Search Results (114)

This paper presents a miniaturized ultra-wideband high-pass filter integrated with a notch function based on low-temperature co-fired ceramic (LTCC). The design motivation is to realize continuous wideband high-pass transmission while rejecting a narrow in-band interference/leakage component in compact RF front-end modules. The proposed design employs a cascaded structure of a seventh-order quasi-elliptic HPF and a three-section $\lambda /4$ stub notch filter in a single multilayer LTCC chip. Multiple transmission zeros (TZs) are introduced to improve the lower-stopband selectivity, while the three-section coupled-line NF produces a tunable localized rejection band. The LTCC implementation further integrates multilayer capacitors, three-dimensional helical inductors, shielded strip-line coupling stubs, a grounding compensation capacitor, and an isolation wall to balance compactness, impedance matching, and parasitic suppression. The fabricated chip achieves an ultra-wide bandwidth of 2.35 octaves, a notch 20 dB FBW of 8.5%, an insertion loss below 2 dB, a 60 dB roll-off rate of 154.1 dB/GHz within the lower stopband, and a voltage standing wave ratio (VSWR) less than 2. Experimental results validate that the proposed compact chip meets communication requirements and is suitable for 5G base stations, radar systems, and other applications. The chip dimensions are 4.5 mm × 3.2 mm × 2.5 mm. Full article

High-entropy transition-metal diborides represent a promising class of ultra-high temperature ceramics. However, atomic insights into their high-temperature elastic response, anisotropic deformation, and fracture mechanisms remain elusive. Herein, we perform molecular dynamic simulations to study the thermomechanical behaviors of (Hf_0.2Zr_0.2Ta_0.2Ti_0.2Nb_0.2)B₂ from 900 to 3300 K by developing an ab initio accuracy deep-learning potential. The proposed potential accurately reproduces lattice parameters, equations of state, and elastic constants, in excellent agreement with density functional theory calculations and available experiments, and remains transferable under thermally expanded and compressed states. The simulations reveal anisotropic thermal expansion, with the out-of-plane expansion exceeding the in-plane expansion, together with progressive elastic softening while preserving C₁₁ > C₃₃ due to the dominant in-plane B-B bonding network. Furthermore, strain-rate- and temperature-dependent tensile and compressive responses show marked crystallographic anisotropy, tension–compression asymmetry, and severe thermomechanical degradation. Atomic structural evolution demonstrates that tensile fracture is dominated by bond stretching and progressive damage accumulation, whereas compressive failure is attributed to densification- and shear-mediated structural instability. These findings provide an atomistic understanding of the thermomechanical behavior and fracture mechanisms of the prototypical single-phase (Hf_0.2Zr_0.2Ta_0.2Ti_0.2Nb_0.2)B₂ high-entropy diboride, offering valuable insights into the design of ultra-high temperature ceramics under extreme service environments. Full article

Ultra-high-temperature materials (UHMs) are indispensable for extreme thermal environments (e.g., temperatures exceeding 2000 °C); however, their practical implementation remains severely constrained by demanding processing conditions, including extreme sintering temperatures, prolonged cycles, densification barriers and high equipment cost. In order to meet the low-cost and ablation-resistant requirements of aircraft nose cones, a facile organic–inorganic hybrid strategy is proposed to fabricate ZrB₂–HfC–SiC composites using a high-char-yield 1,2-dicyanobenzene (DCB) binder, enabling low-temperature moulding at merely 250 °C (2 h; 20 MPa). Upon high-temperature oxidative exposure, the DCB matrix undergoes in situ pyrolysis and synergistic co-sintering with the ceramic powders, producing a multi-layered, self-protective structural architecture. A comprehensive structure–temperature map correlating temperature-dependent phase evolution with flexural strength and thermal conductivity is established, thereby elucidating the underlying self-healing and ablation-resistance mechanisms. The hybrid material in this work exhibits excellent flexural strength, ablation resistance and thermal stability. This study successfully reconciles the long-standing contradiction between low-temperature processability and ultra-high-temperature (2600 °C) service durability, offering a scalable route for next-generation thermal protection systems. Full article

