications. Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) offer a promising solution for components operating under such extreme conditions. Their outstanding thermomechanical properties, including high temperature and thermal shock resistance, excellent thermal conductivity and mechanical strength, position them as ideal candidates for applications in fields like leading edges or inlet ramps for ramjets and scramjets. Due to their remarkable material composition, UHTCMCs are capable of operating in temperature regimes that surpass 1700 °C during their operation times under oxidizing atmospheres. At the German Aerospace Center (DLR), a UHTCMC material based on carbon fibres and a zirconium diboride matrix is being developed utilizing Reactive Melt Infiltration (RMI). With RMI, the orientation of the reinforcement fibres can be tailored, to enable the material to fulfill the demanding load requirements. The reactive melt infiltration process comprises three stages: preform fabrication, pyrolysis, and the actual melt infiltration. The foundation for important material properties of the final ceramic, including the matrix composition, is established in the preform production, which is a crucial step in the process. A boron- and zirconium diboride-based slurry is infiltrated into pitch-based carbon fibre fabric. Subsequently, the preforms are consolidated, pyrolysed, and infiltrated with molten Zr2Cu to obtain the UHTC matrix by in situ reaction with the preform elements. Scanning Electron Microscopy (SEM) and Energy-dispersive X-Ray Spectroscopy (EDX) enable the examination of the microstructural features, including the arrangement and distribution of zirconium diboride within the matrix. Mechanical evaluation of the UHTCMCs is conducted via 3-point bending tests at both room temperature and at elevated temperature at 900 °C. It has been demonstrated that Ultra-High Temperature Ceramic Matrix Composites can be produced by means of reactive melt infiltration, and that they retain their strength even at elevated temperatures.

Effect of increased intra-bundle spacing on mechanical behaviour of Cf- ZrB2–SiC ultra-high temperature ceramic matrix composites produced by slurry infiltration and hot pressing

A study has been carried out to examine the influence of augmented intra-bundle spacing achieved through innovative pre-treatment (heat treatment or ultrasonication) of carbon fibre (Cf) fabric, on mechanical properties of Cf-ZrB2-SiC composites processed by ZrB2–SiC slurry infiltration and hot pressing. Significantly enhanced Cf fabric intra-bundle spacing has facilitated homogeneous slurry infiltration, but has lowered elastic modulus, flexural strength, and fracture toughness compared to the composite with as-received Cf, because of fibre disorientation introduced during pre-treatment and its partial degradation by formation of interfacial ZrC during sintering. Notably, the composite with heat-treated Cf has shown superior fracture toughness (7.78 ± 0.4 MPa√m) and work of fracture (3043.25 ± 24.2 J/m2) compared to that containing ultra-sonicated Cf by 52.5 % and 95.7 %, respectively. Despite these variations, all the composites have exhibited non-catastrophic fracture behaviour during testing owing to the role of fibre pull-out, crack bridging, and crack deflection operating as toughening mechanisms.

Processing and performance of ultra high temperature ceramic matrix composite (UHTCMCs) using radio frequency assisted chemical vapour infiltration (RF-CVI)

Ultra-high temperature ceramic matrix composites (UHTCMCs) have been produced using a radio frequency assisted chemical vapour infiltration (RF-CVI) process. The composites were based on 2.5D carbon fibre preforms with a 0 / 90° (out of plane) fibre orientation and containing 23 % fibre volume fraction. These were initially impregnated with zirconium diboride (ZrB2) powder in the form of a slurry and then, after solvent removal, the majority of the porosity filled with pyrolytic carbon (PyC) using the RF-CVI process at 1273 K and 0.5 kPa chamber pressure. The latter resulted in a uniform rough laminar texture with good interfacial bonding. As intended, an inverse temperature profile was achieved using the RF heating, enabling uniform densification of the preform from the inside out, with no entrapped porosity and achieving 90 % of theoretical density in only 24 h, at least a tenfold reduction in processing time compared to the conventional CVI process and a fivefold reduction compared to other modified CVI processes such as forced flow or pressure gradient CVI. The resulting UHTCMCs displayed good mechanical strength and thermo-ablative behaviour.

