High-temperature Composites Research Articles

Superior high-temperature strength of a carbide-reinforced high-entropy alloy with ultrafine eutectoid structure

Refractory alloys with high-temperature softening resistance are crucial for extreme high-temperature components in aerospace and weapon equipment. Traditional alloys and single-phase refractory high-entropy alloys suffer from unstable microstructures and loss of strength at high temperatures. Here we report a strategy to obtain a superior strong high-entropy alloy by introducing carbides to form micro-nano scale eutectic and eutectoid structures. These metal-carbide interfaces remain stable under high-temperature deformation and exhibit strong dislocation blocking effects. The ultrafine eutectoid structure provides a primary strengthening effect due to its numerous enhanced phase interfaces. The resulting alloy achieves a high temperature yield strength of 1.17 GPa at 1473 K and 0.92 GPa at 1673 K. This work provides valuable insights for optimizing the high-temperature performance and microstructure design of high-temperature composites to further extend their potential applications in high-temperature areas.

Methodology for optimizing the radio absorption capacity and mechanical strength of composite structural materials

The possibility of impregnating high-strength fabrics under pressure with a modified binder is considered. The development of high-temperature composites that have not only high strength, but also microwave absorption properties is inextricably linked with new products being developed and the imposition of more stringent tactical and technical requirements on them. For the successful introduction of these composites into the field of mechanical engineering, one of the necessary conditions is the assessment of their stress-strain state at the design stage. This method allows producing the fabric for aircraft details with high strength. The purpose of the study is to evaluate the absorption of microwave waves and study the physical and mechanical characteristics of composites obtained by vacuum infusion.

A MACHINE LEARNING-BASED ACCELERATED PYROLYSIS CHARACTERIZATION AND OPTIMIZATION OF HIGH-TEMPERATURE COMPOSITES

Manufacturing polymer-based composites for high-temperature applications involves a series of complex steps during which the material undergoes several transformations. These typically include a lay-up step, a curing process, a high-temperature pyrolytic process to convert the resin phase into amorphous carbon, followed by several resin backfill steps, and finally, graphitization to achieve the desired crystalline structure of carbon atoms. The parameters used during the pyrolysis process significantly affect the degradation reactions, the final yield, laminate permeability, and hence the final properties of the material. Typically, extensive testing is required to characterize pyrolysis kinetics and identify optimal processing conditions. This paper addresses these challenges through a novel probabilistic machine-learning (ML)-based approach for the accelerated characterization and optimization of the pyrolysis process, utilizing theory-based transformations of limited experimental data affected by noise and errors. Gaussian Process Regression (GPR), a Bayesian probabilistic approach to regression, is used to determine optimal test parameters to accurately characterize pyrolysis kinetics and achieve the desired yield while satisfying specific constraints. This approach can be used to improve the processing efficiency of high-temperature composites and increase their performance with minimal experimental effort.

Thermal shock effects on the microstructure and mechanical properties of iron-based composites reinforced by in-situ Fe2B/FeB ceramic phases

Recently, high-temperature composites reinforced with in-situ phases have been developed as a new class of composites for harsh environments. The behaviour of these composites under sudden heating and cooling conditions is greatly influenced by the type and fraction of components. The aim of this study is to investigate the microstructural properties and mechanical response of iron based composites after thermal shock cycling. The fabrication process involved in-situ powder metallurgy (IPM) sintering of Fe–B4C starting powders. The samples were subjected to thermal shock with a constant temperature differences (ΔT: 600 °C) and varied cycles (N: 1–50). Comparison of microstructural changes and mechanical behaviour before and after thermal shock has been carried out. The boron atoms released from the initial B4C generated diffusion zones in the matrix dominated by iron boride phases (Fe2B/FeB). An effective matrix-reinforcement interface has been created by in-situ powder metallurgy, where boride phases are almost homogeneously distributed in the iron matrix. While the hardness of the composites was significantly developed by the Fe2B/FeB phases, the addition of B4C resulted in a reduction in the coefficient of thermal expansion (CTE). The in-situ phases contributed in the minimisation of the coefficient mismatch by balancing the thermal expansion coefficients between iron and the initial B4C. Under the influence of thermal shock, microcracks and then macrocracks formed on the sample surfaces, increasing in width and depth with thermal cycles. This resulted in accelerated fracture damage under post-thermal loading. Both the impact and flexural strengths of the samples were significantly reduced as the number of thermal cycles increased. Although the 20% B4C reinforced composite provided maximum hardness, it showed poor resistance to thermal loading. The best results for mechanical loads were achieved by the 5% B4C reinforced composite, which showed no cracks even after 50 thermal cycling.