Ultra-high-temperature ceramics (UHTCs), including transition-metal carbides, nitrides, and diborides, have emerged as a class of promising structural materials for applications in extreme aerospace and energy environments. Their strong covalent–metallic bonding endows them with exceptionally high melting points, elastic moduli, and thermal stability. Nevertheless, intrinsic brittleness, limited oxidation resistance, and poor sinterability remain key challenges for the engineering application of conventional UHTCs. Recently, novel material design strategies such as multiphase composites, microstructural engineering, and compositional complexity have emerged. Among these, high-entropy UHTCs (HE-UHTCs) have attracted significant attention due to their configurational entropy, lattice distortion, and sluggish diffusion effects, which collectively enhance oxidation resistance, thermal stability, sinterability, and mechanical performance. This review summarizes the crystal chemistry, mechanical behavior, oxidation, and ablation properties of conventional UHTCs and HE-UHTCs. The four core effects of HE-UHTCs—configurational entropy, lattice distortion, sluggish diffusion, and cocktail effects—are discussed in relation to their mechanical properties and oxidation resistance. The roles of computational materials science, including density functional theory (DFT), molecular dynamics (MD), and machine learning, in composition screening and property prediction are critically reviewed. Finally, key challenges and future directions for the rational design and engineering application of UHTCs are discussed. Full article

Zirconium carbide (ZrC) is a leading candidate for advanced nuclear reactor components due to its ultra-high melting point, thermomechanical stability, and low neutron absorption. However, its irradiation damage behavior and mechanism remains underexplored. In this work, dense pressureless-sintered ZrC ceramics with low-neutron-absorption MoSi₂ additives were irradiated with 500 keV He²⁺ ions at room temperature to peak damage levels of 0.30, 1.49, and 2.97 dpa. The changes in their microstructure, bonding states, and property were analyzed via TEM, GIXRD, Raman spectroscopy, nanoindentation, and TDTR. ZrC retained crystallinity regardless of high-density black-spot defects, while MoSi₂ exhibited severe amorphization and swelling. Lattice expansion and partial Zr-C bond breakage with C-C bond formation were confirmed, with maximum hardening at 1.49 dpa and significant elastic modulus reduction at 2.97 dpa. Thermal conductivity decreased modestly and showed minimal dose dependence, indicating a saturation effect. These results elucidate defect evolution in pressureless-sintered ZrC-MoSi₂ ceramics and support its application in high-irradiation nuclear environments. Full article

Hard ceramic coatings are essential for extending the performance of metal parts under the extreme heat and stress found in aerospace and defense environments. There is a major knowledge gap regarding this topic in the current literature. While there has been significant research on individual fabrication methods or specific coating materials separately, no previous review has combined experimental lifecycle data with a broad computational design approach that covers the entire design-to-deployment process. This review fills that gap by offering a unified roadmap from integrated computational materials engineering (ICME) to machine learning (ML). This roadmap speeds up the rational design of coatings for next-generation aerospace systems. The practical importance of this framework is its clear use in gas turbine engine qualification, hypersonic vehicle thermal protection, and landing gear surface engineering. It can cut down on experimental trial-and-error cycles by allowing ML-guided composition screening and condition-based maintenance through digital twin integration. The main ceramic material systems, tungsten carbide (WC), boron nitride (BN), boron carbide (B₄C), silicon carbide (SiC), alumina (Al₂O₃), and zirconia (ZrO₂), are examined for their protective roles in aerospace-grade alloys. A key contribution is the multiscale computational framework that includes density functional theory, molecular dynamics, finite element analysis, and ML-driven inverse design. Together, these methods improve predictions for thermal breakdown, multi-axial stress responses, and coating lifetime. Future research should focus on ultra-high-temperature ceramics, multifunctional self-healing coatings, and surface engineering methods driven by data. Full article

