SiC Whiskers Research Articles

Effects of SiO2-coated CNTs on the directional formation of SiC whiskers and improvement in the ablative resistance of polymer-matrix composites

As the development of hypersonic aerospace technology progresses, greater challenges are presented for solid rocket motors (SRMs) thermal protection, and the ablation performance of insulation materials needs to be further improved. Carbon nanotubes (CNTs) as a new type of reinforcing nano-filler, readily react with the oxidative components in the working gas during SRMs operation, limiting their excellent performance. In this study, we propose to coat the commonly used reinforcing filler, SiO2, on the surface of CNTs to suppress their susceptibility to oxidation and investigate the effects of adding CNTs, SiO2, and CNTs@SiO2 to the matrix on material properties. The results show that the addition of CNTs@SiO2 significantly improves the ablation resistance of the insulation material, with the linear ablation rate of M-@SiO2-2 being 56 % lower than that of M-SiO2-2. Based on the analysis of the material's antioxidation performance and the strength of the resulting char layer after ablation, the reasons for the improvement of ablation performance are discussed. By conducting high-temperature tube furnace tests, the composition and structure of the char layer at different temperatures are studied, and it is found that CNTs in the CNTs@SiO2 formulation can directly provide the carbon source required for the carbon thermal reduction reaction, promoting the directional growth of SiC whiskers. Based on these findings, an ablation mechanism is proposed.

Static and dynamic mechanical properties of aluminum nitride-silicon carbide whisker composites

AlN composites reinforced with SiC whiskers and Y2O3 sintering aids were fabricated using the hot-pressing technique to investigate static and dynamic mechanical properties. Microstructure analysis revealed that increasing SiC whisker content yielded grain refinement and decreasing relative density. The Vickers hardness increased from 10.29 to 14.47 GPa, while the fracture toughness improved from 3.03 to 4.39 MPa·m1/2 with 30 wt% SiC whiskers. A numerical approach for evaluating the dynamic modulus and loss factor is presented utilizing the wave propagation characteristics. The dynamic properties showed decreasing dynamic modulus and increasing loss factor with higher SiC content, attributed to increased porosity and interphase boundaries. Thermal conductivity, however, decreased from 139.53 to 49.95 W/m·K as SiC whisker content increased, primarily due to enhanced phonon scattering at grain and interphase boundaries. These findings suggest that AlN-SiCw composites are promising candidates for heat dissipation ceramic substrates, which offer superior mechanical strength and reliable thermal management.

Improved mechanical and tribological properties of (TiZrHfNbTa)C with the addition of silicon carbide whiskers

Dense (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C with up to 10 wt % SiC whisker were prepared by spark plasma sintering. The influence of SiCw on the microstructure development, mechanical and tribological properties has been investigated. Nanohardness of HEC and SiCw phases varied between 38 GPa and 40 GPa, and indentation modulus of elasticity was ∼605 GPa. The hardness of the composites increased from 22 GPa to 27 GPa and indentation fracture resistance from 3.55 MPa m1/2 to 4.59 MPa m1/2 with increasing SiCw content. The main toughening mechanisms were crack deflection, crack branching, and crack bridging. The system HEC +5 wt% of SiCw was found to possess the highest bending strength of 623 ± 25 MPa. The composites exhibited similar coefficients of frictions with around 0.3 and wear rates approximately 1.50 × 10−6 mm3/N⋅m at 5 N and 2.66 × 10−6 mm3/N⋅m at 25 N with positive influence of SiC phase on the wear mechanisms.

