SiC Grains Research Articles

Unravelling the impact of palladium on ruthenium-induced corrosion of SiC coatings in TRISO particles

Ru and Pd are fission products released through SiC layer in TRISO fuel at high temperature. This study investigates the corrosion behaviour of Ru-Pd on SiC layers of tri-structural isotropic (TRISO) particles. Specifically, it explores the effects of Pd (strongly reactive FP) on Ru (weakly reactive FP)-induced corrosion. In Pd-Ru/SiC systems, a Ru-Pd-Si liquid phase forms at high temperatures even with minimal Pd, accelerating corrosion along SiC grain boundaries. Comparing Pd’s role in Ru/SiC and Ag/SiC systems underscores the importance of liquid phases in FP migration. A novel approach is proposed for predicting the corrosion effects of multiple FPs on SiC through enthalpic interaction analysis.

In situ synthesis, mechanical properties, and reaction mechanism of the WB2–SiC composites

AbstractIn the present work, WB2–SiC composite powders containing 20 vol.% of SiC were in situ synthesized by the boro/carbothermal reduction with WO3, SiO2, B4C, and carbon black as raw materials at 1400°C, 1500°C, and 1600°C, respectively. The as‐synthesized composite powders were then consolidated by spark plasma sintering (SPS) technique to obtain WB2–SiC composite bulk samples. The experimental results showed that the relative density of the WB2–SiC composite ceramic samples achieved in this study was higher than 97.5%. Also, electronic microscopy observations showed that SiO2 had reacted completely during the preparation process, and the SiC grains were homogenously embedded among the WB2 grains with the formation of a three‐dimensional structure. The Vickers hardness and fracture toughness values of the composite ceramic fabricated by powder heat treated at 1400°C were 24.6 ± 0.7 GPa and 5.4 ± 0.7 MPa·m1/2, respectively, which were the highest among three samples prepared in this study.

Cutting mechanism of reaction-bonded silicon carbide in laser-assisted ultra-precision machining

Reaction-bonded silicon carbide (RB-SiC) is an important material used in aerospace optical systems. Due to the property mismatch between Si and SiC phases, the underlying cutting mechanism in ultra-precision machining of RB-SiC remains relatively unclear. Recently, laser-assisted machining (LAM) has emerged as an effective technique to improve the machinability of hard and brittle materials, which brings the question that how the high temperature affects the machining mechanism of RB-SiC. To elucidate these aspects, a series of grooving experiments and MD simulations were conducted in this study. The interaction mechanism between phases on material removal and subsurface damage was revealed and the effect of cutting temperature on Si-SiC interaction was explored. The results indicate that in conventional ultra-precision machining, SiC grains could affect the deformation of Si phase, whereas the influence of Si phase on SiC deformation is limited. As the cutting temperature increases, the Si-SiC interaction is less apparent and the deformation of Si and SiC becomes more independent. Meanwhile, the prominence of phase property mismatch on subsurface damage are reduced while the extension of disordered phases into boundaries merges as an important mechanism in subsurface damage formation. This research helps to understand the thermal effect on material interaction between phases during machining and aid to improve the performance of LAM on RB-SiC.

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.

Wear mechanism of oxide-bonded SiC refractory tiles in the combustion zone of waste-to-energy facilities

Refractory tiles used in waste-to-energy facilities are exposed to high temperatures (Tflue-gas ≈ 1200 °C) and corrosive environment with gases and fly ashes. Post-mortem examination of refractory tiles from the combustion zone of waste-to-energy plants was conducted to understand the damage mechanism of the refractory material. Corroded refractory tiles from this area showed an important loss of matter and large cavities on the hot surface. Investigations highlighted the weakness of the refractory matrix of the material. In contact with slag deposit and corrosive gases, the bonding phase of the refractory material is dissolved and SiC grains are oxidized which causes the spalling of the hot face of refractory tiles.