Phase stability of W-containing high-entropy carbide with silicon addition at high temperatures

Reactive melt infiltration (RMI) is a typical method to produce carbon fiber-reinforced ultra-high temperature ceramic matrix composites (Cf/UHTCs), for which the molten Si is a very general and practical infiltrator. High-entropy carbide (HE-carbide) is a newly developed promising matrix phase of Cf/UHTCs. Understanding the phase equilibrium relation in the HE-carbide and Si reaction system can provide accurate guidance on designing the RMI process for preparing HE-carbide matrix composites with controlled phases and microstructure. This study systematically investigates W-containing HE-carbide and Si addition reactions at high temperatures. Samples with nominal starting compositions of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C-xSi (HEC-xSi, x = 2.5, 5 and 10 wt%) are prepared by spark plasma sintering technique at 1500 °C and 1700 °C with an axial pressure of 40 MPa for 10 min. The results show that adding 2.5 wt% or 5 wt% Si removes carbon from the HEC matrix, forming SiC and stable equimolar (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x phase with carbon deficiency at high temperatures. In contrast, besides the SiC phase, the addition of 10 wt% Si in the HEC matrix may form unstable transient phases of (Ti0.2Zr0.2Hf0.2Ta0.2W0.2)C1-x with supersaturated carbon deficiencies at high temperatures, which finally decomposes into non-equimolar HE-carbide (Ti0.2Zr0.2Hf0.2Ta0.2W0.2-y)C1-z and metal silicide WSi2 phases. The effects of the HEC and Si reactions on the microstructure evolution of the samples during sintering are discussed. Meanwhile, the mechanical properties of the samples with the reaction resulting microstructure are measured and briefly discussed.

Analysis and regularity of ablation resistance performance of ultra-high temperature ceramic matrix composites using data-driven strategy

High costs and time consuming associated with experimental trial-and-error result in low efficiency, creating an urgent need for a more effective strategy for ultra-high temperature ceramic matrix composites (UHTCMCs) development. Inspired by the exceptional performance of machine learning (ML) algorithms across various domains, this work employs ML algorithms to construct models and conduct in-depth analysis of the key factors and their patterns influencing the ablation resistance of UHTCMCs. A set of 26 dimensional features that could potentially impact the ablation resistance of UHTCMCs were established based on domain knowledge. Eight typical ML models were used to build and predict the linear ablation rate (LAR) of UHTCMCs. Results show that the random forest model has optimal generalization performance, with mean absolute error (MAE), mean squared error (MSE), and coefficient of determination (R2) being 2.75 μm s−1 and 7.3 (μm s−1)2, and 0.71 respectively. The Shapley additive explanations values based on the random forest model reveal that the key features affecting the LAR of UHTCMCs are ranked as average melting point of ceramics (AMPC) > thermal conductivity of material (TCM) > thermal expansion coefficient of oxides (TECO) > fabrication temperature of material (FTM), all showing a negative influence on the LAR. Symbolic regression further indicates that AMPC, TCM, and TECO have an exponential negative correlation with LAR. These data-driven conclusions have been thoroughly validated through the use of Cf/(TiZrHfNbTa)C composites. The established model can accelerate the discovery of material knowledge and provide reliable guidance for UHTCMC development.

Review on preparation technology of carbide resistant ultra-high temperature ceramic fiber

The rapid development of hyper-sonic vehicles has put forward an urgent demand for ultra-high temperature resistance ceramic fibers ceramic matrix composites. The properties of ultrahigh-temperature ceramic matrix composites made of carbon-based ultra-high temperature resistance ceramic fibers are excellent. Therefore, the preparation processes of several commonly used carbide-resistant ultrahigh-temperature ceramic fibers are described in detail. This review compares the advantages and disadvantages of five common methods (Molten-salt synthesis method, Chemical Vapor Reaction Method, Chemical Vapor Deposited method, Sol-Gel Method & Polymer-Derived method) for preparing ceramic fibers, summarizes the preparation methods that should be used in the face of different preparation requirements, and evaluates the improvement and prospect of each method. Among them, the polymer-derived method, as the most difficult and effective preparation method, has been given great hope by material scientists.

