Ceramic-based Composites Research Articles

Measuring thermal conductivity of materials at room temperature in atmosphere by using a continuous-wave laser and neural network model

To measure the thermal conductivity (TC) of materials at room temperature in the atmosphere via a continuous-wave laser, a new model differing from the existing heat transfer models for calculating the TC was constructed by combining a neural network (NN) with the finite element method (FEM). Massive FEM samples simulating the heat conduction process of specimens were generated to realise feature engineering and constructing an NN model for TC prediction. The accuracy of the NN model was validated through the experimental data of several samples measured using a self-developed apparatus equipped with a continuous-wave laser source. The maximum relative error between the predicted and real TC values was approximately 6%. The presented NN model is suitable for materials with thermal diffusivities less than 1 × 10−5 m2 s−1, corresponding to most ceramics and ceramic-based composites.

Artificial Nacre with High Toughness Amplification Factor: Residual Stress-Engineering Sparks Enhanced Extrinsic Toughening Mechanisms.

The high fracture toughness of mollusk nacre is predominantly attributed to the structure-associated extrinsic mechanisms such as platelet sliding and crack deflection. While the nacre-mimetic structures are widely adopted in artificial ceramics, the extrinsic mechanisms are often weakened by the relatively low tensile strength of the platelets with a large aspect ratio, which makes the fracture toughness of these materials much lower than expected. Here, it is demonstrated that the fracture toughness of artificial nacre materials with high inorganic contents can be improved by residual stress-induced platelet strengthening, which can catalyze more effective extrinsic toughening mechanisms that are specific to the nacre-mimetic structures. Thereby, while the absolute fracture toughness of the materials is not comparable with advanced ceramic-based composites, the toughness amplification factor of the material reaches 16.1± 1.1, outperforming the state-of-the-art biomimetic ceramics. The results reveal that, with the merit of nacre-mimetic structural designs, the overall fracture toughness of the artificial nacre can be improved by the platelet strengthening through extrinsic toughening mechanisms, although the intrinsic fracture toughness may decrease at platelet level due to the strengthening. It is anticipated that advanced structural ceramics with exceeding performance can be fabricated through these unconventional strategies.

Aluminosilicate glass-ceramics/reduced graphene oxide composites doped with lithium ions: The microstructure evolution and tuning for target microwave absorption

Ceramic-based composites are desirable lightweight materials for electromagnetic (EM) energy absorption. However, due to the lack of an effective electromagnetic wave attenuation mode, pure ceramics still face significant challenges in absorbing electromagnetic waves. It is still challenging to obtain advanced electromagnetic wave absorption (EMA) materials with low fillings, thin thickness, super absorption capacity, and effective absorption bandwidth (EAB) through clever microstructure design and appropriate multi-component strategy. Herein, a dielectric aluminosilicate/reduced graphene oxide (RGO) nanocomposite with different lithium content was constructed via a solvothermal sintering method. The microstructure and heterogeneous dielectric interface form perfect impedance matching, multiple polarization, coupling effects, and have excellent absorption performance. The absorbers display a minimal reflection loss (RL min ) of −51.95 dB by tuning the relaxation intensity, and the broadest covers all X band. In addition, the classic RCS simulation method to evaluate microwave absorption performance has practical application value in the field of radar stealth.

Process Modelling and Experimental Analysis of Optimal Specimen Selection in Organic CMCs

Bone grafting is a surgical restructuring procedure of replacing broken bones and reconstructing missing bone pieces so that complex bone fractures can be repaired to avoid any serious health risk as well as permanent bone disfiguration. Normally, human bones tend to regenerate and heal completely from fracture. But it needs a small scaffold to provide the necessary space to grow. Bone implants allow a broken bone to grow seamlessly. Traditionally, non-corrosive metal alloys are used for fixing broken bones. A metal plate is fastened between two ends of broken bones to join them. However, issues like high weight, high cost, low wear resistance, etc. led to the emergence of ceramics and ceramic-based composites in surgical engineering. Recent trends indicate the usage of organic ceramics and their associated composites as biomimetic materials for prostheses and other biomedical applications. This research paper deals with the fabrication of one such type of ceramic matrix composite (CMC) specimen with sea sponge and cuttlebone using powder metallurgy process by varying composition of cuttlebone, the particle size of the ceramics and sintering temperature of green compacts. Evaluation of thermo-mechanical properties and optimization of process parameters is carried out using the preferential selection index (PSI) method. The results obtained from this technique are further validated using Multi-Level General Factorial Design (MLGFD).

Ultra-high temperature resistance of one-dimensional hafnium carbide wrapped with pyrolytic carbon up to 2450 ℃

Hafnium carbide (HfC) have attracted growing interests from research of ultra-high temperature ceramics (UHTCs) field. In this paper, we investigated the synthesis and high temperature stability of one-dimensional (1D) HfC and the core-shell HfC nanwoires/pyrolytic carbon (HfCNWs/PyC). Results exhibited that HfCNWs with diameter of 200–300 nm could keep their morphological and structural stability at 2100 ℃, and PyC improved the stability of HfCNWs under high temperature conditions. Our work could not only provide theoretical basis for HfCNWs reinforced carbon or ceramic-based composites, but also propose a deep thinking of the stability of nanomaterials under ultra-high temperature conditions.

Synergistic effect of dielectric resonance and plasma oscillation on negative permittivity behavior in La1-xSrxMnO3 single-phase ceramic

Ceramic-based composites with negative permittivity property can be realized by dielectric resonance or plasma oscillation, but it is still a challenge to integrate two kinds of negative permittivity into a single-phase material. In this study, the La1-xSrxMnO3 (LSMO) single-phase ceramic (x = 0.3, 0.4, 0.5, 0.6 and 0.7) was successfully fabricated by a sol-gel auto-combustion and pressureless sintering method. Just by adjusting the content of Sr2+, the Lorentz-like and Drude-like negative permittivity were simultaneously observed in LSMO ceramic under the synergistic effect of dielectric resonance and plasma oscillation. The amplitude of dielectric resonance was lessened because of the increase of damping factor, and the resonance frequency gradually moved to a lower frequency region with the increase of Sr2+. When the content of Sr2+ reached 0.7, the Drude-like negative permittivity played an overwhelming role due to an enhanced double-exchange effect in La1-xSrxMnO3. Meanwhile, the tanδ of LSMO was as low as 0.085, which was scarcely observed in previous investigations. The generation and regulation mechanism of negative permittivity was further clarified. This work opened up a way to adjust negative permittivity behavior in single-phase ceramic material which has great value in high-power microwave filters and wireless ring resonators.

Cold sintered composites consisting of PEEK and metal oxides with improved electrical properties via the hybrid interfaces

The manipulation of interfacial structures offers an effective route to improve the physical and chemical properties of materials. However, it is challenging to design ceramic-based composites with hybrid interfaces involved with organics and inorganics through the conventional sintering technique, due to the incompatibility of these materials at high temperatures. Here, we propose a strategy to integrate poly-ether-ether-ketone together with several metal-oxide additives into zinc oxide (ZnO) to form composite varistors via cold sintering process. Nanoscale layers of hybrid additives are dispersed between densified ZnO grain structures forming Schottky barriers, which dramatically improves the electrical properties of the resulted composites. Compared with pure ZnO, the breakdown electric field at 0.1 mA mm −2 reaches over 13 kV mm −1 . Particularly, the composite shows a switch-like effect similar with switching devices, with an extraordinarily high nonlinear coefficient of 375. In addition, the elastic module decreases with the addition of PEEK. Given the flexibility in the dopants of polymers and metal oxides, this work provides a unique route to design composite materials with superior performances.

