SiC Whiskers Research Articles

Preparation and properties of mullite-SiC-O′-SiAlON composites for application in cement kiln

Mullite-SiC-O′-SiAlON composites were prepared using bauxite-based homogenized mullite, silicon powder and phenolic resin as raw materials. The phase composition, microstructure and properties of samples with various Si addition calcined at 1500 °C under reducing atmosphere were investigated. The results indicated that the mullite-SiC-O′-SiAlON composites were obtained at 1500 °C in carbon embedded condition by firing Si and bauxite-based mullite mixtures. The whisker-like SiC and O′-SiAlON in the composites were formed because of the reactions between Si and C, CO or N2, and the growth of whiskers followed VS and VLS mechanisms. Both cold and high temperature strength, and thermal shock resistance of the composites increased with increase of silicon powder addition, and the optimized Si addition was 10 wt%. The improved properties at high temperature were due to the non-oxide whiskers filling in the skeleton of mullite and forming interlocking network structure as well as direct bonding between SiC whiskers and mullite, creating strengthening and toughening effects.

Tensile properties and microstructure of ZK60/SiCw composite after extrusion and aging

In this study, high-temperature tensile properties and microstructure of ZK60/SiCw composite were investigated in “as-cast” and “extruded + precipitation-hardened” conditions. Stir casting followed by extrusion and aging at 175 °C for 12 h was employed to prepare the composite samples containing 5 vol% SiC whiskers. Aligned whiskers and the severely deformed matrix resulted in a quasi-continuous network structure of the reinforcement and laminar structure of the matrix. Tensile tests, conducted in the temperature range of 25–350 °C, revealed that the anisotropic structure led to an improvement in the ductility and strength. The elastic modulus of the composite was dependent on the alignment and distribution of the reinforcement. While the elastic modulus in the extrusion direction was close to the upper bound of the Halpin–Tsai (H-T) model at temperatures below 250 °C, it approached to the lower bound of the model at temperatures above 300 °C. Moreover, 0.2% proof stress, ultimate tensile strength and elastic modulus decreased nonlinearly with temperature. Examination of the fracture surfaces revealed the fracture of whiskers with slight pull-out due to the strong whisker/matrix interface.

Role of graphite nano-flakes on the characteristics of ZrB2-based composites reinforced with SiC whiskers

Spark plasma sintering technique was utilized to densify the hybrid ZrB2-based UHTCs co-toughened with SiC whiskers and different weights of graphite nano-flakes. The role of nano-graphite on the structure, hardness, densification, and toughness characteristics of ZrB2–SiCw–graphite nanocomposites were inspected. Although all UHTC matrix composites approached to full densification, a 100% dense ceramic was obtained by the incorporation of 5 wt% graphite nano-flakes. The grain coarsening phenomenon stopped significantly in the presence of carbonaceous nano-additive. Phase and microstructural investigations revealed that no in-situ phases were formed during the SPS consolidation, owing to the non-reactivity of ZrB2–SiCw–graphite system. The Vickers hardness dropped slightly from 22 to 19.5 GPa with increasing the nano-graphite content. However, the fracture toughness approached 6.2 MPa.m½ by the incorporation of 5 wt% graphite nano-flakes, remarkably tougher than that of graphitic-carbon-free ceramic with a toughness of 4.7 MPa·m½.

Thermal conductivity and mechanical properties of polyimide composites with mixed fillers of BN flakes and SiC@SiO2 whiskers

AbstractPolyimide (PI) composites with mixed fillers of BN flakes and SiC whiskers exhibit enhanced thermal conductivity and mechanical properties. In order to improve dispersion and interaction of these mixed fillers within the PI matrix, BN flakes were modified by a titanate coupling agent while SiC whiskers were oxidized at 750°C for 60 minutes to produce SiC@SiO2 followed by silane coupling agent modification. PI composites reached a maximum thermal conductivity of 0.95 W/m K at volume fraction of mixed fillers of 27.6 vol% when the weight ratio of BN flakes to SiC@SiO2 whiskers was 1:4. The enhanced thermal conductivity is likely attributed to the formation of heat conductive networks constructed by BN flakes and SiC@SiO2 whiskers and the improved interfacial affinity between fillers and matrix. The optimized Nielsen‐mold confirms the distribution and morphology of fillers affect the thermal conductivity of PI composites. In addition, SiC whiskers enhanced the mechanical property of PI composites and the influence of fillers on the mechanical property was further elaborated.

