SiC Ceramics Research Articles

A Combined Stereolithography and A Pressureless Sintering Method to Prepare SiC Ceramics

The use of submicron silicon carbide powder as a raw material is crucial for preparing high-performance silicon carbide ceramics. However, its strong absorption of ultraviolet light makes stereolithography of submicron silicon carbide powder challenging. In this study, submicron SiC particles, photosensitive resin, and photoinitiator were used as raw materials to prepare SiC ceramics via stereolithography combined with a pressureless sintering method. The effects of ultraviolet wavelength, type, and content of photoinitiator on the curing properties of submicron SiC ceramic slurry were investigated. The results showed that the curing thickness of the SiC ceramic slurry significantly increased with the increasing ultraviolet wavelength. Compared to photoinitiators TPO and 396, photoinitiator 819 exhibited a better curing effect. Additionally, increasing the photoinitiator content facilitated the generation of more free radicals in the SiC ceramic slurry at low light intensity, thereby improving its ultraviolet absorption characteristics. When the dosage of photoinitiator 819 was 8.8%, the SiC slurry achieved the best curing performance, with a single-layer curing thickness of 50 μm and a sintering density of 95% for SiC ceramics.

A Review on High-Performance SiCf/SiC Composites Prepared by PIP Process

Silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiCf/SiC) are considered as a promising material for aero-engine hot-end structural components. The polymer infiltration and pyrolysis (PIP) process offers the benefits of high cost-effectiveness, adjustable preparation temperatures, and the ability to fabricate components with complex shapes. The manufacture of high-performance SiCf/SiC composites using the PIP process has become a research focus. This review briefly generalizes the synthesis methods of polycarbosilane and the specific process of polycarbosilane converting into SiC ceramics during pyrolysis. In addition, the physical and mechanical properties of SiCf/SiC composites prepared by the PIP process in recent years are discussed. Furthermore, this review summarizes some improvements to address the shortcomings of the PIP process, including adding fillers and combining other processes to assist the PIP process. At last, the future development trend of high-performance SiCf/SiC composites prepared by the PIP process is prospected.

Reactive Spark Plasma Sintering and Oxidation of ZrB2-SiC and ZrB2-HfB2-SiC Ceramic Materials

This study presents the fabrication possibilities of ultra-high-temperature ceramics of ZrB2-30 vol.%SiC and (ZrB2-HfB2)-30 vol.% SiC composition using the reaction spark plasma sintering of composite powders ZrB2(HfB2)-(SiO2-C) under two-stage heating conditions. The phase composition and microstructure of the obtained ceramic materials have been subjected to detailed analysis, their electrical conductivity has been evaluated using the four-contact method, and the electron work function has been determined using Kelvin probe force microscopy. The thermal analysis in the air, as well as the calcination of the samples at temperatures of 800, 1000, and 1200 °C in the air, demonstrated a comparable behavior of the materials in general. However, based on the XRD data and mapping of the distribution of elements on the oxidized surface (EDX), a slightly higher oxidation resistance of the ceramics (ZrB2-HfB2)-30 vol.% SiC was observed. The I-V curves of the sample surfaces recorded with atomic force microscopy demonstrated that following oxidation in the air at 1200 °C, the surfaces of the materials exhibited a marked reduction in current conductivity due to the formation of a dielectric layer. However, data obtained from Kelvin probe force microscopy indicated that (ZrB2-HfB2)-30 vol.% SiC ceramics also demonstrated enhanced resistance to oxidation.

Preparation of biomorphic porous SiC and SiO2 ceramics by sol infiltration into biotemplate followed by controlled sintering

Preparation of biomorphic porous SiC and SiO2 ceramics by sol infiltration into biotemplate followed by controlled sintering

Theoretical investigation of multipulse femtosecond laser processing on silicon carbide: ablation, shielding effect, and recast formation

In this study, we propose a transient multi-physics coupling model for ultrafast laser ablation based on the material point method (MPM). By employing the continuum assumption for material, heat transfer equation and particle phase change, as well as spatial discretization of the model, we achieve simulations of various coupled physical phenomena such as material temperature, phase change, stress, and recast layer formation. In terms of time, we simulate laser processing processes with up to 1000 pulses. The model is validated by comparing with experimental results on ablation morphology, recast layer formation from melted particles, and surface oxidation. The proposed model accurately captures the multi-physics aspects of ultrafast laser ablation processes in SiC ceramics. The experimental validation confirms the model’s reliability and offers valuable insights into the underlying physical phenomena.