Performance of advanced ceramic round tools when turning Inconel 718

Nickel-based superalloys, like Inconel 718, are very attractive metals for aerospace applications due to their excellent mechanical properties and thermal stability. However, these materials pose a significant challenge to the metal machining industry due to their very low machinability, especially in terms of reduced tool life because of the high heat generated during cutting. Nevertheless, it can be improved using high-performing tools that retain their hardness when exposed to high temperatures, such as ceramic tools. In this context, the study aims to compare the performance of two advanced ceramic tools, namely an alumina ceramic tool reinforced with SiC whiskers and a Bidemics™ one, when turning Inconel 718 at different cutting speeds, using as a baseline a conventional coated cemented carbide tool. First, the three inserts were characterized in terms of topography, thermal conductivity, and hot hardness to fully understand their operational behavior. Then, turning trials were conducted showing that both the ceramic tools outperform the coated carbide one in terms of tool life, with Bidemics™ demonstrating the best performance among all. This can be ascribed to its very high hardness maintained even at high temperatures, as well as its moderate thermal conductivity.

Tribological performance and mechanism of the titanium fiber-SiC whisker hybrid reinforced aluminum matrix composites prepared by pressure infiltration

In this contribution, a Ti-6Al-4V fiber (Tif) and SiCw (SiCw) hybrid reinforced 5056 Al composites (Tif + SiCw/5056 Al) were fabricated, and the effects of SiC whisker contents on the microstructure, mechanical properties, and wear resistance were investigated. The mechanical properties and the hardness of the composites increased first and then decreased with the increase of SiCw contents. The optimal ratio of SiCw to titanium fibers is 3 wt%. The flexural strength of the optimal composites reached 533 MPa, and the fracture toughness reached 29.1 MPa • m1/2. Under a load of 40 N, compared with the Tif/5056 Al composites sample, the wear rate of the optimal composites sample decreased by 80.7%. The uniformly dispersed SiC whiskers promote the formation of a mechanical mixing layer (MML) on the friction surface; the wear mechanism mainly involves abrasive wear and adhesive wear.

Comprehensive characterization of spark plasma sintered ZrB2-SiCp-SiCw composite and its corresponding orthogonal cutting simulation

A composite consisting of 12.5 wt% SiC particles and 12.5 wt% SiC whiskers in a ZrB2 matrix (ZrB2-SiCp-SiCw) was produced using spark plasma sintering. The sintering process was carried out at a temperature of 1900 °C and a pressure of 40 MPa for a duration of 7 minutes. X-ray photoelectron spectroscopy analysis confirmed the presence of C-C, C-Si, O-B, O-Zr, O-Si, and Zr-B bonds. Scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses revealed the presence of silicon and carbon in the ZrB2 phase. The nano-indentation hardnesses and elastic moduli of ZrB2 and SiC were measured as 2104.58 and 2268.97 Vickers and 397.58 and 394.27 GPa, respectively, under a load of 100 mN and a loading rate of 0.4 mN/sec. The orthogonal cutting process of an Al6061 workpiece with a ZrB2-SiCp-SiCw cutting tool was simulated using DEFORM 2D software. The response surface method was used to develop a model to evaluate the relationship between cutting parameters (tool tip radius, cutting speed, and rake angle), cutting force, feeding force, and maximum temperature. It was found that cutting and feeding forces decrease with increasing cutting speed and rake angle, while increasing the tool tip radius increases these forces. The tool and workpiece endure a higher maximum temperature as the cutting speed and tool tip radius rise, but the maximum temperature drops as the rake angle increases.

Effect of sintering temperature on mechanical properties of WC-cBN-SiCw composites with multi-scale and multi-morphology toughening strategy

The binderless WC cemented carbide was synthesized with multi-scale and multi-morphology toughening strategy by Spark Plasma Sintering. The influence of sintering temperature on the mechanical properties of WC-cBN-SiCw was investigated. The result showed that the Vickers hardness and fracture toughness initially increase and then decrease with the increase of sintering temperature. As the sintering temperature reaches 1300℃, the best Vickers hardness and fracture toughness can be obtained, 12.8 GPa and 10.6 MPa.m1/2 respectively. The toughening mechanism can be attributed to the strong and weak mixed interface characteristic constructed by micro and nano particles, which induce crack deflection and crack bridging. Meanwhile, the adhesion of nanoparticles on SiC whisker enhances the resistance of whisker pull out, which promotes the consumption of fracture energy.