Fabrication and characterization of SiC whiskers toughened Al2O3 paste for stereolithography 3D printing applications

To prevent the agglomeration of silicon carbide whiskers (SiCw) in photosensitive ceramic paste, a butanone-ethanol azeotropic solvent is employed to facilitate the dispersion of alumina particles, SiC whiskers and UV resins. Moreover, SiCw/Al2O3 ceramic pastes, with 5–15 vol % SiCw, are prepared by using ball milling, stirring and distillation processes. The mixture of butanone-ethanol solvent and resins can be effectively separated at 70 °C without weakening the polymerization of UV resin. Moreover, an empirical equation is established to evaluate the relationship between SiCw content, aspect ratio and viscosity of resulting ceramic paste. The 15 vol % SiCw/Al2O3 composite ceramic, with SiCw aspect ratio of 50, renders higher resistance to liquid flow and results in a high viscosity of 30,000 mPa s at the shear rate of 30 s−1. Furthermore, a modified equation is established to predicate the curing depth of ceramic pastes with different amounts of SiCw, where 15 vol % SiCw/Al2O3 composite results in higher light scattering properties, leading to lowest Cd of ∼0.061 mm. Finally, the complex-shaped SiCw/Al2O3 ceramic component, prepared by SL 3D printing technology, debinding and sintering processes, exhibited a superior fracture toughness of 7.1 ± 1.20 MPa m1/2 and a higher hardness of 17.6 ± 0.78 GPa.

Synthesis of SiC whiskers via catalytic reaction method in self-bonded SiC composites

Catalyzed by in-situ formed Fe nanoparticles (NPs), 3C–SiC whiskers were prepared from expanded graphite and Si powders after firing at 1573 K for 3 h in Argon. The density functional theory calculations revealed that Fe catalysts facilitated the formation of SiC nucleus and the epitaxial growth of SiC whiskers via reducing the bonding strength in CC dimer as well as Si–O and C–O bonds. Moreover, using SiC, expanded graphite and silicon powders as starting materials Fe-catalyzed self-bonded SiC composites were fabricated. Lots of SiC whiskers were synthesized in the as-prepared composites, leading to remarkable enhancements in high temperature mechanical behavior, oxidation resistance and cryolite resistance of the self-bonded SiC composites.

SiC whiskers: A strategy to modify the high-temperature performance of laminated ZrB2–SiC ceramics

With SiC whisker and SiC particle as interface layers, ZrB2–SiC–SiCw (LZ-Sw) and ZrB2–SiC–SiCp (LZ-Sp) laminated ceramics were prepared by tape casting and hot pressing. Fracture behaviors and accompanying microstructural changes were studied in the range from 20 to 1500 °C. At 20 °C, both LZ-Sw and LZ-Sp exhibited excellent flexural strengths in parallel direction of 607 ± 58 and 568 ± 46 MPa, respectively. From 20 to 1500 °C, the flexural strength of LZ-Sw was always higher than that of LZ-Sp. From 1200 to 1500 °C, the flexural strength of LZ-Sw declined relatively slowly while that of LZ-Sp dropped sharply. At 1500 °C, the flexural strength of LZ-Sw reached 361 MPa in the parallel direction, 66.4% higher than that of LZ-Sp (217 MPa). The superior high-temperature performance of LZ-Sw was caused by porous interface layers composed of SiC whiskers and ZrB2 particles, which reduced the enrichment of the glassy phase and avoided grain-boundary sliding.

Effect of SiC nanoparticles on in-situ synthesis of SiC whiskers in corundum–mullite–SiC composites obtained by carbothermal reduction

Corundum–mullite–SiC composites were synthesised using a carbothermal reduction method. The effects of SiC nanoparticles and sintering temperatures on the phase transformation of the composites and the synthesis of SiC whiskers were studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Results indicated that corundum, mullite, and SiC whiskers were produced as final products at 1600–1650 °C. SiC whiskers were formed through the vapor–solid mechanism. The added SiC nanoparticles worked as nucleating agents to facilitate the carbothermal reduction of aluminosilicates and formation of SiC whiskers. The sample with the added SiC nanoparticles exhibited a high yield of β-SiC of 17.1%. Furthermore, the SiC nanoparticles decreased the formation temperature of SiC whiskers from the original 1600 °C to 1500 °C, and the porosity of the composites was increased from 56.7% to 64.7% by increasing the partial pressure of SiO gas. This study provides an insight into the more efficient synthesis of composites with SiC whiskers through the carbothermal reduction of aluminosilicates.