The non-destructive control of mechanical properties of ceramics on the silicon nitride and silicon carbide based by acoustic emission method

The acoustic emission (AE) in reaction bonded SiC and Si3N4 ceramics and hot pressed Si3N4+TiN composites were investigated during the bending tests. A clear correlation between some AE parameters and specimen strength was established for all materials. Two methods for non-destructive control of materials strength have been proposed. High accuracy of control (error not more than 3%) in comparison with traditional estimation by sample average (error of 15% and higher) was observed.

The structural and mechanical properties of open-cell aluminum foams: Dependency on porosity, pore size, and ceramic particle addition

Aluminum foams are desired for lightweight, high-performance, and cost-effective materials, particularly in automotive, aerospace, and advanced power plants. Expansion of their applications depends on developing a detailed understanding of the structural and mechanical properties of aluminum foams. In this research, open-cell aluminum foams with 25.51–81.88 % porosity were manufactured through powder metallurgy using a space holder technique, with varying carbamide (urea) ratios (17–80 %) and particle sizes (1–1.4 mm, 1.7–2 mm, 2–2.4 mm). Three different ceramic particles, B4C, Al2O3, and SiC were used as reinforcement to improve the compression properties and energy absorption capacity of the foam materials. The study determined open and closed porosity ratios, spherical diameter, sphericity values, micropore sizes, mechanical properties, and energy absorption capacity of the foam samples both with and without ceramic additives. The results show that porosity ratio, pore size, and ceramic particle addition significantly affect aluminum foams' structural and mechanical properties, allowing for tailored properties for specific applications. It was observed that as porosity increased, compressive stress decreased, and the length of the plateau region and the shape change where densification began increased. However, there was no significant change in compressive stress and specific energy values with changing pore size. The optimal B4C addition was found to be 4 %, which significantly improved compressive strength to 3.75 MPa and specific energy to 4.24 MJ m−3.

Dense nine elemental high entropy diboride ceramics with unique high temperature mechanical and physical properties

Due to their huge composition space and superior performance characteristics, high entropy borides have garnered great interest in many fields, particularly where their high-temperature performances at high temperatures are critical. Herein, we first discovered that dense (Ti1/9Zr1/9Hf1/9Nb1/9Ta1/9V1/9Cr1/9Mo1/9W1/9)B2 (HEB9) ceramics prepared at 1850 °C showed an exceptionally low temperature coefficient of electrical resistivity (4.28 × 10−4 K−1), which is ∼38% of that of (Ti1/5Zr1/5Hf1/5Nb1/5Ta1/5)B2 (HEB5) and nearly an order of magnitude lower than those of previously reported ZrB2 and ZrB2-30 vol% SiC ceramics. Their mechanical, thermophysical properties at elevated temperatures were also investigated systematically. Although the thermal conductivity of HEB9 increased with elevated temperatures, it remained at a very low level (∼29 W/(m·K)) at 1273 K, nearly half that of HEB5. Interestingly, it is found that the thermal conduction of HEB9 and HEB5 was mainly contributed by electrons, suggeting their thermal conductivity could be roughly estimated from corresponding electrical conductivity values. Moreover, HEB9 exhibited a geometrically necessary dislocation density over 30 times greater than HEB5, likely contributing to its higher Vickers hardness and unique physical properties. Notably, the flexural strength of HEB9 at 1600 °C was even improved to 650.0 ± 86.3 MPa, compared to the value (559.7 ± 36.7 MPa) at room temperature without degradation, which was comparable to that of HEB5, although thermodynamic calculations indicated a lower melting point of HEB9 and grain boundary softening was occurred in HEB9 at higher temperatures. The excellent mechanical, electrical and thermophysical properties of HEB9 at elevated temperatures make it a competitive candidate for various high-temperature applications.

Hot oscillatory pressing of SiC ceramics with B4C and C as sintering additives

SiC ceramics with 0.5 wt.% B4C and 0.5 wt.% C as sintering additives were prepared by hot oscillatory pressure (HOP) and hot pressure (HP). The mechanical properties and microstructures of the resultant ceramics were investigated. The results showed that the oscillatory pressure could effectively suppress the abnormal growth of SiC grains and promote the formation of high-density dislocation and stacking faults. The hardness of SiC ceramics made by HOP at 2000oC reached 28.9 GPa, which was much higher than that (26.8 GPa) of the sample made by HP at the same temperature. The current study suggests that HOP is a promising technique for preparing high-performance SiC ceramics.

Joining of SiC ceramics by iridium: The interfacial phenomena and joint strength

A methodology for joining SiC ceramic parts using iridium foil was devised. The connecting layer was formed via a solid-state reaction at 1350 °C or via a transient liquid phase (TLP) at temperatures exceeding 1417 °C. The microstructure of the connecting layer formed via solid-state reaction exhibits temporal changes. The overall thickness of the layer remains approximately constant over time; however, the thickness of the carbon-free central part, composed of Ir and iridium silicides, decreases with time. The thicknesses of the porous carbon-containing sublayers located on either side of the central region demonstrate an increase. The greatest average flexural strength value was found to be 110 ± 6 MPa. The flexural strength values decrease with an increase in the holding time. This behavior can be attributed to the growth of a porous carbon-containing layer. The connecting layer, obtained via a transient liquid phase, is composed of IrSi and C. The layers on either side of the central dense IrSi part contain a number of pores and carbon inclusions. The SiC/SiC joints formed at 1425 °C and 1500 °C exhibit bending strengths of 66 ± 4 and 29 ± 4 MPa, respectively. These findings illustrate the potential of iridium to join monolithic SiC ceramic parts at relatively low temperatures.

Joining SiC ceramics with CaO-Al2O3-SiO2 mixed powder/glass based on induction heating

CaO-Al2O3-SiO2 mixed powder and glass were used as the joining materials to join SiC ceramics by induction heating in a joining temperature range of 1400–1600 °C under pressureless condition with heating and cooling rates of 100 °C/min. The joint prepared with CaO-Al2O3-SiO2 mixed oxide powder as joining material has the highest shear strength of 60.09 ± 6.22 MPa at joining temperature of 1500 °C, which contains triclinic CaAl2Si2O8 crystalline phase generated by chemical reaction in the holding process. In contrast, the joint produced with CaO-Al2O3-SiO2 glass powder at 1500 °C also has the highest shear strength of 75.76 ± 2.34 MPa, which contains hexagonal CaAl2Si2O8 and quartz generated through crystallization in the holding process due to rapid cooling rate of induction heating. In this study, the feature of mixed powder and glass joining by the induction heating technology was discussed to provide an effective and economic method for ceramic joining.

Low-temperature Microwave Sintering of Foam SiC for Mechanical Properties and Electromagnetic Absorption

In this work, the foam SiC ceramics were prepared by conventional and microwave sintering methods at 800 °C combined with organic template impregnation method. The microstructure, crystal structure, and mechanical properties of the samples were evaluated. Compared with conventional sintering, microwave sintering has obvious advantages such as more uniform element distribution, shorter sintering time, and better mechanical properties. Its bending strength and impact resistance reach 2.28 MPa and 4.9 kJ/m2, respectively. The dielectric constant and reflection loss of the samples were tested, and the samples sintered by microwave between room temperature and 500 °C showed better dielectric properties; as well as better microwave absorption performance at frequencies of 2-18GHz. The mechanism of microwave sintering has been elucidated, and the heating method of microwave from inside to outside is an important reason for the excellent mechanical and absorbing properties of materials.

Water vapor corrosion behavior of SiC-Al40Y ceramics fabricated by reactive melt infiltration and thermal diffusion

The corrosion resistance of Y-Al diffused SiC ceramics (SiC-Al40Y) at 1100-1300 °C was investigated. The results show that the weight gain curves comply with the parabolic fitting formula, then the oxidation rate constant and the activation energy were calculated to be 1.653×10-5 (1100 °C), 3.704×10-5 (1200 °C), 9.306×10-5 (1300 °C) mg2/cm4s and 154.7 kJ/mol. Compared with reported SiC (41-147 kJ/mol), the higher activation energy indicates the better corrosion-resistant performance. And it is found that the Y-Al diffusion layers can be transformed to corrosion-resistant YAlSixOy layers under corrosive atmosphere. Eventually, based on experimental results, the corrosion-resistant mechanism is analyzed: chemical potential gradient caused by preferential oxidation of Y-Al prompts the immigration of Y-Al from matrix to surface, gradually forming a continuous Y/Al-silicate layer on the surface and thus can hinder the further corrosion of H2O, O2.