A universal strategy towards the fabrication of ultra-high temperature ceramic matrix composites with outstanding mechanical properties and ablation resistance

Materials with both excellent mechanical properties and good ablation resistance are urgently needed for the applications of thermal protection system in extreme high temperature oxidizing environments. However, owing to the lack of efficient fabrication processes, the existing materials suffer from either insufficient mechanical properties or poor ablation resistance. Herein, we report a novel solid–liquid combination fabrication strategy that successfully achieves the efficient incorporation of ultra-high temperature ceramics into 3D continuous carbon fiber performs as well as rapid densification. The relative density of the green body approaches the cubic close packing of spherical particles. Using Cf/ZrB2–SiC as an example, the as-prepared composite exhibits outstanding mechanical properties with a flexural strength surpasses 600 MPa and an unprecedented work of fracture of 11,851 ± 838 J/m2, which is two orders of magnitude higher than that of the currently reported monolithic ultra-high temperature ceramics. Moreover, the high ZrB2 content endows the composites with excellent ablation resistance and is thus capable of maintaining long-term non-ablative conditions at 2500 °C. The strategy possesses remarkable universality and high design flexibility, providing a time-saving and cost-effective universal strategy for the on-demand design and fabrication of high-performance ceramic, carbon, metal, and polymer matrix composites.

Local indentation response of carbon fibers embedded in a harsh environment: The sintered ultra-high temperature ceramic matrix

Understanding the properties of the constituent elements within Ceramic Matrix Composites (CMCs) is of paramount importance. During manufacturing process, the properties of the starting phases can undergo changes or be influenced by their interactions. In this work, micro-indentation analysis was used to selectively characterize matrix and fiber of Ultra-High-Temperature CMCs (UHTCMCs) produced by slurry infiltration of unidirectional pitch-derived carbon fabrics and sintering. A loading pre-factor was exploited to differentiate between indentations made on the matrix and those made on the fibers. The ZrB2-based matrix showed typical elasto-plastic behavior, leaving a residual imprint, with hardness and a modulus of 11.5 GPa and 220 GPa, respectively, consistent with its porosity, cracks and fiber content. Conversely, the fiber displayed no residual imprint and displayed hardness and modulus values of 1.1 GPa and 40 GPa, respectively. These values were attributed to the graphitic sheets buckling and residual thermal stress. Furthermore, the indentations indicated a transition zone between the matrix and fiber affecting mechanical behavior.

3D microstructure characterization of 2D Cf-ZrB2-SiC ultra-high temperature ceramic matrix composites using X-ray microscopy

A study has been carried out to examine the impact of fibre architecture on the infiltration permeability, constituent phase volume fractions, and matrix porosity of the carbon fibre (Cf)-ZrB2-20 vol% SiC ceramic matrix composites prepared through slurry infiltration, followed by hand lay-up and hot pressing. Unidirectional (UD) Cf-fibres in 0/0° and 0/90° orientations, as well as 8H satin woven Cf-fibres, have been utilized as reinforcement in the composites, which were subsequently densified through hot pressing after infiltration. Revelation of the 3D internal structure of the composites by X-ray microscopy has facilitated a thorough qualitative and quantitative evaluation of infiltration. The fraction of matrix (ZrB2 - 20 vol% SiC) present along three orthogonal axes (X, Y and Z) of the scanned composite blocks has been calculated, with Z representing the direction of infiltration. This study has revealed that the composites processed from UD Cf-fibre preform exhibits greater infiltration, because of higher intra-bundle infiltration compared to the 8H woven Cf-fibre, and the accompanying analysis provides insight into the formation mechanisms of matrix porosities.

Engineering Cf /ZrB2 -SiC-Y2 O3 for Thermal Structures of Hypersonic Vehicles with Excellent Long-Term Ultrahigh Temperature Ablation Resistance.

Ultrahigh temperature ceramic matrix composites (UHTCMCs) are critical for the development of high Mach reusable hypersonic vehicles. Although various materials are utilized as the thermal components of hypersonic vehicles, it is still challenging to meet the ultrahigh temperature ablation-resistant and reusability. Herein, the Y2 O3 reinforced Cf /ZrB2 -SiC composites are designed, which demonstrates near-zero damage under long-term ablation at temperatures up to 2500 °C for ten cycles. Notably, the linear ablation rate of the composites (0.33 µms-1 ) is over 24 times better than that of the conventional Cf /C-ZrC at 2500 °C (8.0 µms-1 ). Moreover, the long-term multi-cycle ablation mechanisms of the composites are investigated with the assistance of DFT calculations. Especially, the size effect and the content of the Zr-based crystals in the oxide layer fundamentally affect the stability of the oxide layer and the ablation properties. The ideal component and structure of the oxide layer for multi-cycle ablation condition are put forward, which can be obtained by controlling the Y2 O3 /ZrB2 mole ratio and establishing Y-Si-O - t-Zr0.9 Y0.1 O1.95 core-shell nano structure. This work proposes a new strategy for improving the long-term multi-cycle ablation resistance of UHTCMCs.

