SiC Composite Powders Research Articles

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.

Microstructure and properties of molybdenum composite coatings by plasma spraying of Mo–SiC and MoO3–Al–SiC composite powders

To improve the sliding wear resistance of plasma sprayed Mo coating, Mo–SiC and MoO3–Al–SiC composite powders were used to prepare Mo composite coatings by plasma spraying. The results show that the introduction of SiC improved the mechanical properties and sliding wear resistance of plasma sprayed Mo coating. The reactivity of Mo and SiC was low during plasma spraying Mo–SiC composite powder. The thermite reaction for MoO3 and Al was not conducive to the densification of the composite coating prepared by MoO3–Al–SiC composite powder, but improved the reactivity of in-situ generated Mo and SiC, and the Nowotny phase Mo4.8Si3C0.6 was observed in the coating. The coating prepared by Mo–SiC composite powder displayed better mechanical properties and sliding wear resistance than that of the coating prepared by plasma spraying MoO3–Al–SiC composite powder. The coating obtained by Mo–SiC composite powder revealed a combination of adhesive wear, abrasive wear and oxidation wear.

Application of SiO2-coated SiC powder in stereolithography and sintering densification of SiC ceramic composites

Stereolithography additive manufacturing of SiC ceramic composites has received much attention. However, the forming efficiency and mechanical properties of their products need to be improved. This study aimed to prepare SiC ceramic composites with complex shapes and high flexural strength using a combination of digital light processing (DLP) and reactive solution infiltration process (RMI). A low-absorbance SiO2 cladding layer was formed on the surface of SiC powder through a non-homogeneous precipitation process. With the densification of the cladding layer at high temperatures, SiO2-coated SiC composite powder was used to formulate a photosensitive ceramic slurry with a solid content of 44 vol%. The resulting slurry exhibited a considerable improvement in curing thickness and rate and was used to mold ceramic green body with a single-layer slicing thickness of 100 μm using DLP. The ceramic blanks were then sintered and densified using a carbon thermal reduction combined with liquid silica infiltration (LSI) process, resulting in SiC ceramic composites with a density of 2.87 g/cm3 and an average flexural strength of 267.52 ± 2.5 MPa. Therefore, the proposed approach can reduce the manufacturing cycle and cost of SiC ceramic composites.

TEM characterization and reaction mechanism of composite coating fabricated by plasma spraying Nb–SiC composite powder

Niobium carbide composite coatings with Nb2C, NbC, Nb3Si as the main phases were prepared in situ on the surface of TC4 titanium alloy by plasma spraying Nb–SiC composite powder. The microstructure of the coating was characterized in detail by TEM, and the reaction mechanism of Nb–SiC was revealed. Sub-micron and nano-scale NbC grains dispersed in Nb3Si region, nano-Nb/Nb3Si cellular eutectic region, and equiaxed Nb2C nanograins region were formed in the coating. The research results show that Nb and SiC reacted firstly to form cubic NbC and Nb3Si phases during the plasma spraying process. Then, NbC with a higher melting point took the lead in crystallization during the cooling process of the coating, forming sub-micron and nano-scale NbC granular fine grains. Nb3Si with a lower melting point crystallized around the sub-micron and nano-scale NbC granular fine grains in the subsequent cooling process. In the plasma spraying process, the molten droplets formed Nb/Nb3Si cellular eutectic structure under large temperature gradient and extremely fast cooling rate. The remaining Nb in the raw material powder formed a diffusion couple with NbC to generate fine and dispersed nano-equiaxed Nb2C with cubic structure. The present investigation provides a reference for the reaction synthesis of advanced nanocomposites using Nb–SiC system.

Plasma sprayed TiC–Ti5Si3–Ti3SiC2–SiC composite coatings using annealed Ti–SiC composite powders based on SiC content

The TiC–Ti5Si3–Ti3SiC2–SiC ceramic composite coatings were prepared with in-situ reaction by plasma spraying annealed Ti–SiC–C composite powders. The effect of SiC content in the annealed composite powders at 1200 °C on the microstructure and properties of the coatings was studied. With the increase of SiC content, the phases in the annealed Ti–SiC composite powders changed from Ti, SiC, TiC and Ti5Si3 to SiC, TiC, Ti5Si3 and Ti3SiC2. The phases of the sprayed coatings were mainly composed of TiC, Ti5Si3, Ti3SiC2 and a small amount of residual Si, and their content were closely related to SiC. The coating hardness first increased and then decreased, while their mass loss showed an opposite trend to that of hardness. The T1SCC (molar ratio of Ti-SiC-C is 3:1:1) coating had the highest hardness of HV 1509 and the lowest mass loss of 0.0019 g, whereas its fracture toughness was 3.51 MPa m−2.

Microstructure, formation mechanism and properties of plasma-sprayed Cr7C3—CrSi2—Al2O3 coatings

The Cr7C3—CrSi2—Al2O3 composite coatings were prepared by plasma spraying Cr7C3—CrSi2—Al2O3 and Al—Cr2O3—SiC composite powders, respectively. The microstructure, formation mechanism and properties of the two Cr7C3—CrSi2—Al2O3 composite coatings obtained by plasma spraying were investigated, and the reaction mechanism of the Al—Cr2O3—SiC system was explored. The results show that the coating obtained by plasma spraying Al—Cr2O3—SiC composite powders had thinner lamella and more tortuous interlayer interface, and the in-situ synthesized Cr7C3, CrSi2 and Al2O3 in the coating were all nano-crystallines. Compared with the Cr7C3—CrSi2—Al2O3 coating prepared by plasma spraying Cr7C3—CrSi2—Al2O3 composite powders, the plasma-sprayed Cr7C3—CrSi2—Al2O3 coating obtained from Al—Cr2O3—SiC composite powders had higher density, higher microhardness (increased by 20%), better fracture toughness and lower wear rate (reduced by 28%).

In situ synthesis of Al2O3–SiC powders via molten-salt-assisted aluminum/carbothermal reduction method

Al 2 O 3 –SiC composite powder (ASCP) was successfully synthesized using a novel molten-salt-assisted aluminum/carbothermal reduction (MS-ACTR) method with silica fume, aluminum powder, and carbon black as raw materials; NaCl–KCl was used as the molten salt medium. The effects of the synthesis temperature and salt-reactant ratio on the phase composition and microstructure were investigated. The results showed that the Al 2 O 3 –SiC content increased with an increase in molten salt temperature, and the salt–reactant ratio in the range of 1.5:1–2.5:1 had an impact on the fabrication of ASCP. The optimum condition for synthesizing ASCP from NaCl–KCl molten salt consisted of maintaining the temperature at 1573 K for 4 h. The chemical reaction thermodynamics and growth mechanism indicate that the molten salt plays an important role in the formation of SiC whiskers by following the vapor-solid growth mode in the MS-ACTR treatment. This study demonstrates that the addition of molten salt as a reaction medium is a promising approach for synthesizing high-melting-point composite powders at low temperatures.

Anisotropic binary TiB2–SiC composite powders: Synthesis and microwave absorption properties

Microstructure control and multiple compounding methods in the synthesis stage can enhance microwave absorption performance of microwave absorbents. In this work, we successfully synthesized binary TiB2–SiC (TsBC) powders with hexagonal sheet (TiB2) and particle (SiC) interlocking structures by sol-gel carbothermal reduction method. We investigated the effect of raw material ratio and synthesis temperature on the synthesized powders and evaluated the microwave absorption properties of the synthesized TsBC powders. It was found that the TsBC absorber exhibited excellent microwave adsorption properties with the minimum Reflection Loss (RL) reached −21.8 dB at 17.4 GHz corresponding to the thickness of 4 mm. This excellent performance was attributed to the interfacial polarization between TiB2–SiC interfaces and the multiple reflections between the sheet-particle interlocking structures.

Influence of pre-synthesized Al2O3–SiC composite powder from clay on properties of low-carbon MgO–C refractories

Influence of pre-synthesized Al2O3–SiC composite powder from clay on properties of low-carbon MgO–C refractories

Impact of the SiC addition on the morphological, structural and mechanical properties of Cu-SiC composite powders prepared by high energy milling

The effect of the SiC content on the microstructural, mechanical, and magnetic properties of Cu(1 − x)SiC(x) composite powders (x = 0, 2, 10 and 15 wt%) prepared by high energy milling for 30 h was investigated. The results showed that Cu particles were severely deformed and formed plate like particles of different sizes, while SiC particles were fragmented and embedded in the Cu phase, thus, forming composite particles. As the SiC content increased, the average particle size decreased from 40.75 to 12.84 µm. Besides, XRD data showed a decrease in the crystallite sizes of the Cu phase (from 23.66 to 21.56 nm), accompanied by an increase in the lattice micro-strain (from 0.41 to 0.46%). Changes in the lattice parameters of the Cu phase were observed. The Vickers microhardness were measured in compacted powder samples and reached a maximum value of 135.22 HV for the sample with 15 wt% SiC. The samples showed hysteresis magnetic behavior at 300 K, and with a maximum saturation magnetization of 0.123 emu/g. The weak magnetic signal is mainly due to Co impurities present in the WC from the milling media.

Improving the sinterability of ZrC–SiC composite powders by Mg addition

High-density ZrC–SiC composite ceramics are typically sintered under demanding conditions, specifically, high sintering pressures and high temperatures. However, the need for such conditions can be alleviated by the use of ZrC–SiC composite nanoparticles with a high sintering activity. In the present study, core-shell-structured hybrid ZrC–SiC composite nanoparticles were synthesised with the addition of Mg by using a sol-gel process combined with in-situ carbothermal reduction reactions. The synthesis route, characterisation, and sintering mechanism were investigated in detail. It was found that the addition of MgCl2 to the precursors of ZrC–SiC can not only strengthen the network structure of ZrC–SiC gel but also lead to the formation of an amorphous Mg–Si–O oxide coating on the nanoparticle surfaces, which enhances the sinterability of ZrC–SiC nanoparticles. As a result, a compact ZrC–SiC composite ceramic with a higher relative density (up to 91.3%) than the contrast sample was successfully prepared by pressure-free sintering at 1700 °C.

Production and Oxidation Resistance of HfB2–30 vol % SiC Composite Powders Modified with Y3Al5O12

The HfB2–30 vol % SiC composite powders modified with a small (2 and 5 vol %) amount of Y3Al5O12 were synthesized by the sol–gel method. Such a modification in producing an ultra-high-temperature ceramic of the corresponding composition optimized the process temperature and increased the oxidation resistance of the ceramic by stabilizing the formed hafnium dioxide in the cubic or tetragonal form. It was determined that the introduced X-ray amorphous phase Y3Al5O12 was distributed as a thin film on particles of hafnium diboride and silicon carbide and led to agglomeration of the latter; no formation of individual Y3Al5O12 particles was observed. Investigation of the thermal behavior of the obtained composite powders in an air flow in the temperature range 20–1200°C showed that the introduction of 5 vol % Y3Al5O12 virtually completely neutralized the effect of the initial surface oxidation of HfB2 in the temperature range 700–800°C, shifted the temperature of the beginning of oxidation and the maximum of the corresponding thermal event from 756 to 808°C, and decreased the intensity of this thermal event.

Volume combustion synthesis of B4C–SiC nanocomposites in tubular and spark plasma furnaces

The nano-sized B4C–SiC composite powders were in-situ synthesized with high purity in a short time at low temperatures. In this study, the mechanically activated mixtures of C, B2O3, Mg, and Si were used as raw materials. The synthesis processes were performed in tubular and spark plasma furnaces. The synthesized nanocomposites were acid, being leached to remove the MgO byproducts. The purity of the acid leached composites was determined through the XRD, EDS, and FTIR analyses. The purity level of the nanocomposites, which were synthesized in spark plasma furnace, was 90%, which was increased to 98% by using higher amounts of raw materials. