SiC Ceramics Research Articles

Preparation of high-strength silicon carbide by SLS-RS

One major limitation of selective laser sintering (SLS) plus reaction sintering (RS) SiC ceramics was the poor mechanical properties related to those of the traditional reaction sintered SiC due to the excess residual Si and C. TiC as a new carbon source in SLS was explored in this work to improve the performance of sintered SiC. It's found that TiC could react with liquid Si and form liquid TiSi2 during the processing, and then reduce the residual Si from 26.41 vol% to 0.53 vol% in the final products. As the content of TiC increased, the flexural strength of the sintered sample increased from 274.3 MPa to 434.6 MPa. The maximum value was reached when the TiC content was 25 wt%. Continuing to add TiC would generate more TiSi2, and the flexural strength of the sintered sample would decrease.

Effect of ZrO2 content on mechanical properties of SiC ceramics prepared based on digital light processing

Digital light processing (DLP) technology shows promise in addressing the challenges of preparing high-strength, precise, and complex SiC ceramic structural parts. However, the low strength of DLP-printed SiC ceramic parts remains a persistent issue. To address this, a nano-ZrO2 particle enhancement strategy is proposed. This study systematically investigates the effects of ZrO2 content on slurry viscosity, curing depth, microscopic morphology, and the mechanical properties of SiC ceramics. The results indicate that increasing the ZrO2 content raises the viscosity of the SiC slurry and decreases the curing depth, which can adversely affect the printing quality of SiC ceramic green bodies. However, a higher ZrO2 content significantly reduces pore defects in the sintered parts, improving densification and mechanical properties. This underscores the importance of optimizing ZrO2 content. The SiC sintered parts reinforced with ZrO2 particles exhibited outstanding properties, including a relative density of 91.1 ± 3.2 %, Vickers hardness of 996.4 ± 93.8 HV, and a flexural strength of 201.5 ± 11.4 MPa. This study provides a straightforward and effective method for producing high-strength SiC ceramics via DLP.

Effects of novel carbon sources additives on the solid-state sintering behavior and properties of SiC ceramics

To enhance the density of SiC and improve the purity of the SiC, carbon is frequently used as a sintering additive. SiC ceramics were prepared in this study by using various carbon sources (graphitic carbon microsphere, carbon black, and flake graphite) combined with B4C through spark plasma sintering (SPS) at temperatures ranging from 1800 °C to 1900 °C. Among the above carbon sources, the graphitic carbon microspheres were created by hydrothermal carbonization combined with catalytic graphitization. The influence of the carbon sources on the phase compositions, microstructure, physical properties, and oxidation resistance of the SiC specimens was investigated. The findings revealed that the SiC specimens prepared with graphitic carbon microsphere had a smaller crystallite size than those prepared with other kinds of carbon. The SiC specimens prepared with graphitic carbon microsphere displayed high relative density, hardness, fracture toughness, and remarkable oxidation resistance. This was attributed to the lower oxygen content, better dispersion, and higher chemical reactivity of graphitic carbon spheres. In terms of the oxidation resistance of SiC specimens, factors such as purity (residual carbon) and porosity were found to have a more significant impact than grain size. In general, the use of carbon sources with high reactivity and good dispersion is an effective method in preparing SiC ceramics.

Effect of different joining temperatures on IN600/SiC brazed joints

IN600 superalloy and SiC ceramics has been conducted using an active AgCuTi filler, and the composite joints were characterized using scanning electron microscopy coupled with energy-dispersive x-ray spectrometry (SEM–EDS). The results demonstrate successful joining by carefully selecting brazing temperatures and holding times to produce high-integrity joints. The interfacial microanalysis revealed the formation of TiC and Ti5Si3 near the SiC side due to the reaction between titanium, carbon, and silicon. On the IN600 superalloy side, a Ti-Ni compound (TiNi3) was formed as a result of titanium reacting with nickel. The typical microstructure of the brazing joint interface includes: TiC+TiNi3, TiC, Cu(s,s)+Ag(s,s) and TiC+Ti5Si3. Furthermore, the shear strength evaluation of the joints was also conducted at ambient temperatures using a shear test. The experimental findings showed that the sample exhibited the highest shear strength (38 MPa) when subjected to brazing at 910 °C for 10 min. Fracture occurred at the interface between the base material and AgCuTi filler at higher brazing temperature (930 °C).

Low-temperature fabrication of conductive SiC ceramics using SiO2-coated SiC nanopowder with Sc2O3 additive by spark plasma sintering

Low-temperature fabrication of conductive SiC ceramics using SiO2-coated SiC nanopowder with Sc2O3 additive by spark plasma sintering

Effects of adding Si3N4 whiskers to ZrB2–SiC ceramics on microstructure, mechanical properties and oxidation resistance

ZrB2–SiC–Si3N4w ceramics (ZSNw) were prepared via the hot-pressing sintering method. The bending strength and fracture toughness of ZSNw at room temperature reached to 520 ± 24 MPa and 5.2 ± 0.16 MPa m1/2, respectively. The enhancement in mechanical properties is attributed to the grain refinement and attenuation of grain boundary induced by the homogeneous distribution of Si3N4 whiskers. The oxidation resistance of ZSNw were conducted at 1500 °C in an air atmosphere. Remarkably, after 10 h of oxidation, ZSNw remained excellent strength and toughness reaching at 589 ± 26 MPa and 4.8 ± 0.12 MPa m1/2, respectively. This oxidation resistance of ZSNw was mainly attributed to the gain refinement induced by Si3N4 whiskers, which effectively reduced the voids within the ceramic matrix. Therefore, this process promoted the densification and homogenization of the SiO2 protective barriers, accompanied with hindering the inward permeation of oxygen and the outward release of oxides.

Parametric design and performance evaluation of TPMS porous vitrified bond diamond grinding wheel using digital light processing

Porous vitrified bond diamond grinding wheels are commonly used for grinding hard and brittle materials. However, uneven pore distribution and low porosity affect the grinding performance of the wheel significantly. In this study, three types of triply periodic minimal surface porous vitrified bond diamond grinding wheels—Gyroid, Diamond, and Lidinoid–were prepared through parametric designing and digital light processing 3D printing. The grinding wheel achieved a uniform distribution and an interconnected pore structure. The key to high-performance grinding wheel via stereolithography 3D printing lies in the preparation of the slurry with high solid loading, low viscosity and uniform stability. Hence, the effect of surface modifiers on the slurry, along with the effect of sintering temperature and the microscopic and mechanical properties, was investigated. By grinding the SiC ceramics, the material removal rate, grinding temperature, and surface roughness were compared to those achieved using a conventional solid-structure grinding wheel. The results show that the slurry with the highest solid content of 80 wt% (58 vol%) and viscosity of 4.21 Pa s (30 s−1) can be prepared using surface-modified particles. The diamond grinding wheel sintered at 680 °C exhibits the best comprehensive performance. A grinding wheel prepared using stereolithography 3D printing can achieve better surface roughness and lower the grinding temperature.

Li2O addition as a means of achieving low-temperature densification of SiC ceramic

In order to achieve low-temperature densification of SiC ceramic, β-SiC nanopowder was doped with Li2O together with Y2O3–Al2O3–MgO as sintering aids, and then spark plasma sintered at temperatures ranging from 1450 °C to 1600 °C for 30 min under 30 MPa pressure in argon. The densities, microstructures and mechanical properties of SiC ceramics were systematically investigated, in comparison to the counterparts sintered with Y2O3–Al2O3–MgO additives. Since Li2O has a low melting point, Li2O addition effectively decreased the formation temperature of liquid secondary phase, enabling SiC ceramics to obtain higher density and lower porosity after low-temperature sintering (T ≤ 1550 °C). Besides, Li2O addition was found to decrease the viscosity of liquid phase and enhance grain growth of SiC through dissolution-reprecipitation process. When sintered at 1550 °C, Li2O addition led to a remarkable increase of density from 3.03 g/cm3 to 3.21 g/cm3 for SiC ceramic. Meanwhile, the SiC ceramic with Li2O addition exhibited a high Vickers hardness of 22.75 ± 0.35 GPa and a good fracture toughness of 3.83 ± 0.27 MPa m1/2. The research results are expected to benefit the low-cost fabrication of SiC ceramics based on pressure-assisted sintering and alleviate the thermal damage of SiC fiber in hot-pressed SiCf/SiC composites.

Low-temperature sintering of SiC ceramics using a mixture of preceramic precursor and metal nanoparticles

Polymer infiltration and pyrolysis (PIP) has a limitation in increasing the relative density of SiC ceramics above 90 %. This is due to the blockage of open pore channels. In this study, a new process that incorporates Ni and graphite nanoparticles into SiC preceramic precursor is examined. Ni nanoparticles react with the SiC precursor to form low melting point nickel silicide phases which infiltrate into pores of the bulk without a blockage problem. In later infiltration cycles, graphite nanoparticles are added to convert the nickel silicide to nickel carbide and silicon carbide, which may prevent the deterioration of mechanical strength at high temperature. The relative density of SiC ceramics in this study increases to 92 % and above, which is higher than that of SiC ceramics prepared by the traditional PIP. The results of this study show a pathway to process high density SiC ceramics at relatively low sintering temperatures.

The oxidation behavior and corrosion mechanism of SiC matrix ceramics in a high temperature wet air environment

The oxidation behavior and corrosion mechanism of SiC ceramics were investigated at high temperatures ranging from 1000 ℃ to 1200 ℃ in wet environments (75 % water/25 % air). The results demonstrate the formation of protective SiO2 layers, which effectively inhibit further oxidation at 1000 ℃ and 1100 ℃. However, simultaneous oxidation and water vapor corrosion occur at 1200 ℃, leading to substantial weight loss and the development of numerous porous layers that can reach up to 30 μm after 10 h oxidation. The YAG phases in the SiC ceramics react with SiO2 to generate Y2Si2O7, Y2SiO5, and/or Al2Si2O7 phases during oxidation process, which exhibit enhanced corrosion resistance under wet environments.

Silicon carbide ceramics manufactured by digital light processing and low temperature sintering

The rapid development of additive manufacturing techniques enables the preparation of SiC ceramics with complex configurations; however, the high sintering temperature and defects-control are still great challenges during processing. Thus, SiC ceramics were prepared by digital light processing followed by liquid phase sintering using Al2O3–Y2O3 additives in this study. The photopolymerization of the SiC slurry, microstructures and mechanical properties of the sintered ceramics were investigated. The Al2O3–Y2O3 additives enhanced the curing ability of the photosensitive SiC slurries by reducing the absorbance and scattering of UV light. The liquid phase accelerated the densification of the ceramics by particles rearrangement and interfacial bonding. Thus, the flexural strength of the ceramics increased from 41.0 MPa to 62.8 MPa with sintering temperature increasing.

Research on dynamic mechanical properties and damage model of ceramic materials under multi‐axial stress

AbstractDue to their exceptional impact resistance, ceramics are extensively used in various fields. However, unavoidable pores, microcracks, and inherent defects can degrade the performance of ceramic materials. A damage model of SiC ceramics under passive confining pressure was constructed based on the Lemaitre strain equivalence principle and the Weibull distribution function. This paper presented a dynamic damage model for SiC ceramics subjected to passive confinement pressure based on the principles of damage mechanics. Additionally, the split Hopkinson pressure bar device was employed to investigate the compressive strength and damage evolution of SiC ceramics at various shock pressures and confinement degrees. The experimental results indicate that constraints can reduce the damage to ceramics. The metal sleeve increased stiffness when compressing the ceramic material, allowing the specimen to convert from brittle–plastic–brittle. When sufficient constraints can be provided, the peak strain decreases gradually with the increase of the impact air pressure. Experimental data showing good agreement with the proposed model validated and analyzed the established model. Thinner boundary constraints cannot maintain the stability of ceramic structures, thicker boundaries do not significantly improve performance, and thicker boundaries can cause more weak areas. This paper provides guidance for the design of encapsulated ceramic composite armor by quantitatively studying the constraint thickness.