Research on hole depth in femtosecond laser deep micropore processing technology based on filament effect

Ceramic-based composites have been applied to turbine components of new-generation aerospace engines due to their excellent properties. Despite the superior high-temperature resistance of SiC/SiC composites, it is necessary to combine with film cooling technology to guarantee normal function of turbine components. However, SiC/SiC composites are typical difficult-to-process materials，and the depth of film cooling holes have increasingly high requirements, which have become one of the major problems in the manufacturing of aerospace engine turbine parts. In this paper, the spatial energy density distribution based on filament effect of femtosecond laser was theoretically studied, it is revealed that the filament effect of femtosecond laser with high single pulse energy will lead to the peak of energy density shift towards the negative defocus direction. Based on the theoretical research, the experimental study on the processing of deep micropore in SiC/SiC composites by femtosecond laser was carried out, main results show that in equal conditions, the depth of micropore in feed trepanning is deeper than that in trepanning, and that in trepanning is deeper than that in direct punching. This research provides both theoretical and technical support for processing of micropore with high aspect ratio by ultrafast laser on the difficult-to-process materials, which have high practical value in the aerospace field.

Ceramic Cutting Materials and Tools Suitable for Machining High-Temperature Nickel-Based Alloys: A Review

Nickel-based superalloys are attractive to many industrial sectors (automotive, military, energy, aerospace, etc.). However, their physical properties make them difficult to machining using traditional tools. Therefore, new materials for the machining of Ni-based alloys are required. Ceramic-based composites could act as a tool to replace the current materials. The incentives for this paper are to provide an overview of existing ceramic composites and draw some conclusions that will help in solving the problem of choosing materials for the processing of Ni-based superalloys. Despite the diversity of ceramic composites in this work, the possibility of using the SiAlON ceramic for Ni-based alloy machining is highlighted.

Preparation and mechanical behaviors of multiscale SiC nanowires/carbon fiber reinforced silicon oxycarbide ceramic composites

3D-carbon fiber felts reinforced ceramic-based composites are considered as valuable structural materials due to their excellent high-temperature mechanical performance, low density and low thermal conductivity. In order to enhance the mechanical properties of the carbon fiber reinforced silicon oxycarbide (SiOC) ceramics, in-situ growth of SiCnws on the surface of carbon fiber via a simple precursor impregnation and pyrolysis method was proposed. As a result, nanoscale SiC nanowires and microscale carbon fiber felts reinforced SiOC ceramics were successfully fabricated. The results showed that the compressive strength of the composite increased by 369% and 173% after two PIP process in x/y and z directions, respectively. The enhanced compressive strength could be ascribed to the brittle fracture of SiCnws and CFs, and crack deflection.

Preparation of zinc oxide/poly-ether-ether-ketone (PEEK) composites via the cold sintering process

Appropriate preparation routes allow designing and improving the performances of ceramic-based functional composites. In this work, two powder-preparation methods enabled by the cold sintering process are utilized to fabricate unique ZnO-based varistor composites. The thermoplastic polymer, poly-ether-ether-ketone (PEEK), has been successfully integrated with ZnO to form dense ZnO-PEEK composites. With a dissolution method, PEEK particles can be homogeneously dissolved by the mixed solution of tetrahydrofuran and toluene and then form nanoscale thin grain boundaries after cold sintering process. In the direct mixing method, large PEEK particles are observed in the cold sintered samples. A Finite Element Method (FEM) analysis indicates that von-mises stresses concentrate at the grain boundaries of ZnO and at the interfaces of ZnO and PEEK, and these can be increased with the increase of PEEK particle sizes. The electrical properties have been improved with the addition of PEEK, and the cold sintered 95ZnO-5PEEK shows a high breakdown electric field (0.1 mA/mm2) of 3070 V/mm, and a nonlinear coefficient of 5. In addition, the conduction mechanism of the composites has been investigated using impedance spectroscopy. Overall, our work provides a strategy for the development of high-performance ceramic-polymer composites via cold sintering process.

Fabrication of barium titanate ceramics via digital light processing 3D printing by using high refractive index monomer

A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices.