Ultra-high-temperature ceramics (UHTCs) in the Ta–Hf–C ternary system are of significant interest for extreme aerospace and energy applications due to their melting points near 4000 °C. However, their synthesis typically requires extreme temperatures and pressures. This study reports a pectin-assisted low-temperature route for Ta-rich Ta_xHf_1−xC powder synthesis via carbothermal reduction at 1500 °C. The effect of Ta/Hf molar ratios (2.7/1, 0.9/1, and 0.3/1) on phase evolution, crystallinity, and morphology was systematically investigated. FTIR confirmed the successful formation of homogeneous hybrid organic–inorganic precursors through the chelation of metal ions with pectin functional groups. XRD results demonstrated that the Ta-rich composition (Ta/Hf = 2.7/1) promotes the formation of a high-purity (95.87%) cubic solid solution (lattice parameter a = 4.453 Å) with sharp reflections and improved crystallinity. In contrast, Hf-rich samples exhibited incomplete conversion, leaving unreacted HfO₂ and Ta₂Hf₆O₁₇ oxide phases due to the high thermodynamic stability of hafnia. Microstructural analysis revealed quasi-spherical Ta_xHf_1−xC particles with an average size of approximately 123 nm, together with finer residual oxide particles of about 50 nm. Overall, these results demonstrate that pectin-assisted precursor chemistry is an effective strategy for promoting low-temperature carbide formation in Ta-rich Ta_xHf_1−xC compositions. Full article

HfC, TaC, and HfTaC composite coatings were successfully fabricated on SiC-coated carbon/carbon (C/C) composites using the double glow plasma alloying (DGPA) technique. The microstructure, mechanical properties, and tribological behaviors of the coatings were systematically investigated. The HfTaC coating exhibited a dense and uniform structure with good interfacial integrity and a compositionally graded transition layer, effectively relieving thermal stress. The hardness of HfTaC and HfC coatings (approximately 12 GPa) was higher than that of the TaC coating. Moreover, the higher K value (1.02) and H/E ratio (H/E = 0.09, H³/E² = 0.085 GPa) indicate that the HfTaC coating exhibits good load-bearing capacity and toughness. Under both 5 N and 15 N loads in the reciprocating friction, the HfTaC coating maintained the lowest and most stable friction coefficient (~0.18). Under the 15 N load, it exhibited the smallest specific wear rate. Observation of the wear scars revealed that the HfC and TaC coatings suffered from pore formation and flake-like spallation, while the HfTaC coating retained structural integrity with only minor cracks. In high-temperature ball-on-disc friction tests up to 500 °C, the wear mechanism of the HfTaC coating gradually transitioned from mild abrasive wear to severe oxidative and adhesive wear, yet the HfTaC coating still provided effective protection. These findings demonstrate that the DGPA-fabricated HfTaC coating is a promising candidate for enhancing the wear resistance and service durability of C/C composites. Full article

The demand for materials that can operate reliably in extreme environments, including rocket nozzles, re-entry heat shields, sharp leading edges, high-velocity impact, and high-temperature energy systems, continue to drive advances in thermal–structural materials. Carbon/Carbon composites remain a leading baseline because of their low density, high-temperature mechanical retention in inert atmospheres, and excellent thermal-shock tolerance. However, long-term durability is constrained by rapid oxidation in air at elevated temperatures, limited fracture toughness and elastic modulus in many architectures, and high manufacturing cost driven by multi-cycle densification and stringent quality assurance. Consequently, contemporary strategies increasingly rely on modifying Carbon/Carbon composites with ultra-high-temperature ceramics and adopting accelerated or simplified manufacturing routes. This review synthesizes recent progress in the design, manufacture, and application of high-performance modified Carbon/Carbon composite systems for extreme aerospace environments, emphasizing composition/architecture selection, oxidation, and ablation protection, toughening concepts, and cost-aware densification. Because extreme environments performance is governed by coupled aerothermal loading, gas–surface chemistry, internal transport, recession, and thermomechanical response, the review also consolidates the multiscale modeling and software toolchains increasingly used to size thermal-protection systems, interpret experiments, and guide down-selection. Key challenges and future directions are further discussed for reusable materials and validated performances beyond ~2000 °C. Full article