High-temperature mechanical performances of SiC whisker in-situ toughened 3DN C/SiC countersunk bolts prepared by chemical vapor infiltration

High performance bolts, made of continuous fiber reinforced silicon carbide composites (C/SiC), are crucial to the design and preparation of the hot-end C/SiC components with large complex structures both in aerospace and aeronautical fields. In this work, in-situ grown SiC whiskers were uniformly introduced into the porous laminated 3DN C/SiC countersunk bolt, in order to improve the brittle nature of the 3DN C/SiC threads. Results showed that 7 % increase of tensile strength of the 3DN C/SiC countersunk bolts was achieved via in-situ grown SiC whiskers, and a fatigue life of 106 cycles was also passed. The stud fracture morphologies indicated that the SiC whiskers grew within the woven pores and toughened the layered SiC matrix, so that the load transfer between the layered SiC matrix and carbon fibers was improved under tension. Further high temperature tests showed that the tensile and the shear strengths of the in-situ toughened 3DN C/SiC countersunk bolts were degraded to 64.74 % and 28.83 % at 1000 °C in air respectively. During the thermal exposure, the carbon fibers were largely consumed by oxidation, while the SiC whiskers grew slender and formed a fluffy layer to partially reinforce the SiC matrix. The synergy effect of SiC whiskers and carbon fibers to hinder crack propagation and to toughen the SiC matrix contributes to the above mechanical properties of the bolts.

Preparation of silicon carbide reticulated porous ceramics with enhanced thermal shock resistance and high combustion efficiency

As the most prospective media material for porous media burners, silicon carbide reticulated porous ceramic (SiC RPC) is required to possess a high porosity to fulfill efficient combustion, as well as exceptional thermal shock resistance to withstand the thermal stress generated during the start-up and shutdown processes. To achieve the strengthening and toughening of highly porous SiC RPC, three-layered struts were constructed, and in-situ whiskers were formed in SiC RPC through vacuum infiltration and sintering under a nitrogen atmosphere in this work. The results indicated that the three-layered struts were formed after the preform was conducted with vacuum infiltration, encompassing a mullite coating, a silicon carbide layer and a mullite inner layer. When Si powder and flake graphite were incorporated into the SiC slurry, numerous SiC whiskers were formed in situ within the SiC skeleton. The formation of SiC whiskers was attributed to the enhancement of SiC RPC, resulting in an increase in CCS from 0.22 MPa to 0.55 MPa. Additionally, the residual strength retention rate after water quenching at 1100 °C was elevated from 41.6 % to 70.2 %. Moreover, the SiC RPC containing SiC whiskers exhibited an impressively high porosity of 83 %, leading to a surface temperature of 688 °C and a heating efficiency of 16.4 °C/min during the combustion process.

Elucidating the effect of whiskers on microstructural, mechanical and wear properties of ceramic-metal composites for sports venues applications

Ceramic whiskers reinforced composites are widely used in electrical, medical, and constructional applications due to their desirable strengths, hardness, and wear characteristics. In this study, to examine the wear and friction characteristics, the pressureless infiltrated Cu–SiC composites with different content of SiC whiskers were roll bonded to Al layer. According to SEM images, the SiC whiskers were distributed across the microstructure although they were aligned along rolling direction. Incorporation of SiC whiskers to Cu matrix led to rise of composites’ strengths, young moduli, and hardness values. The measured values of Al and Cu–SiC layers increased from 50 HV to 135 HV in Al/Cu–SiC (5 wt%) to 57 HV and 159 HV in Al/Cu–SiC (15 wt%). Ductile type of fracture along with dimples, delamination, and debonding of whiskers appeared on fracture surfaces. However, more debonding of SiC whiskers was observed as SiC content increased. Accordingly, mass loss decreased and less adhesive wear mechanism was observed. The mass loss decreased from 6.3 mg in Al/Cu–SiC (5 wt%) to 5.2 mg in Al/Cu–SiC (15 wt%).