The Role of Carbon Fiber Composite Materials in Making Electric Aircraft a Reality

As the aerospace industry seeks sustainable alternatives to traditional aviation, electric aircraft have emerged as a promising solution to reduce carbon emissions and reliance on fossil fuels. Central to this transition is the development and integration of advanced materials that enhance the performance and efficiency of these next-generation aircraft. Compound materials possess various significant abilities, including the capability to withstand fatigue, resist corrosion, and manufacture lightweight components with minimal compromise to reliability, among others. Nanocomposites constitute a subset of materials within compounds, recognized for their superior mechanical properties compared to standard composite materials. The utilization of nanocomposites in the aerospace sector is presently encountering a research gap, primarily in identifying future application scopes. This paper reviews the critical role of carbon fiber composites and nanocomposites in electric aviation, highlighting their transformative impact on aircraft design, battery integration, and overall sustainability. By offering unparalleled strength-to-weight ratios, superior thermal management, and innovative structural possibilities, these materials significantly advance the capabilities of electric aircraft. Furthermore, it discusses the advancements in material technology, including high-temperature composites, hybrid composites, and nanocomposite materials, and addresses the challenges and future directions in composite application. The paper underscores the pivotal role of composite materials in achieving a greener, more efficient, and technologically advanced aerospace industry, marking a significant step towards sustainable air transportation.

Preparation of NiAl-AlMg6 Functionally Graded Composite Using the Energy of a Highly Exothermic Ti-C Mixture during Self-Propagating High-Temperature Synthesis.

A functionally graded composite NiAl-AlMg6 was prepared using the pressure of gaseous reaction products (impurity gases) produced during the synthesis of reactive powders in a sealed reactor. It has been shown that this method can be used to prepare a NiAl/AlMg6 composite with both chaotically oriented pores in the NiAl layer and unidirectionally oriented pores (lotus-type pores). The pore shape in NiAl was found to be dependent on the pressure of the impurity gases and hydrogen present in the starting titanium powder. A mechanism for pore formation in NiAl and AlMg6 composite during SHS is proposed. Thus, functionally graded high-temperature composites can be produced by SHS in a sealed reactor using the chemical reaction energy and the pressure of impurity gases and hydrogen. Additionally, minimizing the influence of impurity gases on the contact zone increases the interface area between NiAl and AlMg6.

Nano and micron WC particles reinforced Hastelloy C22 coatings manufactured by directed energy deposition

The performance of Hastelloy C22 matrix composite with different reinforced particles is strongly related to microstructural aspect of the coating. In this study, a novel approach for fabricating advanced and high wear resistant nickel-based high-temperature composites by directed energy deposition (DED) was investigated, which enhances the Hastelloy C22 matrix by blending nano and micron WC particles. The microstructure and phase composition of the WC/C22 composite coatings were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The main phases of WC/C22 composite coating are γ-Ni, M6C, WC, W2C and M12C, where M12C and M6C are distributed at grain boundaries to inhibit grain growth and play the role of fine grain strengthening. In performance testing, the nano/micron WC/C22 composite coating showed a 71.04% increase in microhardness, a 92.3% reduction in mass loss, and significantly improved electrochemical corrosion performance compared to the C22 coating.

Characterization of inclusions inhibiting high thermomiotic behavior of Y2W3O12

The present study delves into the significant impact of secondary phases created during the formation process of Y2W3O12. Thermomiotic ceramic materials exhibit negative thermal expansion (NTE). Among those ceramics, Y2W3O12 is distinct for having phase stability over a high-temperature range as well as high volumetric NTE. These properties make Y2W3O12 an unprecedented additive for thermal expansion coefficient (CTE) engineering for high-temperature composites. Synthesis of this material is continuously concluded with a higher thermal expansion than the theoretical. To fully take advantage of this material's unique properties, the origin of the mismatched NTE should be fully understood. In this study, the popular solid-state synthesis approach of Y2W3O12 across all synthesis steps was examined in detail. Each secondary Y-W-O phase's contribution to the CTE was calculated, and the final value closely aligns with the measured NTE within 3.7 %, demonstrating the impact of secondary phases on the material's thermal behavior.