Effect of boron on phase, nanostructure, and thermal stability of polycarbosilane-derived SiC ceramics

The current study explores the formation, evolution, and thermal stability of polymer-derived SiBC at high temperatures. It focuses on the phase evolution of SiBC ceramics derived from the doping of boron in an allyl-containing polycarbosilane preceramic polymer after 1200 °C to 1600 °C pyrolysis. Different SiBC ceramic monoliths have been obtained. Boron is incorporated into the carbon phase at lower pyrolysis temperatures but into both the carbon phase and the SiC lattice structure at high pyrolysis temperatures. B–C bonds form in SiBC and hinder the growth of graphitic carbon and SiC. Boron improves the densification and thermal stability of the SiBC ceramics. This work provides an improved understanding of boron effects in polymer-derived SiC nanostructures at high temperatures.

Effect of SiO2/AlOOH double-coated SiC powders on the properties of SiC ceramics by vat photopolymerization

Vat Photopolymerization (VPP) technology is expected to address the challenges of preparing high-strength, precise, and complex SiC ceramics. However, the poor printability of SiC powders and the low strength of the resulting SiC ceramics remain significant obstacles. To overcome these issues, this study proposes a SiO2/AlOOH double-coating method for modifying SiC powders. The effects of AlOOH content in the double coating on the properties of SiC powders, slurries, and ceramics were investigated. Additionally, the impact of sintering additives on the densification behavior and mechanical properties of SiC ceramics was examined. The results indicated that increasing the AlOOH content in the double coating decreased the UV absorption of the powders and increased the curing depth of the slurries, but also increased the viscosity of the pastes. Moreover, while increasing the AlOOH content in the double coating improved the densification and flexural strength of the ceramics, the effect was significantly less compared to optimizing the sintering additive. Using SiO2/AlOOH double-coated SiC powders containing 2.5 wt% AlOOH and 10 wt% Al2O3-Y2O3-MgO (mass ratio 1:8:1) sintering additives, SiC ceramics were prepared with a relative density of 91.1 ± 3.5 %, a Vickers hardness of 1685.6 ± 86.4 HV, and a flexural strength of 281.7 ± 14.4 MPa, much higher than that of other SiC ceramic prepared using the same process. This represents the highest flexural strength of SiC ceramics prepared by VPP technology to date, providing a new method for the preparation of high-strength SiC ceramics via VPP.

Tailored directional porosity in ceramic matrix composites (CMCs) for hypersonic applications

AbstractIn the field of hypersonic systems and their missions, the occurring flows impose extreme mechanical and thermal loads on the materials used. At the German Aerospace Center (DLR), extensive research is conducted in this area, ranging from design and specification to the development of suitable materials concluding with the proof of concept under realistic conditions in wind tunnels. In recent years, ceramic matrix composites (CMCs) have been investigated for specific aspects of hypersonics. These materials exhibit consistent mechanical behavior over a wide temperature range (up to 1600 °C), coupled with high damage tolerance and thermal shock resistance, distinguishing them from metals and superalloys. Particularly, special porous C/C–SiC ceramics (carbon-fiber-reinforced carbon with silicon carbide) enable innovative material applications for components in transpiration cooling, fuel injection, or boundary-layer transition control. The work presented focuses on the next generation of porous C/C–SiC ceramics currently in development. By deliberately modifying the textile preform, the resulting microstructure and pore morphology are influenced, allowing for control over both the total volume and the orientation of the pores. Relevant parameters influencing porosity have been determined based on the results, and an initial characterization has been conducted. It has been demonstrated that there is a preferred direction of porosity within the sample thickness (Z-axis), and in terms of hypersonic-relevant properties, an absorption coefficient of 0.58 for an acoustic wave at 500 kHz (static pressure of 15 kPa), as well as a length-specific flow resistance of 3.4 MPa s/m2 and an overall porosity of 12.25% were determined. Building upon these promising initial findings, the goal is to further expand the understanding of the parameters influencing porosity and to generate a tailored material for different application scenarios by correlating them with hypersonic properties.