A stereolithographic diamond-mixed resin slurry for complex SiC ceramic structures

Over the years, stereolithography has been successfully used to prepare complex, strong silicon carbide (SiC) structures. However, most raw materials are dark in color and therefore have broad-spectrum absorbing properties, making the curing steps during stereolithography highly inefficient. Here, diamond powders were mixed with a light-curing resin, yielding a slurry with excellent curability. The slurry was then used to prepare SiC-based composites with complex morphologies using pyrolysis and reaction melt infiltration (RMI) process. The influence of the diamond volume fraction in the slurry on each process stage was investigated. The infiltration of molten Si into diamond body during RMI was greatly enhanced compared to traditional carbon bodies. SiC ceramic-based composites with complex morphologies and a maximum strength of ∼460 MPa was prepared rapidly and efficiently. This study demonstrates the great potential of the slurry for efficiently manufacturing SiC-based composites in mechanical parts where high strength and complex structures are needed.

Toughening cemented carbides by phase transformation of zirconia

Yttria partially stabilized zirconia was introduced into WC-Co cemented carbides to enhance their mechanical performance. The hardness and fracture toughness were improved simultaneously with the addition of ZrO2. Particularly, the fracture toughness of the cemented carbides was significantly enhanced. The mechanism was mainly attributed to the stress-induced phase transformation of tetragonal ZrO2 to monoclinic ZrO2. This phase transformation introduced a compressive stress field and deflected the micro-cracks. In addition, the ZrO2 particles dispersed homogeneously in the WC skeleton and had good interfacial bonding with both WC and Co phases, which was beneficial to the mechanical properties of the cemented carbides. This study provides a new promising approach to break the trade-off between the hardness and fracture toughness of cemented carbides to achieve excellent comprehensive mechanical properties. The new strategy will be also promising to be applied in a variety of cermets or ceramic-based composites.

Design and strategy for next-generation silicon carbide composites for nuclear energy

Silicon carbide (SiC) ceramic-based composites continue to be attractive material options for fusion in-vessel components and fission reactor core structures because of their exceptional high-temperature capability and favorable neutronic properties. As performance data accumulates, the limitations of the current generation of nuclear-grade SiC composites are becoming more apparent. These limitations mainly involve strength degradation during high-dose neutron irradiation. This paper discusses several options for improving the performance of the next generation of SiC composites to enhance the radiation resistance, along with new experimental results on neutron irradiation resistance. The main emphasis is on the selection of the fibers and the design and development of alternative interphase layers for advanced composites.

Modeling for the electromagnetic properties and EMI shielding of Cf/mullite composites in the gigahertz range

The electromagnetic properties and EMI shielding effectiveness of Cf/mullite composites via the spark plasma sintering were intensively investigated in the gigahertz range (8.2–12.4 GHz). Experimental results have revealed excellent electromagnetic properties and a high value of EMI shielding effectiveness (nearly 40 dB) for Cf/mullite composites with 1.65 vol% carbon fillers at thickness of 2 mm. We quantitatively characterize the contributions of microstructural features to overall EMI shielding effectiveness using a micromechanics-based homogenization model. The EMI shielding effectiveness enhances with respect to the Cf volume concentration before the threshold. The increasing trend of EMI shielding effectiveness with respect to AC (alternating current) frequency can be attributed to enhanced conductivity at high gigahertz range. It is demonstrated that filler and frequency dependent interface effects are essential to obtain excellent electromagnetic properties of Cf/mullite composite. The present research can provide guidances for the design of ceramic-based composites applied in high-temperature EMI shielding devices.