A peridynamic model for coupled thermo-mechanical-oxygenic analysis of C/C composites with SiC coating

The oxidation induced by coating cracking is a general failure mode of high-temperature composites such as C/C and C/SiC. However, this failure mode has not been fully investigated due to the lack of a method suitable for both crack simulation and oxidation interface capture. In this paper, a coupled thermo-mechanical-oxygenic peridynamic model is proposed for SiC-coated C/C composites in an oxidizing environment. The ordinary state-based peridynamics is extended to plane strain thermoelastic problems for orthotropic media to calculate the crack distribution. Cracks in the coating are modeled as oxygen diffusion channels and the peridynamic oxidation equation is developed to simulate the oxidation of the C/C substrate. Furthermore, the peridynamic non-Fourier heat transfer equation is employed to consider the finite thermal propagation speed and the model is validated by experimental results. Numerical examples are presented to investigate the oxidation failure after thermal shock, non-Fourier thermal shock fracture, and stress oxidation failure of SiC-coated C/C composites.

Review of Technological Advances in High Temperature Overhead Line Composite Conductors

ACSR (Aluminium Conductor Steel Reinforced) conductors consisting of pure aluminum wires helically stranded around a core of high strength galvanized steel core wires are widely used in overhead transmission line applications. While the steel wires provides the required strength, the outer aluminium serves as electricity conducting member. The thermal rating or ampacity of conductors is the maximum current that a circuit can carry within the temperature limits as dictated by the allowable conductor sag or by the annealing onset temperature of the conductor, whichever is lower. On a continuous basis, ACSR may be operated at temperatures up to 100°C without any significant change in the conductor’s physical properties. Above 100°C, aluminum wires loses tensile strength over time and becomes "fully annealed" giving rise to increased thermal expansion of the conductor; this causes excessive sagging reducing the clearance between the ground and the energized conductors.
 While, the electric utilities are posed with increased challenges of production of additional capacities and building new transmission circuits to meet the ever growing demand and the high cost and environmental restrictions of constructing new lines, methods are being explored to increase their capacity with minimum changes in the existing towers. Replacement of the existing conductor with a advanced high temperature composite (HTC) conductors operating upto temperatures of 200°C with reduced sagging characteristics have been attempted and an increase in capacity of 30-80%, can be achieved through application of these composite conductors.
 The advanced HTC conductors with varied combinations of core material and outer conducting wires are being tried so as to achieve wide ranging properties. In general, HTC conductors features the combinations of either soft aluminum wires with ultra high strength steel or temperature resistant aluminium with or fiber reinforced metal/polymer matrix composites as the core. Both the alumina fiber reinforced temperature resistant aluminium metal matrix composite and the carbon fiber reinforced high temperature polymer resin composite wires as the core material appears to have favorable applications. The comparative performance of the HTC depends on the degree to which both outer aluminum strand and reinforcing core’s physical properties are stable at high temperature and on the elastic, plastic, and thermal elongation of the combined HTC.
 The summary of various developments realized in the area of composite conductors and their relative merits and demerits have been discussed in detail.

Synthesis and Characterization of Pyrimidine‐Based Novel Phthalonitrile Resins with Excellent Processing Performance and High Glass Transition Temperature

AbstractThree phthalonitrile monomers containing pyrimidine ring and benzene ring side group were successfully synthesized with 4, 6‐dichloro‐2‐phenylpyrimidine, three kinds of phenols (resorcinol, bisphenol A and bisphenol AF) and 4‐nitrophthalonitrile via nucleophilic substitution reaction. All the phthalonitrile monomers exhibited excellent processing performance due to low melting points (Tm) (below 100 °C) and wide processing windows (difference between melting temperature and curing temperature) above 140 °C. By introducing pyrimidine ring and benzene ring side group, the lower melting point of monomers did not affect the thermal stability and thermal mechanical properties of the phthalonitrile resins based on different bisphenols. In particular, 5 % thermal decomposition temperature (T5%) and glass transition temperature (Tg) of phthalonitrile resin based on resorcinol surpassed 455 and 400 °C while storage modulus (E′) was 3209 MPa. Therefore, phthalonitrile resin containing pyrimidine ring and benzene ring side group have potential applications in the field of high temperature resistant polymers and composites.