From outer space to inside the body: Ultra-high temperature ceramic matrix composites for biomedical applications

Ultra-high temperature ceramic matrix composites (UHTCMCs) are a new class of carbon fiber-reinforced non-brittle ceramics possessing a unique combination of properties (e.g. high fracture toughness, damage tolerance and corrosion resistance), originally developed for use in extreme hot and harsh environments, such as those found in aerospace and industrial applications. Interconnections between very remote fields more and more frequently come across to discover new solutions. In this study, we investigated the compression strength and cytotoxicity of UHTCMCs designed as biomaterials for future applications inside the body. Indeed, despite the advancements in the designing, manufacturing and surface modification, current prostheses are made of metals or alloys with well-known disadvantages. Near-fully dense Cf/ZrB2-SiC composites were manufactured through slurry impregnation followed by spark plasma sintering. A preliminary biological in vitro study demonstrated materials’ lack of cytotoxicity, making them promising candidates for further investigation for biomedical purposes.

Elevated temperature tensile and bending strength of ultra-high temperature ceramic matrix composites obtained by different processes

Elevated temperature tensile and bending strength of ultra-high temperature ceramic matrix composites obtained by different processes

Review of Research Progress in Nontraditional Machining of Ultrahigh-Temperature Ceramic Matrix Composites

Ultrahigh-temperature ceramic matrix composites are currently among the most promising high-temperature-resistant materials, owing to their high-temperature strength, high-toughness and excellent corrosion resistance; they are widely used in national defense and aerospace fields. However, it is a difficult material to machine, and high precision is difficult to achieve using traditional machining methods. Nontraditional machining methods are not constrained by material physical and mechanical properties, and good surface quality is easily obtained, which is an important direction in the field of ultrahigh-temperature ceramic matrix composites. This paper summarizes the recent nontraditional machining methods utilized in the fabrication of ultrahigh-temperature ceramic matrix composites. Firstly, various nontraditional machining methods for ultrahigh-temperature ceramic matrix composites based on borides, carbides and nitrides are reviewed, and the machining performances under different machining conditions are compared. Subsequently, the problems and challenges of ultrahigh-temperature ceramic matrix composite nontraditional machining are summarized and discussed. Lastly, the future development path of nontraditional machining methods for ultrahigh-temperature ceramic matrix composites is summarized and predicted.

Modification of SiBCN by Zr atom and its effect on ablative resistance of Cf/SiBCN(Zr) composites

The SiBCN(Zr) ceramics were synthesized via a polymer-derived ceramics route. Using this precursor, the precursor impregnation pyrolysis process prepared the Cf/SiBCNZr composites with low density (1.89 g/cm3). Compared to Cf/SiBCN, the Cf/SiBCNZr composites exhibit reliable thermal stability and ablation resistance in a wide temperature range. A dense oxide layer dominated by ZrO2 and SiO2 formed in situ on the surface of Cf/SiBCNZr, effectively preventing outside oxygen and further ablation. The introduced Zr is evenly distributed in SiBCN ceramics, which enables it to give full play to the ablation resistance of Zr at higher oxygen acetylene torch temperatures. This work enriches the fundamental understanding and offers engineering guidance for lightweight ultra-high temperature ceramic matrix composites.

Processing and characterization of ultra-high temperature ceramic matrix composites via water based slurry impregnation and polymer infiltration and pyrolysis

Uncoated PAN-based carbon fibre-reinforced ultra-high temperature ceramic matrix composites via aqueous ZrB 2 powder-based slurry impregnation coupled with mild polymer infiltration and pyrolysis, using allylhydrido polycarbosilane as source of amorphous SiC(O), were manufactured. To demonstrate the versatility of the process to realize tailored materials, unidirectional (UD), two dimensional (2D) and needle-punched (2.5D) cloths were impregnated. Microstructure and mechanical properties were investigated and correlated with fibre properties and architecture. The flexural strength was found over 250 MPa for unidirectional reinforced material, while the modulus exceeded 250 GPa for needle-punched one. The homogeneous distribution of UHTC phase around each single fibre and the weak fibre/matrix interface, due to the mild pyrolysis conditions, are the hallmark of this process and the key to improve durability and performance of materials for extreme environments without the application of expensive coating on fibres.