Digital light processing of high-purity SiC ceramic membrane support modified by SiC whisker

High-purity SiC ceramic membrane has gained tremendous attention in the treatment of various corrosive wastewaters. Additive manufacturing technique makes it possible to fabricate high-purity SiC ceramic membrane with complex configurations. Here, we proposed a route for the preparation of high-purity SiC ceramic membrane support using digital light processing and SiC whisker reinforcement. With the increase of whisker content, the viscosity of SiCw/SiC photosensitive slurry increased due to the formation of whiskers agglomerations; the average pore size shifted from 3.15 μm to 1.35 μm with the occupation of large pores by SiC whiskers. In addition, the compressive strength of the ceramic support increased from 10.7 MPa to 16.7 MPa because of the decline in pore size and the toughening effects by SiC whiskers. So, the introduced SiC whiskers enhanced the pore connectivity and mechanical strength of the porous ceramics. This work provides a feasible path to manufacture high-purity SiC ceramic membrane support with complex configuration, high pore-connectivity and excellent mechanical properties.

The synthesis of high sinterability (Zr, Hf)C and SiC hybrid nanocrystalline particles by sol-gel method

Multi-phase UHTCs are favoured for their superior ablation resistance and mechanical properties. In this work, to improve the efficiency and decrease the sintering temperature and pressure, the (Zr, Hf)C and SiC hybrid nanocrystalline particles were prepared via the sol-gel method combining carbothermal reduction at 1600 °C. Utilizing their high sinterability, a relative density of 96.1% (Zr, Hf) C–SiC composite was obtained at the conditions of 1900 °C and 30 MPa using SPS technology. XPS and FT-IR results demonstrate that Zr, Hf, and Si were successfully trapped in the cross-linking structure of the precursors. Precursors of Zr, Hf, and Si reached a molecular-level mixture in the gel phase. SEM, XPS, and XRD characterization showed that the Si–C bond was formed preferentially, leading to the emergence of SiC whiskers and SiC wrapped (Zr, Hf)C with increasing temperature. And, the (Zr, Hf)C can be easily generated during solid solution reaction. Eventually, a nanoscale mixture of (Zr, Hf)C and SiC particles was successfully obtained at 1600 °C. The hardness and compressive strength of the (Zr, Hf)C–SiC composite were 12.94 GPa and 622 MPa, respectively. Comparing usual sintering processes (over 2000 °C and 35 MPa), the reason for the improved sinterability can be attributed to the high sintering activity of the (Zr, Hf)C and SiC hybrid particles, and the existence of the solid solution and nano-SiC.

Physical, mechanical properties and microstructure of waste GBFS-based geopolymer incorporated with metakaolin and SiC whiskers(SiCw)

Geopolymer, known as alternative materials to ordinary Portland cement, possess superior properties. This study employed varying dosages of metakaolin from 0 to 30 % and silicon carbide whiskers (SiCw) from 0 to 0.05 % to enhance GBFS-based geopolymer matrix. The process began with the dispersion of SiCw in an alkaline activator through magnetic and ultrasonic stirring, followed by the preparation of the geopolymer. Physical and mechanical characteristics were evaluated to reveal the improvement effects of metakaolin and silicon carbide whiskers on the geopolymer. Techniques such as FTIR, XRD, and SEM-EDS were utilized to analyze the morphology, chemical components, and mineral phases. Pore size distribution and microstructural rearrangement were assessed using MIP and 29Si NMR. Additionally, TG-DTG analysis was conducted to analyze thermal stability. The results indicated that optimal additions of metakaolin and SiCw increased interactions among gel products and induced more chemical reactions, thus exhibiting better mechanical strength and thermal properties. The water absorption and permeable porosity were also improved. The inclusion of SiCw notably provided more nucleation sites and increased the dissolved aluminum content, enriching the phase in the system.