Effect of SiCw volume fraction and cold pressure on microstructure and mechanical properties of aluminum matrix composites

The alloy powder and SiCw reinforcement were ball milled, cold-pressed, sintered, hot extruded and solution aged to obtain excellent mechanical properties such as hardness and compressive strength. The microstructure and properties of the material were characterized by metallographic microscope, scanning electron microscope (SEM), EDS, x-ray diffraction (XRD), HV-1000 microhardness and 7051 eddy current conductivity. The results show that the distribution of SiC whiskers in the mixed powder is relatively uniform, but there is still a small amount of agglomeration phenomenon in the sintered sample. The optimum cold pressure is 740 MPa. With the increase in SiCw content, the hardness, dislocation density and compressive strength of aluminum matrix composites are improved. The compressive strength of 5% SiCw reinforced aluminum matrix composite is 658.9 MPa and the elongation is 13.9%.

Electrical conductivity anisotropy of copper matrix composites reinforced with SiC whiskers

Abstract Copper matrix composites reinforced with 1, 3, 5, 7 vol.% Cu-coated SiC whiskers of consistent orientation (SiCw/Cu) were prepared by powder metallurgy and hot extrusion. The microstructure of composites was investigated by scanning electron microscopy. The SiC whiskers were arranged along the direction of hot extrusion and distributed uniformly. The composites were fabricated into specimens with different whisker orientations, and their electrical conductivity was tested. The effects of SiC whiskers orientation and content on the electrical conductivity of composites were investigated through experiment. Results show that the SiC whiskers content was the major factor affecting the electrical conductivity of the composites. With increasing SiC whisker orientations angel, the electrical conductivity of composites is improved. The electrical conductivity model has been established by taking into account the SiC whiskers content, whisker orientation and microstructure parameters, and the results were in good agreement with experimental data. Graphical abstract: Copper matrix composites reinforced with SiC whiskers of consistent orientation were prepared. The orientation of SiC whiskers changes from 0∘ to 90∘, resulting in electrical conductivity anisotropy of composites.

Influence of novel sintering process on the densification and microstructures of ceramic composite materials

Generally, a fully dense ceramic material must be fabricated at very high temperature or pressure even by the hot pressing process. In this study, a novel hot pressing process was proposed in order to improve the densification and hardness of ceramic tool materials. Synthetic graphite powder was used in the novel process to replace graphite paper as a lining material. The sintering temperature of SiC whisker toughened ceramic materials can be lowered by 150 °C. The experimental trials showed that the relative density and Vickers hardness of the ceramic materials were remarkably improved. The greatest improvement was 23.78% in Vickers hardness increasing from 18.00 ± 0.60 GPa to 22.28 ± 0.38 GPa. The homogeneous and densified microstructures were obtained because of the good air permeability of synthetic graphite powder. At the end of the sintering process, the synthetic graphite powder was still in the powder form and was easy to remove from the sintered body. The novel process can solve the problem of densification of the difficult-to-sinter ceramic materials, providing an effective solution in preparing high-density ceramic tools.

A simple and clean method to prepare SiC-containing vitreous ceramics for solar thermal storage in the clay-feldspar system

A simple and clean in-situ method was designed to prepare SiC whisker-reinforced vitreous ceramics for solar thermal storage. SiC whiskers were in-situ synthesized in the clay-feldspar system via a carbon-buried sintering process to improve the thermal properties of vitreous ceramics. The synthesis mechanism and the optimized processing procedure of SiC-containing vitreous ceramics from the clay-feldspar system were obtained. Results indicated that the in-situ SiC whiskers were synthesized inside the pores of vitreous ceramic matrix through the vapor-solid mechanism and covered by the liquid of K2O–Al2O3–SiO2 system. SiC whiskers with a diameter of 9–23 nm decreased the thermal expansion coefficients of the vitreous ceramics significantly from 6.59 × 10−6 °C−1 to 4.23 × 10−6 °C−1 (room temperature∼1000 °C). Meanwhile, the thermal conductivity increases to 4.78 W·(m·k)−1, 2.6 times higher than that of the original products. The increased porosity was found to improve the amount of SiC whiskers by providing space for their growth. SiC whiskers also enhanced the mechanical properties of the products and the sample with the largest content of SiC exhibited the highest bending strength of 75.7 MPa. The introduction of SiC whiskers through the in-situ synthesis method makes vitreous ceramics more competent for solar thermal storage applications. The in-situ method can save the energy and costs needed for separately producing SiC whiskers and prevent the inhalation toxicity of SiC whiskers.