Microstructure and mechanical behavior of TaxHf1−xC–SiC fabricated by reactive hot‐pressing: Effect of Ta:Hf ratio

AbstractTaxHf1–xC are promising candidates for many applications under harsh environments due to their unique properties. Up until now, low‐temperature densification is still a big challenge for these ceramics. Moreover, the effect of Ta:Hf ratio on microstructure development and mechanical behavior of the ceramics is not clear. In this work, highly dense TaxHf1−xC–SiC ceramics (x = 0.2, 0.4, 0.6, 0.8) were fabricated at 1700°C by a novel reactive hot‐pressing processing with 8 wt% Si as sintering aid, which present excellent mechanical properties. Fracture toughness of the ceramics is higher than 6.3 MPa·m1/2, with the highest toughness achieved in Ta0.6Hf0.4C–SiC (8.5 MPa·m1/2). With the increase of Ta content, hardness of the ceramics tends to increase, while the bending strength tends to decrease. The highest bending strength is achieved in Ta0.2Hf0.8C–SiC (637 MPa), and the highest hardness is achieved in Ta0.8Hf0.2C–SiC (17.6 GPa). This work lays the foundation for the composition design of TaxHf1−xC‐based ceramics and composites.

Preparation and characterization of medium entropy alloy CrCoNi toughened SiC ceramics

SiC is a promising structural material for future advanced nuclear energy systems. However, the inherent brittleness and difficulty of densification of SiC limits its practical application. In this study, medium entropy alloy (CrCoNi) reinforced silicon carbide composites (CCN/SiC) were sintered at 1950–2200°C by spark plasma sintering (SPS). The influence of CCN addition on the CCN/SiC composites was investigated in terms of microstructure, mechanical and thermal properties. The results show that SiC sintered at 2200℃ has the highest density, and the addition of 7.5 wt% CCN can significantly improve the fracture toughness of SiC. Transgranular fracture, crack deflection, and premature crack termination due to interfacial passivation are considered as potential toughening mechanisms. Although the addition of CCN can degrade the thermal conductivity of SiC ceramics, it has little effect on the structural stability of the SiC matrix at high temperatures.

Comparing the effects of different sintering aids on spark plasma sintering of SiC ceramics

In the present work, to improve the mechanical properties of silicon carbide different sintering aids were used. 2.5 wt% B4C, 2.5 wt% AlN, and TiC in the 5 to 7 wt% range were selected to manufacture the SiC-based sample via spark plasma sintering at 1700 °C. The results show that the use of 2.5 wt% B4C-2.5 wt% AlN additives increases the strength (1206 MPa) of the composite through the compressive stress created in the grain boundaries and decreases its fracture toughness (5.13 MPa.m1/2). But in the case of TiC-doped SiC, the toughness (7.09 MPa.m1/2) and density (3.18 g/cm3) of the sample increases compared to the pure SiC sample.

Experimental and numerical investigation on the ricochet of hard-core 7.62 small-calibre projectiles from the SiC and Al2O3 ceramic targets

The presented research concerns an experimental and computational investigation of the ricochet of small-calibre projectiles from ceramic tiles. The performed experimental tests were in situ observed by a multi-anode X-ray imaging and a high-speed camera. A detailed experimental verification of the geometrical conditions demonstrated that the projectiles' cores exhibit a similar behaviour dependent on the impact angle for two ceramic grades, Al2O3 and SiC. The experimental inquiry was complemented by a thorough numerical analysis of the failure of the investigated target/threat configurations using the Impetus Afea® software. The conclusions on the ricochet were reached based on the findings of the instrumented ballistic tests combined with advanced 3D numerical simulations, and it can be considered one of the few investigations on this phenomenon from ceramic surfaces.

Material Removal Mechanism of SiC Ceramic by Porous Diamond Grinding Wheel Using Discrete Element Simulation.