Recent advances in synthesis of ultra-high temperature ceramic matrix composites

A ceramic material designed for ultra-high temperatures (UHTCs) generally comprised of nitrides, carbides, and borides derived from transition metal elements, with a particular focuson compounds belonging to TaC and Group IVB (Hf and Zr). Hypersonic vehicle nozzles andengine components can take advantage of the unique characteristics of these materials. A broadrange of coatings and composites based on UHTC is currently being developed to conquer theinherent fragility, weak thermal shock resistance, and brittleness of bulk ceramics. Ultra-hightemperature materials with high entropy have gained considerable attention in recent years. Areview of the current state of the art of UHTC composites and coatings will be provided in thisreport. Properties and processing approaches to achieve the microstructure will be discussedfurther.

Experimental characterization of fatigue life of ZrB2-SiC based ultra high-temperature ceramic matrix composites

The development process of new Ultra High-Temperature Ceramic Matrix Composites (UHTCMC) for use in severe environments typical of space applications, such as thermal protection or rocket components, still lacks useful data for what concerns the properties influencing the structural behavior under the different load conditions. In particular, the fatigue life of the material plays a fundamental role in the design of full systems determining their resistance to typical vibrational loads. However, this property has been rarely investigated for UHTCMCs and its experimental characterization presents uncertainties related to the material specific behavior, which does not allow the application of traditional methodology employed for isotropic materials. In the present work, two different methodologies are proposed and applied to new ZrB2-SiC-based UHTCMCs, with either short or long continuous fibers, yielding in combination with numerical analyses to the determination of the σ/N curve for the two classes of materials.

Synthesis, microstructure and mechanical properties of lamellar YB2C2 – based ultra-high temperature ceramic composites

A significant improvement of the mechanical performance was observed following the introduction of rare earth oxides in ZrB2-based ultra-high temperature ceramic matrix composites (UHTCMCs), resulting in the formation of ternary boro-carbides of general formula REB2C2, belonging to a new class of layered compounds akin to MAX phases. These layered phases possess high melting points and could be responsible for the toughening of UHTCMCs, but their formation, properties and role were never fully investigated. In this study we focused on the potential routes for the synthesis of YB2C2 phases at temperatures typical of UHTC sintering, starting from Y2O3, carbon and four different boron sources (B, B2O3, BN, B4C) and their microstructure was analysed by SEM, XRD and TEM. The mixture with B4C led to the highest selectivity towards the formation of YB2C2 and was selected to fabricate a long carbon fibre reinforced YB2C2 ceramic composite, which was mechanically tested displaying a flexural strength of 380 MPa. Finally, the chemical stability in air of these materials was assessed.

Novel ceramic fibre - Zirconium diboride composites for solar receivers in concentrating solar power systems

Ultra-high temperature ceramic matrix composites (UHTCMCs) are a new class of composites which combine boride phases with carbon fibres to achieve new structural and functional properties and were originally designed for aerospace applications. For the first time, this work investigates the optical response of UHTCMCs in view of their possible application as high temperature solar absorbers in Concentrating Solar Power systems. Carbon fibre-reinforced ZrB2 pellets with different fibre type and arrangement were manufactured and characterized from the point of view of optical properties and surface microstructure. The composites had high fractions of ZrB2 (∼40 vol%) and carbon fibres (up to 60 vol%). Spectral hemispherical reflectance in the range 0.3–16 μm wavelength was assessed and compared to pure boride and graphite phases. Irrespective of the fibre architecture, the solar absorptance significantly increased with respect to the pure boride, reaching or even overpassing the solar absorptance of silicon carbide. Thermal emittance, calculated from 800 K to 1500 K temperature, increased as well in comparison to the pure boride, but always remained lower than that of SiC. These optical properties, combined with structural damage tolerance and light weight, suggest that UHTCMCs are of great interest as high temperature solar absorbers, overpassing the weaknesses of current solar receivers, as well as those of the most promising alternative materials to date.