Characterization of (Zr,Ti)B2-SiC composites obtained by hot press sintering of ZrB2-SiC-TiO2 powder mixtures

The ability to enhance mechanical and oxidation properties for severe environmental applications has led to substantial academic interest in multiphase ultra-high temperature ceramics (UHTC). The purpose of this work is to study the in-situ solid solution formation of (Zr,Ti)B2 from ZrB2 and TiO2 in a ZrB2-SiC composite using hot pressing reaction sintering. For this, a mixture of 10, 20, and 30 % vol% SiC with ZrB2 was mixed with 2.0 wt% TiO2. Hot pressing sintering was performed with a load of 20 MPa at a final temperature of 1850 °C/30 min in an argon atmosphere. The microstructures, crystalline phases, densities, mechanical properties, and oxidation resistance of the composites were examined and compared with ZrB2-SiC samples lacking TiO2. In samples where TiO2 was added, the matrix grain size slightly decreased, the fracture mode was mainly intergranular, and the SiC grain morphology changed the aspect ratio to be more equiaxed. The solid solution (Zr,Ti)B2 was produced, and it was demonstrated by EDS elemental map images and the XRD analysis that Ti atoms incorporate into the ZrB2 crystalline structure. The development of solid solutions showed no impact on relative densities or Vickers hardness. However, the solid solution formation favored an improvement in fracture toughness, probably owing to the smaller matrix grain size and intergranular fracture mode. Samples exhibiting (Zr,Ti)B2 formation presented lower oxidation resistance than undoped samples in the same oxidizing condition.

Galling-Free Forging of Titanium Using Carbon-Supersaturated SiC Coating Dies

The thermal chemical vapor deposition (CVD) process was utilized to fabricate 6H-structured SiC coating dies with carbon control. The carbon-rich clusters along the SiC grain boundaries acted as a pinning site to suppress irregular crystal growth and to homogenize the fine-grained structure. These massive carbon-supersaturated (MCSed) SiC dies with a thickness of 4 mm were utilized for upsetting pure titanium bars in dry and cold conditions. Under a stress gradient from the contact interface to the depth of the SiC coating, the carbon solute isolated from these carbon clusters diffused through the grain boundaries and formed free carbon agglomerates on the contact interface to the pure titanium bars. These in situ-formed free carbon agglomerates acted as a solid lubricant to sustain the friction coefficient at 0.09 at the hot spots on the contact interface and to protect the dies and bars from severe adhesive wearing.

Spark plasma sintering of hard wear‐resistant graphene nanoplatelet–reinforced TiB2 + SiC composites from TiC–B4C–SiC

AbstractGraphene nanoplatelet (GNP)–reinforced TiB2 + SiC composites were fabricated by reactive spark plasma sintering (SPS) from a TiC–B4C–SiC powder mixture with equal‐volume percentages, optimizing their SPS temperature and evaluating their unlubricated sliding wear against diamond. First, it is shown that during the heating ramp of the SPS cycle, TiC and B4C react according to the chemical reaction 2TiC + B4C → 2TiB2 + 3C, and that the thus‐formed C is graphenized as GNPs, leading to composites with microstructures consisting of a ceramic matrix of fine TiB2 and SiC grains with abundant randomly oriented GNPs at grain boundaries. It is also shown that this reactive SPS is optimal at 2000°C (under 75 MPa pressure and 5 min soaking), resulting in a very hard (∼28.5–29.9 GPa) and very tough (∼6.7(3) MPa m1/2) composite. And second, it is shown that these two properties and its proneness to develop an oxide tribolayer make this composite very resistant to unlubricated sliding wear against diamond (∼2.8(1)·108 (N m)/mm3), undergoing only very mild two‐body abrasion. Finally, opportunities for the fabrication of toughened and very hard ceramic composites for contact‐mechanical and tribological applications are discussed.

Microstructural evolution and phase transformation of cansas 3303 SiC fibers during thermal shock at 1200 °C

A self-built automatic platform was built to evaluate the thermal shock performances of Cansas-III SiC fibers at 1200 °C in air up to 500 cycles, the corresponding oxidation and damage mechanisms were then revealed. The results showed that oxide scale was formed during thermal shock with a thickness of about 1 μm, the core was not oxidized via its protection. The fiber roughness increased before 100 cycles due to the decomposition of the amorphous SiCxOy phase, and then decreased as the formation of oxide scale. Within Cansas-III SiC fibers, structural defects of free carbon increased as the increasing ID/IG values, in addition, the TO peak shifted to the left, which both demonstrated that the relative movements occurred among SiC grains and residual stresses were then emerged. To clarify the axis and radial cracking of the oxide scale, a modified formulation considering nonzero shear strain components was then proposed to calculate the related residual stresses. The peeling and cracking of the oxide scale was ascribed to the residual stresses of GPa level among SiC grains and the thermal expansion mismatch between the oxide scale and the core.