Ultrabroad electromagnetic absorbing core-shell SiC@SiO2 nanocomposites derived from in situ oxidation SiC whiskers

The amazing developing electromagnetic technology has brought severe challenges to the military and civilian fields, efficient electromagnetic wave absorption (EWA) materials with high-temperature resistance are urgent needed. In this paper, SiC@SiO2 nanocomposites with unique core-shell structures were successfully prepared using a straightforward method by in situ oxidation SiC whiskers. By regulating the sintering temperature and oxidation time, the microstructures and EWA performance of SiC@SiO2 nanocomposites were explored. The results show that the core-shell SiC@SiO2 nanocomposites obtained after sintering at 1200 ℃ for 0.5 h exhibits the best EWA performance, where the minimum reflection loss (RLmin) of −36.80 dB at the thickness of 2.68 mm and the effective absorption bandwidth (RL<-10 dB, EAB) of 9.85 GHz at a matching thickness of 4.24 mm. Specially, the EAB can reach up 10.98 GHz with the filling content of only 10%, which surpasses most SiC-based absorbers. The ultrabroad absorbing bandwidth can be attributed to that the unique core-shell structures of SiC whiskers with in-situ grown SiO2 layers on the surface provide good impedance matching, multiple reflection and scattering and interface polarization effects. This work provides a new strategy for the design of high temperature resistant absorbing materials.

SiC whisker toughened WC-Al2O3-ZrO2 binderless cemented carbides via fast-hot-pressed sintering and DFT calculations

Binderless cemented carbide has garnered attention for its exceptional hardness and suitability in extreme service conditions. The absence of a metal binder, however, leads to inadequate fracture toughness, which limits its broader application. This study explores the influence of SiC whisker on the microstructure and mechanical properties of WC-Al2O3-ZrO2 binderless cemented carbide, utilizing a combination of experimental method and Density Functional Theory (DFT) calculations. The inclusion of 1 wt% SiC whisker resulted in a notable increase in fracture toughness, reaching an impressive toughness of 16.4 ± 0.5 MPa⋅m1/2, while maintaining a high Vickers hardness of 19.4 GPa. DFT calculations provided insights into the interface energy, cohesive energy, and charge density differences at the WC/SiC interface. This work also presents two models depicting the behavior of whiskers during fracture, based on the observed microstructure and computational findings. Overall, the present work offers significant insights and practical guidance for advancing binderless cemented carbide technologies.

Hot-press sintering of SiC whisker reinforced TiB2-B4C composites and its mechanical property characterizations

TiB2-B4C composites modified by SiCW with excellent mechanical properties were prepared using hot-press sintering. The effects of SiCW content on the microstructure, densification behavior and mechanical properties were investigated. The dynamic failure behavior was analyzed through the Hopkinson Bar (SHPB) testing. The results demonstrate that the addition of SiCW can effectively refine the microstructure and simultaneously improve the mechanical properties. The TiB2-B4C composite renforced with 6 wt% SiCW exhibits a nearly full-dense microstructure and excellent mechanical properties. The relative density, flexural strength, Vickers hardness and fracture toughness can reach to 99.95 %, 724 ± 61 MPa, 19.8 ± 0.7 GPa and 6.7 ± 0.3 MPa m1/2, respectively. The dynamic failure behavior exhibits that the damage degree increases with elevated loading speed. Moreover, the single-peak and double-peak of the waveform correspond to the two damage degrees of "broken" and "crushed".

Microstructure and mechanical properties of high-pressure sintered B6O-SiC nanocomposites

Boron suboxide (B6O) is recognized as a superhard material with a low mass density, high resistance to chemical wear, and excellent wear resistance. Despite its desirable properties, the limited fracture toughness of B6O restricts its application in industrial contexts. This study presents the structural and mechanical characterization of B6O-SiC nanocomposites, which were synthesized via a high-pressure high-temperature sintering process of B6O powders and SiC whiskers. The sintering process induced fragmentation of SiC whiskers, resulting in the homogenous distribution of SiC fragments within the B6O matrix. An increase in SiC content was observed to decrease the composite's hardness, while initially reducing then enhancing its toughness. The nanocomposites containing 20 wt% and 30 wt% SiC whiskers exhibited significant improvements in fracture toughness, averaging 6.5 MPa m1/2 and 7.0 MPa m1/2, respectively—approximately threefold the toughness of polycrystalline B6O—while sustaining high hardness values of 36.3 GPa and 35.6 GPa on average. Microstructural analyses revealed that the composites’ superior mechanical performance is due to the presence of strong grain boundaries, as well as a high density of nanotwins and stacking faults. The findings demonstrate a viable method for producing B6O-based nanocomposites with enhanced hardness and toughness, potentially expanding their industrial applicability.