Extreme Thermal Stability and Dissociation Mechanisms of Purified Boron Nitride Nanotubes: Implications for High-Temperature Nanocomposites

A fundamental understanding of the thermal behavior of reinforcement materials is crucial to fully exploit their properties in composites. Boron nitride nanotubes (BNNTs), structural analogues to carbon nanotubes, are a strong candidate for nanofillers in high-temperature composites due to their high thermal stability, oxidation resistance, excellent mechanical properties, and high thermal conductivity. In this paper, samples of high-quality, high-purity BNNTs were tested to thermal failure in an inert atmosphere for the first time up to 2500 °C. A significant fraction of the BNNTs survived temperatures as high as 2200°, and the BNNT samples were completely undamaged at temperatures as high as 1800 °C. Boron nitride (BN) nanopowders were tested identically to perform a comparative study, as hexagonal BN is commonly found in purified BNNT samples. Observed color darkening, significant weight loss, an increased boron atomic level, significant weight gain upon oxidation, the presence of boron oxide compounds in an oxidized sample, and the observed boron clusters at the nanoscale indicate dissociation of B-N bonds in the BNNT sample at 2200 °C. The stability of BNNT structures was observed up to 2000 °C, with local/partial wall dissociation or unzipping, and complete survivability of highly crystalline BNNTs is demonstrated up to 1800 °C. This paper presents the first-ever study on extreme temperature thermal stability of purified BNNTs in an inert atmosphere analogous to manufacturing processes for high-temperature nanocomposites.

Future insights on high temperature ceramics and composites for extreme environments

AbstractThis document summarizes key research directions as they emerged during the proceedings of the Inaugural Orton Workshop that aimed to define scientific areas of current interest to the ceramics community around the theme of: “High Temperature Ceramics and Composites for Extreme Environments.” The topic was selected due to the timely interest in such materials to meet the needs of hypersonic aviation and space exploration and habitation. Experts from funding agencies supporting ceramics research, thought‐leaders from academia with expertise spanning materials processing, characterization, and modeling, as well as research and development leaders from key (aviation‐related) industries, gathered to evaluate the state‐of‐the‐art in this field and to address key questions with the intent of accelerating research and development efforts on all fronts. Highlights of the work presented and of the discussion and brainstorming sessions are provided here. It was the purpose of the organizers (The Orton Ceramic Foundation and the Orton Chair in Ceramic Engineering at OSU) to establish this event as a service to the Ceramics community in the spirit the founder of the field of Ceramic Engineering, Dr. Edward Orton Jr.

Analytical simulation of effects of local mechanisms on tensile response of ceramic matrix minicomposites

A micromechanics-based method based on a fiber shear lag analysis was developed to analyze the fast-fracture response of uncoated ceramic matrix minicomposites. The model was applied to two SiCf/SiC fiber minicomposite systems that were fabricated by Rolls-Royce High Temperature Composites, Inc., and the University of Connecticut. The analysis approach accounts for the fact that on average, the cracks in an actual minicomposite often have an irregular geometry. The effects of local variations in the fiber volume ratio on the composite response were also investigated. Parametric studies were performed to investigate the effects of the interfacial shear stress, global fiber volume fraction, and percentage of the composite that remains uncracked on the proportional limit stress and the composite secondary modulus. This work will facilitate an increased understanding of the key material mechanisms that take place during fast-fracture loading.