Microstructure, mechanical, and cutting performance properties of B4C and SiC reinforced sandwich composite segments

This study aims to extend the work-life of diamond-cutting segments and to economize the operating cost of diamond-cutting tools. In order to achieve this object, bronze matrix sandwich segments reinforced with SiC and B4C were produced utilizing the hot pressing technique. In the term of the cutting segments, it is favorable that the outer layers are wear-resistant and the middle layer is tough. SEM and XRD analysis were used to determine the microstructural properties. Mechanical properties were evaluated by conducting hardness, wear, cutting performance, and three-point bending tests. The cutting performance of the segments was determined by turning andesite marble. SEM examinations showed that SiC and B4C grains were homogeneously distributed in the bronze matrix. The highest hardness value was 113.9 HB in the B4C reinforced sandwich segment. The reciprocating wear test findings indicated that the matrix exhibited the lowest wear rate in the B4C reinforced sandwich composite segment, followed by the hybrid sandwich composite segment. The lowest amount of cutting loss after turning andesite stone was achieved in the SiC, and B4C reinforced hybrid sandwich composite segment. The cutting performance of the hybrid sandwich composite segment increased by 46.15 % compared to the conventional segment without additives. The highest value of the transverse rupture strength of the specimens was 380 MPa for the B4C reinforced sandwich composite segment and 352 MPa for the hybrid sandwich composite segment. Considering all the tests and analyses, the hybrid sandwich composite segment sample may be the most suitable for diamond-cutting tools.

The reinforcement of reaction-bonded boron carbide via adjusting SiC morphology controlled by carbon sources

Reaction-bonded boron carbide (RBBC) composites have great potential for large-scale industrial production owing to their low cost and flexible product size. In this work, RBBC composites with various carbon additions were fabricated by liquid Si infiltration. The morphology of carbon sources is decisive for the morphology of reaction-formed SiC grains at 1550 °C. The effects of carbon sources on the microstructure and mechanical properties of the composites were studied. The as-prepared composites achieve a flexural strength of up to 575 MPa and a fracture toughness of up to 5.1 MPa/m2. The enhancement of the strength and toughness was attributed to the formation of defects-containing nano-SiC grains and continuous ceramic skeletons composed of boron carbide and nano-SiC. In addition, high aspect ratio plate-like SiC grains also allow a considerable improvement in the mechanical properties, even if they are not uniformly distributed.

Densification, mechanical properties, and oxidation behavior of spark plasma sintered TaB2-SiC-BN composites

TaB2-30 vol% SiC binary and TaB2-SiC-BN ternary composites with varying hexagonal boron nitride (BN) ratios (1–3–5–7–10 vol%) were consolidated by spark plasma sintering at 1650℃ under 40 MPa for 5 min. The densification characteristics, phase formation, mechanical properties, and oxidation behavior of both the TaB2-SiC and TaB2-SiC-BN composites were investigated. No new peaks other than the characteristic peaks associated with the starting materials were observed. Among all compositions, that containing 27 and 3 vol% of SiC and BN, respectively, exhibited the highest densification, ∼99.9 %. Homogeneous heating during sintering due to the thermal conductivity of hexagonal BN, along with the reduction in porosity by BN entering between TaB2 and SiC grains improved the densification behavior of the ternary composites. Besides, the incorporation of BN led to significant improvements also on the fracture toughness, which increased by ∼46 %. In ternary composites, crack deflection and branching were identified to be effective toughening mechanisms. The addition of BN had a negligible effect on Vickers hardness when agglomeration was minimal. The oxidation resistance at 1100 and 1200 °C increased with the addition of BN.

Enhanced fracture toughness of high entropy boride by adding SiC

The effect of SiC content (10 vol%, 20 vol% and 30 vol%) and sintering temperature (1800 °C, 1900 °C and 2000 °C) on the microstructure and mechanical properties of high entropy boride-silicon carbide (HEB-SiC) composites were systematically investigated in this work. The densification was gradually increased with the increase of SiC content and sintering temperature. More specially, the densification of HEB-30 vol% SiC composite obtained at 2000 °C was as high as 99.1 %. As for the mechanical properties, the dense HEB-30S-2000 composite possessed the highest fracture toughness (5.24 MPa m1/2) and Vickers hardness (28.5 GPa). The above significantly enhanced fracture toughness was closely pertained to the fracture modes adjusting. In details, after the addition of SiC, the branching and bridging of crack, the rupture of large SiC grain, and the deflection of crack existing near the HBE matrix and SiC particles jointly promote the improvement of fracture toughness. Besides, the Vickers hardness increased linearly with the relative density increasing. A simplified equation was established, which could effectually reflect the linear connection between the Vicker hardness and relative density (SiC content) of HEB-SiC composites. It will certainly play an important guiding role in the further development of HEB-SiC composites.