Toughened bulk high-entropy diborides with high hardness and enhanced oxidation resistance via SiC whiskers

The fracture toughness and oxidation resistance are crucial factors affecting the practical applications of high-entropy diboride ceramics (HEBs). In this study, silicon carbide whiskers (SiCw) were introduced as a reinforcement for HEBs for the first time. To achieve a uniform dispersion of SiCw within the HEB powders, a combination of simultaneous ultrasonic dispersion, mechanical agitation, and freeze-drying technology was employed. Consequently, a series of composites, (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2-nSiCw (n = 0–20 vol%), were densified by spark plasma sintering. The effect of SiCw on the microstructure and mechanical properties of the HEBs were studied, as well as the toughening mechanism involved. The results revealed that the introduction of SiCw led to grain-size refinement in (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2, along with significant improvements in relative density, hardness, fracture toughness, and oxidation resistance. The relative density, hardness and fracture-toughness of (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2-SiCw composites exhibited an initial increase followed by a decrease with increasing SiCw content. Specifically, the (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2–15 vol% SiCw composite simultaneously obtained the highest hardness of 25.6 GPa and fracture-toughness of 4.8 MPa·m1/2, representing a 26% improvement compared to (Hf0.2Zr0.2Ta0.2V0.2Nb0.2)B2 ceramics.

Silicon carbide whiskers reinforced silicon carbide ceramics prepared by vat photopolymerization and liquid silicon infiltration

The development of additive manufacturing technique provides possibility to prepare SiC ceramics with complex shapes. However, defect control in the debinding and sintering stages is still a great challenge for the vat photopolymerized components. Here, SiC ceramics were manufactured by vat photopolymerization followed by liquid silicon infiltration, using SiC whiskers as the reinforcement. In the debinding stage, the SiC whiskers prevented the propagation of micro-cracks that induced by the formation and emission of gaseous substance. Also, the SiC whiskers provided channels for the infiltration of liquid silicon during sintering, thus the bulk density of the as-sintered SiCw/RBSC composite reached 2.95 g/cm3 at the whiskers fraction of 8 wt%. Because of the various toughening mechanisms introduced by SiC whisker, the flexural strength and Vickers hardness of the composite increased up to 352.2 MPa and 17.54 GPa, respectively. Thus, this work provides a new strategy to control micro-defects in vat photopolymerized SiC ceramics.

Improving the comprehensive properties of ZrO2–C materials with aid of TiO2 addition

Owing to the harsh working condition, the ZrO2–C materials used in the slag line in the submerged entry nozzle are confronted with serious slag erosion. In order to solve this issue, different amounts of TiO2 addition ranging from 0 to 6 wt% are added and their effects on the erosion resistance of ZrO2–C materials in addition to phase composition, microstructure, physical properties and high-temperature mechanical properties are investigated in this work. When the sintering temperature is above 1400 °C, fine TiC grains and SiC whiskers are in-situ formed and distributed around ZrO2 particles, which can reinforce the matrix and improve the strength of ZrO2–C materials. With the amount of TiO2 addition increasing, the cold strength of ZrO2–C materials increases while the high-temperature strength slightly decreases. Combining with the erosion resistance, the optimum amount of TiO2 in ZrO2–C materials is determined to be 4 wt%, in which the cold compressive strength (46.13 MPa), the cold modulus of rupture (35.12 MPa) and the residual strength after thermal shock (15.01 MPa) reach the maximum. Based on this, the promotion mechanism of erosion resistance is further discussed with aid of molecular dynamics simulation.