Temperature-dependent carbothermally reduced iron and nitrogen doped biochar composites for removal of hexavalent chromium and nitrobenzene

Synthesizing new composites with better efficiency and stability from abundant sources offers an appealing prospect for removal of heavy metals and organic pollutants to address water pollution concerns. In this study, iron (Fe) and nitrogen (N) doped biochar (BC) composites were investigated for hexavalent chromium (Cr(VI)) and nitrobenzene (NB) removal. Specifically, temperature-dependent Fe1-N1-BC1 composites were synthesized with different mass ratios of FeCl3 as Fe, melamine as N, and pinewood sawdust (PWS) as BC precursors via carbothermal reduction at 300, 500, 700, and 900 °C. Detailed characterizations indicating low-temperature incorporated superior N and high-temperature incorporated more Fe species in Fe1-N1-BC1 composites. The Cr(VI) and NB were removed with Fe1-N1-BC1, and experimental results attested with standard isotherm and kinetic models. The N species (pyridinic-N, pyrrolic-N, graphitic-N, quaternary-N, and oxidized-N) and Fe species (Fe3C, Fe0, Fe 2p 3/2, and Fe 2p 1/2) in temperature-dependent Fe1-N1-BC1 composites participated in pollutants removal. Mass ratio of 1:1:1 of Fe, N, and BC was effective, and under optimum conditions, low-temperature (Fe1-N1-BC1-300) and high-temperature (Fe1-N1-BC1-700) composites completely removed Cr(VI) and NB, respectively. In comparison to pinewood sawdust BC (PWBC) and composite of FeCl3 with PWS (Fe-BC), melamine with PWS (N-BC), and FeCl3 with melamine (Fe-N), the Fe1-N1-BC1 was more efficient due to synergistic effect of Fe, N, and BC for better pollutant interaction and removal. Effect of different factors on pollutants removal with Fe1-N1-BC1 was studied to reveal removal mechanism insights. Additionally, Fe1-N1-BC1 showed better efficiency in simultaneous removal of Cr(VI) and NB, stability for > 4 months, reusability, and applicability for multiple pollutants. This study offers a benign approach for synthesizing and applying Fe1-N1-BC1 for pollutants removal and exploring reaction mechanisms.

Domination of phononic scattering in solid solutioning and interfaces of HfB2–ZrB2 – SiC -carbon nanotube based ultra high temperature composites

HfB2-ZrB2 based ultra-high temperature ceramics (UHTCs) are used as protective tiles for nose cones and leading edges of the hypersonic vehicles that face harsh service conditions of temperatures >2000 °C. The present work assesses the effect of SiC (20 vol.%) and carbon nanotubes (CNT, 6 vol.%) incorporation on isolating the phononic and electronic contribution to thermal conductivity of spark plasma sintered HfB2-ZrB2 based UHTCs. Except HfB2-SiC, all ZrB2 based UHTC composites elicited similar electrical conductivity (∼ 5.7 × 106 S/m), whereas a marginal increase of ∼9% in thermal conductivity was observed with CNT reinforcement in HfB2-ZrB2–SiC composites. With HfB2/ZrB2-SiC composites eliciting high thermal conductivity (120–150 Wm-1K-1), the current work emphasizes the domination of phononic scattering (by ∼44%) due to solid solutioning in HfB2-ZrB2-based ceramics. Further, electronic thermal scattering events may only be marginal at interfaces of CNT and ZrB2, and limit thermal scattering in HfB2/ZrB2-SiC-CNT based UHTCs for hypersonic applications.

High Temperature Composites From Renewable Resources: A Perspective on Current Technological Challenges for the Manufacturing of Non-Oil Based High Char Yield Matrices and Carbon Fibers

During last decades a plethora of high temperature materials have been developed to work as a Thermal Protection System (TPS). Carbon based materials such as graphite, which possesses low density, high heat capacity and high energy of vaporization, have been used as TPS material. However, graphite has relatively poor mechanical properties, but exhibits low resistance to the thermal shocks. Accordingly, to bypass the limitation of graphite, carbon fibers are typically introduced in a carbon matrix to produce Carbon/Carbon Composites (CCCs). Among the different families of TPS solutions, Polymeric Ablative Materials (PAMs), produced combining high char yield matrices - mainly phenolic resins - and Carbon Fibers (CFs) are used to manufacture Carbon/Phenolic Composites (CPCs) i.e. the most important class of fiber reinforced PAM. Carbon fibers are traditionally produced from Polyacrylonitrile (PAN), Rayon and Pitch. Some limited researches also aimed to use cyanate-esters, bismaleimides, benzoxazines matrices in combination with ex-PAN-CFs, ex-Rayon-CFs, and ex-Pitch-CFs. In our paper, after covering the science and technology of these state-of-the-art fiber reinforced TPS materials, a review of current challenges behind the manufacturing of new, high char yield matrices and carbon fibers derived from alternative precursors will be provided to the reader. In particular, the possibility to produce CFs from precursors different from PAN, Rayon and Pitch will be reported and similarly, the technology of non-oil based phenolics, bismaleimides, cyanate-esters and benzoxazines will be discussed. The effect of the use of nanosized fillers on these matrices will also be reported. More in detail, after a preliminary section in which the state of the art of technologies behind carbon/phenolic composites will be covered, a second part of this review paper will be focused on the most recent development related to non-oil based phenolics and biomass derived carbon fibers. Finally, an outlook focused on the maturity of the lab-scale protocols behind the researches at the base of these non-traditional raw materials from an industrial point of view will conclude this review paper.