A novel vinyl-bridged graphene oxide/polycarbosilane precursor for harsh environment-resistant ceramic temperature sensor

Ceramic temperature sensors are promising for automobile and jet engine monitoring but lack suitable materials and manufacturing methods. Herein, we designed and synthesized a novel vinyl-bridged graphene oxide/polycarbosilane (v-GO/PCS) hybrid precursor that could be easily shaped and pyrolyzed into reduced graphene oxide/silicon carbide (rGO/SiC) film as a stable and sensitive temperature sensor under harsh environments. As a result, 1 %-rGO/SiC ceramic film exhibited a fast response in the temperature range of 100 °C to 1000 °C. The rGO acted as a bridge linking the surrounding SiC grains, which significantly reduced the amount of thermal energy required for the directional transfer of electrons, leading to an increase in both the detection range and sensitivity of the sensor. The introduction of dry air, water vapor and acid (or alkali) atmosphere in the high-temperature conditions further verified its excellent stability. This work provides a simple and practicable strategy for highly stable temperature detection under harsh environments.

Isotope studies of presolar silicon carbide grains from supernovae: new constraints for hydrogen-ingestion supernova models

ABSTRACT We report isotope data for C, N, Al, Si, and S of 33 presolar SiC and Si3N4 grains (0.3–1.6 $\mu$m) of Type X, C, D, and N from the Murchison CM2 meteorite of likely core-collapse supernova (CCSN) origin which we discuss together with data of six SiC X grains from an earlier study. The isotope data are discussed in the context of hydrogen ingestion supernova (SN) models. We have modified previously used ad-hoc mixing schemes in that we considered (i) heterogeneous H ingestion into the He shell of the pre-SN star, (ii) a variable C-N fractionation for the condensation of SiC grains in the SN ejecta, and (iii) smaller mass units for better fine-tuning. With our modified ad-hoc mixing approach over small scales (0.2–0.4 M⊙), with major contributions from the O-rich O/nova zone, we find remarkably good fits (within a few per cent) for 12C/13C, 26Al/27Al, and 29Si/28Si ratios. The 14N/15N ratio of SiC grains can be well matched if variable C-N fractionation is considered. However, the Si3N4 isotope data point to overproduction of 15N in hydrogen ingestion CCSN models and lower C-N fractionation during SiC condensation than applied here. Our ad-hoc mixing approach based on current CCSN models suggests that the O-rich O/nova zone, which uniquely combines explosive H- and He-burning signatures, is favourable for SiC and Si3N4 formation. The effective range of C/O abundance variations in the He shell triggered by H ingestion events in the massive star progenitor is currently not well constrained and needs further investigation.

Engineering of ceramic membranes with superhydrophobic pores for different size water droplets removal from water-in-oil emulsions

Superhydrophobic (SHB) ceramic membrane surfaces have proved their superiority in water-in-oil (W/O) emulsion separation. However, the construction of ceramic membranes with SHB pores remains challenging and the interaction between the SHB pores and water droplets is still unclear. Herein, by growing uniform ZnO nanoclusters (NCs) onto the SiC grains of a symmetric SiC ceramic membrane and then grafting with triethoxy(octyl)silane, a series of ZnO NCs@SiC membranes with SHB pores were prepared. Prior to secondary hydrothermal synthesis ZnO NCs, the small-sized ZnO nanoparticles (NPs) were grown onto the SiC grains via a sol–gel process. All the ZnO NCs@SiC membranes with SHB pores showed improved water removal performance from W/O emulsions compared with that of the pristine membrane. The optimal membrane with SHB pores displayed a pore size of 0.19 μm with a water contact angle of 163.96°. The smaller water droplets in W/O emulsions, the membrane pores are easier to be polluted. When separating a 1000 ppm W/O emulsion with a water droplet size of 500 nm at a transmembrane pressure of 0.5 bar, the water rejection reached 98.90 %, and the steady-state oil flux was 92.99 L·m−2·h−1. Based on the separation experiments, the separation mechanism was revealed. This work provides significant perceptions into constructing SHB pores of ceramic membranes, which might be useful for other possible applications.

Ablation behavior of microwave absorbing SiCf/Si3N4 composites containing ZrOC–SiCN matrix

The thermal protection materials of ultra-high speed aircraft need the stealth performance, and it require the microwave absorbing materials should have high ablation resistance to serve under extreme conditions (>2000 °C). In this work, amorphous ZrOC–SiCN and SiCN were introduced into the inter-bundle matrix of SiC fiber reinforced Si3N4 matrix composites to improve the ablation resistance while retaining the wave-absorbing properties. For SiCf/Si3N4, the SiC nanocrystallines in SiC fiber are oxidized into SiO2 and accumulate on the surface, and the Si3N4 matrix is first transformed into SiC grains and then the SiC grains are gradually ablated into spherical SiO2 in the ablation process. After the introduction of ZrOC–SiCN and heat-treated at 1500 °C, the ZrCN can be formed to increase the scouring resistance of each woven layer, and the oxide film with high viscosity also can be formed, preventing the fiber bundles from being blown away in the central region, leading to the decrease of mass and line ablation rate from 12.2 mg/s and 27.3 μm/s to 7.3 mg/s and 16 μm/s, respectively. Meanwhile, the minimum reflection coefficient of the composite decreases from −4.9 to −10.6 dB.

Interfacial modulation of SiC/TiC hybrid nanofibers for fabricating flexible ceramic electromagnetic wave absorbers

Titanium Carbide (TiC), characterized by its hardness, conductivity and thermal stability, can serve as a suitable additive phase for SiC nanofibers. TiC phase can improve the flexibility and electromagnetic wave absorption property of SiC nanofibers without sacrificing its high-temperature thermal stability. Herein, flexible SiC/TiC hybrid nanofibers with different Ti contents were fabricated by electrospinning and precursor infiltration pyrolysis. The introduction of Ti can not only generate conductive TiC phase, but also act as a catalyst to regulate the growth of SiC grains, so as to adjust the flexibility and electromagnetic properties of the hybrid nanofibers. At the optimal Ti precursor content of 4 wt%, the SiC/TiC-4 hybrid nanofibers exhibit a broad effective absorption bandwidth of 4.5 GHz with the thickness of 1.6 mm. The flexible SiC/TiC hybrid nanofibers This work can provide a reference for the design of flexible ceramic nanofiber absorbers and is expected to enable practical application in high temperature conditions.

Spark Plazma Sinterlenmiş Cu-SiC Kompozitlerinin Fiziko-Mekanik ve Elektriksel Özelliklerinin Değerlendirilmesi

In this study, SiC reinforced Cu matrix composites were produced by spark plasma sintering to provide rapid consolidation and to prevent weak interfacial bonding and grain growth, undesired phases at the interphase region. In addition, the influence of the reinforcement ratio (vol.% 10, 20, 30) and particle sizes (1, 11, 24 µm) on the physico-mechanical (density, hardness) and electrical characteristics of copper composite materials was aimed. The bulk density values were determined by Archimedes’ method, SEM, EDS, and XRD analysis were used to identify microstructural factors and phase analysis. It was found that the selection of the appropriate sintering regime is very important for composite samples to reach nearly fully dense Cu-SiC composites with proper interfacial bonding between Cu and SiC grains without the formation of any undesired phases, results in very high relative density (min. 99.48%), low total porosity (0,15-0,52), good hardness (HV 122-186) and electrical conductivity. When fine SiC grains (~1 micron) are used and the amount of SiC increases, the hardness value of the composites was effectively improved without much loss in electrical conductivity. In this respect, this study provides an effective solution for the production of Cu-SiC composites with excellent combined performance.

Structural and Mechanical Properties of SiC-Rich By-Products of the Metal Grade Si Process

Mechanical properties of composites produced from the SiC-rich furnace slag using traditional stone and ceramic machining technologies were studied. A non-uniform mixture of coarse monocrystalline SiC grains soaked with Si-metal and glassy oxide phases represented the microstructure of dense monolithic SiC-rich samples. The fracture mechanism of coarse-grained SiC-rich composites was susceptible to the grain size/sample geometry and machining conditions yielding flexural strength in the range of 50-106 MPa and high compression strength of 750 MPa. Despite inhomogeneous macro and microstructure, mechanical and thermal properties are comparable to the traditionally produced siliconized SiSiC ceramics. It opens up the opportunity for the circular economy and value-added recycling of the Si/FeSi industries’ wastes.