Finite element modeling of thermal residual stresses in functionally graded aluminum-matrix composites using X-ray micro-computed tomography

Metal-ceramic composites by their nature have thermal residual stresses at the micro-level, which can compromise the integrity of structural elements made from these materials. The evaluation of thermal residual stresses is therefore of continuing research interest both experimentally and by modeling. In this study, two functionally graded aluminum alloy matrix composites, AlSi12/Al2O3 and AlSi12/SiC, each consisting of three composite layers with a stepwise gradient of ceramic content (10, 20, 30 vol%), were produced by powder metallurgy. Thermal residual stresses in the AlSi12 matrix and the ceramic reinforcement of the ungraded and graded composites were measured by neutron diffraction. Based on the X-ray micro-computed tomography (micro-XCT) images of the actual microstructure, a series of finite element models were developed to simulate the thermal residual stresses in the AlSi12 matrix and the reinforcing ceramics Al2O3 and SiC. The accuracy of the numerical predictions is high for all cases considered, with a difference of less than 5 % from the neutron diffraction measurements. It is shown numerically and validated by neutron diffraction data that the average residual stresses in the graded AlSi12/Al2O3 and AlSi12/SiC composites are lower than in the corresponding ungraded composites, which may be advantageous for engineering applications.

Oxidation behavior of SiC‐AlN ceramics exposed to dry oxygen and water oxygen environments at 1100–1300°C

AbstractThe corrosion of SiCf/SiC composites in gas environment threatens their long‐term service in aeroengines as hot‐end structure components. Addition of corrosion‐resistant phases into SiC matrix is a potential strategy to improve the service performance of SiCf/SiC materials. Here, AlN added SiC ceramics were prepared by reactive melt infiltration, and the effect of AlN phase on the oxidation resistance of the ceramics was emphasized. The oxidation tests were performed in dry oxygen and water oxygen atmospheres at 1100°C–1300°C, respectively. The oxidation mechanism was discussed based on the microstructure evolution of the oxide layer. The results show that the oxide layer is composed of aluminum silicate glass and Al2O3 flakes dispersedly distributed in the glass phase. As the temperature rises, the oxide layer gradually grows and thickens. Finally, a smooth and dense protective layer could be formed on the surface of ceramics to resist oxidation. This study can provide a profound insight to construct SiCf/SiC composites with excellent oxidation resistance.

Effects of Sm2O3 and TiO2 on the performance of MgAl2O4-Si3N4 ceramics for solar thermal absorber in concentrating solar power

Aiming to further improve the properties of novel MgAl2O4-Si3N4 ceramic used as solar thermal absorbing material in concentrating solar power, effects of Sm2O3 and TiO2 on performance of the composites were investigated especially the mechanisms of different additives on microstructure and high temperature stability. The results show that both additives can accelerate sintering, reduce sintering temperature, improve the density and high temperature stability via liquid phase sintering mechanism. Besides, TiO2 can form displacement solid solution with Al2O3 to promote the sintering process. Sm2O3 is more conducive to improving the bending strength due to its function of increasing the length diameter ratio of β-Si3N4. TiO2 is more favorable for improving solar absorption owing to the distinctive absorption spectrum and large number of cation vacancy caused by substitution of Al3+ by Ti4+. MgAl2O4-Si3N4 composites with Sm2O3 and TiO2 additives have better performance than MgAl2O4-Si3N4, Si3N4 and SiC ceramics prepared via the same procedure, which makes it a certain choice for solar thermal absorbing material.

SiC-BASED CERAMICS AS A CONTAINER MATERIAL FOR DEEP GEOLOGICAL DISPOSAL OF RADIOACTIVE WASTE

In this work the research of Cr-doped SiC ceramics as a promising material for containers for the deep geological disposal of radioactive waste was carried out. Samples were investigated using XRD, Raman spectroscopy, microhardness measurements, nanoindentation and corrosion resistance tests. Obtained results showed that addition of 0.3…0.7 wt.% of Cr improves the mechanical properties of SiC ceramics. Corrosion tests in distilled water at T = 90 °C and immersion time of up to 4300 h revealed that Cr addition slows down corrosion processes in SiC ceramics. The average dissolution rate of SiC(Cr) samples in water is quite low and does not exceed the value of 0.16 μm/year.