Wide-bandgap fluorides/polyimide composites with enhanced energy storage properties at high temperatures

In advanced electronics and electrical power systems, polymer dielectric capacitors are favored for their high power density and great reliability. However, the low energy density at high temperatures constrains their use in emerging applications. To address this vital issue, herein, a novel calcium fluoride (CaF2) nanoparticle with a wide bandgap (∼12.1 eV) and moderate permittivity (∼10.0) is prepared by a simple direct precipitation method and then introduced into the polyimide (PI) matrix. The incorporation of the CaF2 nanoparticles increases the permittivity and reduces conduction loss simultaneously. Consequently, at 150 ℃, the PI film with 3 vol% CaF2 exhibits enhanced discharged energy density and breakdown field of 2.68 J cm−3 and 455.4 MV m−1, respectively. Besides, the composite shows a higher power density of 0.36 MW cm−3 and a faster discharge speed of 2.09 μs at 150 ℃ than that 2.93 μs of biaxially oriented polypropylene (BOPP) measured at 85 ℃. Notably, CaF2 nanofiller, as a deep trap, captures injected charges and alleviates the local electric distortion, as revealed by finite element simulation and thermally stimulated discharge current (TSDC) measurement. This work proposes a novel fluoride nanofiller to rationalize the energy storage improvement of high-temperature composites with potential wide application.

Effect of Interfaces on Thermal Stability of HfB <sub>2</sub>–ZrB <sub>2</sub> – SiC -CNT Based Ultra High Temperature Composites

Effect of Interfaces on Thermal Stability of HfB <sub>2</sub>–ZrB <sub>2</sub> – SiC -CNT Based Ultra High Temperature Composites

Negative Thermal Expansion HfV2O7 Nanostructures for Alleviation of Thermal Stress in Nanocomposite Coatings.

A primary mode of failure of thin-film coatings is the mismatch in thermal expansion coefficients of the substrate and the coating, which results in accumulation of interfacial stresses and ultimately in film delamination. While much attention has been devoted to modulation of interfacial bonding to mitigate delamination, current strategies are constrained in their generalizability and have had limited success in imbuing resistance to prolonged thermal cycling. We demonstrate here the incorporation of rigid thermal expansion compensators within polymeric films as a generalizable strategy for minimizing thermal mismatch with the substrate. Nanostructures of the isotropic negative thermal expansion (NTE) material HfV2O7 have been prepared based on the reaction of nanoparticulate precursors. The NTE behavior, derived from transverse oxygen displacement within the cubic structure, has been examined using temperature-variant powder X-ray diffraction, Raman spectroscopy, electron microscopy, and selected-area electron diffraction measurements. HfV2O7 initially crystallizes in a 3 × 3 × 3 superlattice but undergoes phase transformations to stabilize a cubic structure that exhibits strong and isotropic NTE with a coefficient of thermal expansion (CTE) = -6.7 × 10-6 °C-1 across an extended temperature range of 130-700 °C. Incorporation of HfV2O7 in a high-temperature thermoset polybenzimidazole enables the reduction of compressive stress by 67.3% for a relatively small loading of 26.6 vol % HfV2O7. Based on a composite model, we demonstrate that HfV2O7 can reduce the thermal expansion coefficient of polymer nanocomposite films, even at low volume fractions, as a result of its substantially higher elastic modulus compared to the continuous polymer matrix. By changing the volume fraction of HfV2O7, the overall coefficients of thermal expansion of the film can be tuned to match a range of substrates, thereby mitigating thermal stresses and resolving a fundamental challenge for high-temperature composites and nanocomposite coatings.