3D-SiC decorated with SiC whiskers: Chemical vapor infiltration on the porous 3D-SiC lattices derived from polycarbosilane-based suspensions

SiCw/3D-SiC composites were fabricated by chemical vapor infiltration (CVI) of the 3D SiC lattices, which were prepared via direct ink writing of polycarbosilane-based suspensions. Microstructure, composition and tensile strength of the composites were investigated. Curing and pyrolysis temperature greatly affected the shrinkage, weight loss, density and composition of the 3D SiC. Although sound structure with spanning feature was achieved, cracks and pores in 3D SiC were formed during the pyrolysis owing to the large shrinkage. CVI process decreased the porosity and led to fully dense surface of the SiCw/3D-SiC composites. After 60h of CVI, short β-SiC fibres or long SiC whiskers were deposited in the structural spacing of 3D lattices or spherical pores inside the filaments, respectively. The tensile strength of the composites by CVI increased from 3.3 MPa to 15.7 MPa (20 h) and 47.3 MPa (60 h), due to the high strength of dense CVI layers and in-situ formed SiC whiskers in pores. This work showed a way to strengthen the 3D SiC with in-situ formed whiskers via the polymer precursor routes.

Microstructure and mechanical property of SiC whisker coating modified C/C composite/Ti2AlNb alloy dissimilar joints prepared by transient liquid phase diffusion bonding

SiC whisker coating was prepared on the surface of C/C composite successfully by CVD, and transient liquid phase (TLP) diffusion bonding was employed to realize the joining of SiC whisker coating modified C/C composite and Ti2AlNb alloy using Ti–Ni–Nb foils as interlayer. The microstructure, shear strength and fracture behavior were investigated by scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD) and universal testing machine. The results show that SiC has good compatibility with C/C composite, and gradient interface formed between SiC-modified C/C composite and Ti2AlNb alloy. When the bonding experiment was carried out under bonding temperature of 1040 °C and holding time of 30min with 5 MPa pressure in vacuum, the joints formed well and no obvious defects can be observed. The typical microstructure of joints is C/C composite/SiC + TiC/Ti–Ni compounds + Ti–Ni–Nb solid solutions/residual Nb/diffusion reaction layer/Ti2AlNb alloy. With the increasing of bonding temperature, the thickness of joining area increased due to sufficient element diffusion. However, when bonding temperature is elevated to 1060 °C, some defects such as cracks and slag inclusions exist in the interface layer between interlayer and Ti2AlNb. The joints with maximum average shear strength of 32.06 MPa are bonded at 1040 °C for 30min. C, SiC and TiC can be found on the fracture surface of joints bonded at 1040 °C which indicated that fracture occurred at the interface layer adjacent SiC layer.

The Influence of SiC and Al2O3 Whiskers on the Properties of Whisker-Reinforced cBN-Based Composites

Three types of cBN-based composites with TaN binder—without whiskers, with Al2O3 whiskers, and with SiC whiskers—have been produced by the high pressure-high temperature (HPHT) sintering. Density, hardness, Poisson ratio, and fracture toughness of the composites have been studied. The whisker-reinforced cBN-based composites exhibit a higher level of mechanical properties (hardness, fracture toughness) in comparison with the non-reinforced materials.

Microstructure, properties, and application of low carbon Al2O3‐C refractories used as submerged entry nozzles

AbstractWith the aim to achieve the application of low carbon Al2O3‐C refractory as submerged entry nozzle (SEN) materials, a comprehensive study on the microstructure, thermo‐mechanical properties, as well as application performance during use in the continuous casting was carried out by comparing with the traditional one. Both hot and cold modulus of ruptures of the low carbon Al2O3‐C refractory were superior to the traditional one, and its thermal shock resistance still kept in an acceptable level. The increase in the amount of SiC whiskers and the enhancement in the sintering are considered as the strengthening mechanism. In the industrial trial, the rapid loss of graphite caused by the large level fluctuation made the traditional Al2O3‐C refractory more susceptible to flux corrosion. For the low carbon Al2O3‐C refractory, however, the dense structure and the adhesion of viscous slag layer suppressed the slag penetration. Besides, the remaining SiC phases were also difficult to be wetted and dissolved by the flux. As a consequence, a better corrosion resistance was obtained, achieving a decrease of 27.6% in the average depth of the corrosion groove after working for 8 hous.

Construction of MnO nanoparticles anchored on SiC whiskers for superior electromagnetic wave absorption

MnO nanoparticles (MnONP) decorated SiC whiskers (SiCw) with superior electromagnetic (EM) wave absorption performances were successfully synthesized by combining a hydrothermal and thermal annealing process. The microstructural feature and the content of MnONP of these MnONP/SiCw composites could be effectively controlled by the hydrothermal temperature, resulting in the adjustable EM wave absorption capacity. Compared with the poor EM wave absorption property of pristine SiCw (−10.48 dB), the MnONP/SiCw heterostructures achieve substantially enhanced microwave absorption performances, attributing to the suitable impedance matching and improved loss ability arose from the synergetic effect between MnO and SiC, whose minimum reflection loss (RLmin) is improved to −15.84 dB for MnONP/SiCw obtained at 80 °C (S-80), to −15.17 dB for MnONP/SiCw obtained at 100 °C (S-100), and to −55.10 dB for MnONP/SiCw obtained at 120 °C (S-120), respectively. The MnONP/SiCw composite not only exhibits enhanced microwave absorption property, but also presents wider effective absorption bandwidth (EAB), reaching up to 5.4 GHz for S-80, 3.6 GHz for S-100 and 5.2 GHz for S-120 in comparison with pristine SiC (1.5 GHz). This work is expected to provide an effective approach to enhance EM wave absorption property of dielectric materials by incorporation of MnO and the MnONP/SiCw composites could be as a promising candidate for EM wave absorption applications.

Fabrication and characterization of a mullite-foamed ceramic reinforced by in-situ SiC whiskers

In this study, a new mullite-foamed ceramic, reinforced with in-situ SiC whiskers (MCS) and applied as the insulating lining of thermal equipment used in cement production, was investigated. Compared with a conventional mullite-foamed ceramic (MC), the MCS phase composition, microstructure, compressive strength, thermal conductivity and alkali corrosion resistance were investigated by using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Factsage® software. The results showed that after being fired in granular coke, the SiC whiskers formed into MCS struts and were distributed in the pores between the interconnected needle-like mullite. Although the formation of SiC with higher conduction slightly increased MCS thermal conductivity, it significantly enhanced the compressive strength and alkali corrosion resistance of the foamed ceramic. Compared with the MC, although the MCS had higher bulk density (3.9%), and higher thermal conductivity (9.5% at 800 °C), it was more important that greatly improved compressive strength (by 60%) and better alkali corrosion resistance was achieved.

Investigation of Electrodeposition External Conditions on Morphology and Texture of Ni/SiCw Composite Coatings

Recently, a strategy of synthesizing SiC whisker-reinforced nickel (Ni/SiCw) composites with excellent mechanical properties by electrodeposition has been proposed for exploring its potential applications in micromechanical devices. In this paper, a series of external conditions that affected the content of SiC whiskers in composite films were studied, such as cathode current density, stirring rate and electrolyte temperature. The experimental results indicated that the optimum morphology was obtained at a stirring speed of 300 rpm, a temperature of 50 °C, and a current density of 18 mA/cm2. Additionally, the content of SiC whiskers and textural preference were also investigated by varying its external conditions, and the results demonstrated that the composites with high mass percentage whiskers are more advantageous for electrocrystallization of Ni in the (200) orientation. Finally, the relationship between external conditions and intrinsic morphology, composition and texture of Ni/SiCw composites was revealed, and it provides a constructive approach to fabricate the high-content SiC whiskers of these composites.

3D SiC containing uniformly dispersed, aligned SiC whiskers: Printability, microstructure and mechanical properties

3D SiC-based lattices with aligned SiC whiskers were prepared via direct ink writing of SiCw/polycarbosilane (PCS)-based suspensions. Suspensions with different solid loading were prepared and used to investigate the morphology and printability of 3D SiCw/SiC lattices. Filaments with the morphologies of accumulation, coiling, meandering and straight were achieved with different printing height and speed. Higher printing height favored the formation of coiled filaments with longer periodic structure and increased amplitude. 3D lattices with straight filaments and good retention of shape were achieved only when applying a suitable printing parameters for SiCw/PCS-based suspensions with a solid loading of 62.3 vol%. The resulted 3D lattices with the porosity around 62% showed impressive bending and compression strength of 33.2 ± 5.2 MPa and 30.6 ± 4.3 MPa, respectively. The satisfactory properties of 3D SiCw/SiC lattices were contributed by the pullout of the aligned SiC whiskers. Furthermore, this 3D technique via the Polymer-derived Ceramics (PDCs) route allows the fabrication of large sized samples, which opens new opportunities for the fabrication of 3D structures with unique mechanical and functional properties in practical dimensions.