SiC ceramics are typically hard and brittle materials. Serious surface/subsurface damage occurs during the grinding process due to the poor self-sharpening ability of monocrystalline diamond grits. Nevertheless, recent findings have demonstrated that porous diamond grits can achieve high-efficiency and low-damage machining. However, research on the removal mechanism of porous diamond grit while grinding SiC ceramic materials is still in the bottleneck stage. A discrete element simulation model of the porous diamond grit while grinding SiC ceramics was established to optimize the grinding parameters (e.g., grinding wheel speed, undeformed chip thickness) and pore parameters (e.g., cutting edge density) of the porous diamond grit. The influence of these above parameters on the removal and damage of SiC ceramics was explored from a microscopic perspective, comparing with monocrystalline diamond grit. The results show that porous diamond grits cause less damage to SiC ceramics and have better grinding performance than monocrystalline diamond grits. In addition, the optimal cutting edge density and undeformed chip thickness should be controlled at 1-3 and 1-2 um, respectively, and the grinding wheel speed should be greater than 80 m/s. The research results lay a scientific foundation for the efficient and low-damage grinding of hard and brittle materials represented by SiC ceramics, exhibiting theoretical significance and practical value.

The Structure and Properties of the Promising Ultra-High-Temperature HfB2–HfC–SiC Ceramics Obtained from Heterophase SHS Powders

The Structure and Properties of the Promising Ultra-High-Temperature HfB2–HfC–SiC Ceramics Obtained from Heterophase SHS Powders

A novel high reactive initiator system of vinyl‐substituted hydridopolycarbosilane (VHPCS) for lower curing temperature and higher ceramic yields

AbstractVinyl‐substituted hydridopolycarbosilane (VHPCS) is widely studied for its low viscosity, abundance of active functional groups, rapid curing, and high ceramic yield. The curing reactions mainly involve the free radical polymerization of vinyl and hydrosilylation reactions, but these reactions typically require high temperatures such as 160–250°C. The curing behavior of VHPCS‐17 with a tert‐butyl peroxybenzoate/Nickel acetylacetonate (TBPB/NIAA) system is investigated using differential scanning calorimetry and in situ Fourier transform infrared. The properties of VHPCS‐17 with different initiator systems and VHPCS with different vinyl contents (under TBPB/NIAA system) are studied using thermogravimetric analysis and x‐ray diffraction. The results demonstrate that the TBPB/NIAA system can facilitate the free radical polymerization of vinyl; moreover, this system decreases the peak temperature of the curing reaction from 251 to 141°C and increases the ceramic yield from 80.49% to 89.88%. The ceramic yield of cured VHPCS increases gradually, reaching 89.88% when the vinyl content is 17%. The grain size of β‐SiC decreases continuously with the increase in vinyl content, while the high‐temperature oxidation‐resistant properties of SiC ceramics obtained from different VHPCSs are not negatively affected.

High temperature oxidation behavior of liquid phases sintered SiC ceramics with ZrB2 addition

The oxidation property of liquid-phase sintered silicon carbide (LPS-SiC) ceramics with ZrB2 addition was studied after oxidation test in air at 1400 °C. The results indicate that the addition of ZrB2 decreased the degree of polymerization (DOP) of the silicate networks in the oxide layer, suppressing the additional oxidation caused by residual bubbles in the oxide layer of LPS-SiC, which bypassed the layer and directly corroded the material internally. After 100 h of oxidation, the additional oxidation depth was found to be 125 μm in the sample without ZrB2 and 0 μm in those containing 10 wt% ZrB2. Simultaneously, the decrease in DOP facilitates the migration of crystalline phases. The generated ZrSiO4 can migrate and aggregate at the interface between the surface oxide layer and the SiC/ZrB2 matrix, forming a continuous ZrSiO4 barrier. This impedes the diffusion of the oxidant and enhances the oxidation resistance. However, an insufficient ZrB2 content leads to a discontinuous ZrSiO4 layer, thereby weakening its protective effect. Simultaneously, a decrease in DOP increases the rate of oxygen diffusion, resulting in an increase in the oxidation layer thickness. This study contributes to a better understanding of the failure mechanisms of LPS-SiC in oxidizing environments and provide a reference for the design of oxidation-resistant LPS-SiC materials.