Biocompatibility and bioactivity of hardystonite-based nanocomposite scaffold for tissue engineering applications

Bone injury, especially bone damages due to the removal of bone tumors, is one of the most important issues in the field of therapeutic research in tissue engineering applications. In this context, ceramic-based composites have attracted widespread attention since they have mechanical properties close to the natural bone, hence providing similar conditions for the extracellular matrix (ECM). Thus, in this study, hardystonite and diopside (HT-Di) scaffolds containing various diopside amounts from 5 to 25 wt% were prepared by the space holder method. The results revealed that the fabricated scaffolds contain 70%–75% porosity with a pore size of 300–500 μm and a compressive strength of about 0.54 to 1.71 MPa which is perfectly in the range of the compressive strength of the sponge bone. Noticeably, great apatite formation ability was observed in the scaffold with diopside, although the scaffold without diopside showed poor bioactivity. The MTT assay depicted that the inclusion of diopside into hardystonite scaffold resulted in dramatic enhancement in the MG-63 cell viability. Moreover, the scaffold with diopside offered greater cell attachment and spreading than the scaffold without diopside. Therefore, the synergistic effects of the scaffold with 12.5 wt% of diopside, including great mechanical characteristic, excellent bioactivity, and appealing biocompatibility enable it to be an appealing choice for bone tissue engineering applications.

High performance of hydroxylated BiFeO3/polystyrene composite films with enhanced dielectric constant and low dielectric loss

In today’s world, technology for capacitor applications have rapidly increased the interest for the development of perfect composite materials (polymers and ceramics) with enhanced dielectric properties. In the present work, the composites with bismuth ferrite (BiFeO3, BFO) particles as functional fillers and polystyrene (PS) as polymer matrix was prepared by solution casting technique. To improve the dielectric properties of the composites, the surface of BFO particles were chemically treated with H2O2 to introduce –OH groups. The experimental results show that the hydroxylated BFO-PS composites enhanced the dielectric constant, AC electrical conductivity and the dielectric loss is relatively suppressed. The surface hydroxylated BFO particles were more homogeneously dispersed into the PS matrix and it was confirmed by scanning electron microscopy (SEM). Moreover, the ferroelectric properties of the composites were significantly improved and a maximum remnant polarization (2Pr = 1.442 μC/cm2) was obtained in the composite materials as compared with BFO-PS at the same volume fraction of fillers. The thermal properties of the resultant composite films were investigated by using differential scanning calorimetry (DSC) method. The demonstrated approach may provide a route for using the hydroxylated ceramics to enhance the dielectric properties in ceramic-based polymer composites.

Improved piezoelectric performance and hydrostatic parameters of a novel 2–0–2–0 composite

A composite containing parallel-connected layers of a porous ferroelectric PZT-type ceramic and porous polymer is manufactured, and effective piezoelectric properties and hydrostatic parameters are first studied for 2–0–2–0 connectivity. An influence of air pores in different layers on the longitudinal (d33∗) and hydrostatic (dh∗ and gh∗) piezoelectric coefficients, and squared hydrostatic figure of merit dh∗gh∗ of the composite is analysed. Large values of d33∗ ≈ 400–600 pC/N, dh∗ ≈ 300–500 pC/N, gh∗ ≈ 100–150 mV m/N, and dh∗gh∗ ≈ (30–60)·10-12 Pa−1 suggest that this material has no analogs among ceramic-based composites and is suitable for piezoelectric sensor and hydroacoustic applications.

Additively manufactured mesostructured MoSi2-Si3N4 ceramic lattice

Lattice structures, their shape, orientation, and density make the critical building blocks for macro-scale geometries during the AM process and, therefore, manipulation of the lattice structure extends to the overall quality of the final product. This work reports on manufacturing of MoSi2-Si3N4 ceramic lattices through a selective laser melting (SLM) approach. The strategy first employs the production of core-shell structured MoSi2/(10-13 wt%)Si composite powders of 3–10 μm particle size by combustion synthesis followed by SLM assembly of MoSi2/Si lattices and their further nitridation to generate MoSi2-Si3N4 mesostructures of designed geometry. Experimental results revealed that the volumetric energy density of SLM laser has remarkable influence on the cell parameters, strength, porosity and density of lattices. Under compressive test, samples sintered at a higher laser current demonstrated a higher strength value. Selective laser melting has shown its potential for production of cellular lattice mesostructures of ceramic-based composites with a low content of a binder metal, which can be subsequently converted into a ceramic phase to produce ceramic-ceramic structure.