Geopolymer concretes are increasingly regarded as advanced construction materials for applications requiring high thermal and chemical resistance. This article is a continuation of previously published research and focuses on the mechanical behaviour of geopolymer concretes containing aggregates made of foamed geopolymers and lightweight mineral aggregates, such as expanded clay and perlite, intended for use in chimney flue components. The aim of the study was to determine the influence of lightweight aggregates on the relationship between thermal insulation and the strength parameters of geopolymer concretes intended for use at elevated temperatures. Foamed geopolymer aggregates were produced by a controlled chemical foaming process, followed by grinding to specific grain sizes, yielding highly porous aggregates with low thermal conductivity, reaching approximately 0.075–0.099 W/(m·K). These aggregates were used as lightweight fillers in geopolymer concretes based on class F fly ash activated with alkaline solutions. The resulting composites were designed to combine low density and high thermal insulation with adequate mechanical strength. The mechanical properties of the developed concretes were assessed on the basis of compressive strength tests on cubic specimens and tensile strength in beam bending tests, carried out in accordance with standards. The results presented confirm that the use of foamed geopolymer aggregates enables a simultaneous increase in thermal insulation and the design of ultra-lightweight structural elements with sufficient load-bearing capacity for chimney systems (including suspended ones). This combination of low thermal conductivity, reduced mass, and appropriate mechanical properties makes geopolymer concretes with lightweight mineral and geopolymer aggregates a promising alternative to traditional ceramic materials. Full article

A novel amorphous Hf-MOFs precursor was successfully synthesized and converted into HfC nanoparticles via one-step pyrolysis. The effects of metal/ligand molar ratios, solvent types, and pyrolysis temperature were systematically studied. High-purity spherical HfC nanoparticles (44.30 ± 9.63 nm) were obtained at 1500 °C using a 1.5:1 metal/ligand molar ratio with mixed anhydrous ethanol/deionized water solvents. At a pyrolysis temperature of 1700 °C, the as-synthesized HfC nanoparticles possessed an exceptionally low oxygen content of 0.76%, alongside a carbon content of 6.42% that almost perfectly matches the theoretical value of stoichiometric HfC. The formation mechanism involving Hf-O-C coordination and carbothermal reduction was clarified. Additive-free HfC ceramics were fabricated using the as-synthesized HfC nanoparticles via spark plasma sintering (1950 °C, 30 MPa, 20 min). The resulting ceramics exhibited a relative density of 96.7% and a Vickers hardness of 20.2 GPa, both of which are significantly superior to those of ceramics sintered from commercial HfC powders under identical conditions (95.8% and 17.8 GPa, respectively). This work provides a promising and feasible pathway for the preparation of other high-quality ultra-high temperature hafnium-based carbide powders and ceramics. Full article

Silicon carbide (SiC) ceramics are among the most attractive materials for lightweight armor because they combine low density (3.0–3.2 g/cm³), high hardness, and high thermal and chemical stability; however, their densification remains challenging because of strong covalent bonding and low self-diffusion. This review analyzes the main sintering routes used for armor-grade SiC ceramics, including solid-state sintering, liquid-phase sintering, hot pressing, gas-pressure sintering, hot-isostatic pressing, ultra-high-pressure sintering, two-step sintering, and spark plasma sintering, together with additive systems based on B, C, Al₂O₃, Y₂O₃, MgO, CaO, and rare-earth oxides. Reported data show that solid-state sintering typically requires 2100–2300 °C and yields 90–95% relative density, whereas hot pressing and liquid-phase sintering achieve 96–99% density at lower temperatures, generally with a flexural strength of 350–800 MPa, fracture toughness of 3.5–7.0 MPa·m^1/2, and hardness of 20–30 GPa. Among the reviewed methods, spark plasma sintering provides near-theoretical density (≥99%) together with the most favorable combination of strength (up to 850 MPa) and hardness (up to 35 GPa). Overall, liquid-phase sintering and spark plasma sintering offer the most favorable balance between densification, microstructural control, and armor-relevant mechanical performance. Full article

Ceramic materials are indispensable to aerospace and defence technologies, where structural and functional components are required to withstand extreme thermal, mechanical, and chemically aggressive environments. Traditionally valued for their exceptional thermal stability, oxidation resistance, and corrosion resistance, ceramics have nonetheless been constrained by their inherent brittleness, which has limited their widespread adoption in load-bearing structural applications. This review surveys the principal tough ceramic systems currently employed in aerospace and defence, including SiC, Al₂O₃, ZrO₂, Si₃N₄, SiC/SiC composites, and ultra-high-temperature ceramics (UHTCs) such as ZrB₂ and HfB₂. In parallel, it outlines advanced processing and manufacturing routes that enable enhanced microstructural control, improved reliability, and scalability for industrial deployment. Special attention is devoted to thermal and environmental barrier coatings (TBCs and EBCs), which provide critical protection against oxidation, corrosion, and severe thermal cycling in propulsion, power-generation, and hypersonic systems. Finally, the review highlights key material selection criteria for aerospace and defence platforms and discusses emerging trends that integrate tough ceramics with next-generation manufacturing technologies, underscoring their pivotal role in enabling high-performance, durable, and resilient systems for future extreme-environment applications. Full article

During high-speed flight, intense friction on the aircraft surface always occurs due to atmospheric fluid medium. The resultant high frictional drag will trigger a significant aerothermal effect, and thus raise the surface temperature sharply to 1000–3000 °C. This extreme heat not only remarkably reduces the aerodynamic efficiency but probably also causes thermal failure of the structural integrity and damage of internal components. Therefore, robust heat-resistant materials are the preferred choice for designing high-speed aircraft due to their benign tolerance to high temperature, oxidation and ablation as well as large strength and durability. This work systematically unveils the generation mechanism of frictional drag in high-speed flight and introduces the characteristics and applications of typical thermal insulation materials (TIMs). After that, the recent progress in a thermally protected material system including metal-based alloys and metal-doped compound materials, ultra-high-temperature ceramics (UHTCs), carbon (C)/carbon (C) and C/SiC composites, ceramic matrix composites (CMCs), UHTCs-modified C/C and C/SiC composites is conducted. Finally, the current technical bottlenecks are discussed, simultaneously proposing the development direction of novel TIMs for the potential applications for high-speed aircrafts. Full article

High-temperature particulate matter (PM) filtration remains a fundamental challenge, because most fiber filters not only face the challenge of high temperatures but also suffer from an inherent trade-off between capture efficiency, pressure drop, and service life. This paper reports a hierarchical layered zirconia (ZrO₂) ceramic fiber aerogel featuring a continuous multiscale gradient. The aerogel was prepared by gradient air-blown spinning, and the resulting structure has directional order, with the fiber diameter gradually decreasing from upstream to downstream, thus forming a pore size gradient and achieving hierarchical particle interception across multiple scales. This rational design simultaneously suppresses surface clogging and reduces flow resistance, resolving the longstanding trade-off between efficiency and permeability. Consequently, this aerogel achieves an ultra-high filtration efficiency of 99.96%, a low pressure drop of 156 Pa, and a high dust-holding capacity of 101 g m⁻². The material also exhibits outstanding mechanical toughness (80% compressive strain elasticity and 25.75% tensile fracture strain) and thermal stability up to 1000 °C. Moreover, it maintains over 99.95% filtration efficiency at high temperatures and can be fully regenerated through 800 °C heat treatment. This work establishes a structure-based design paradigm for high-temperature filtration media and provides a scalable pathway for next-generation industrial flue gas purification. Full article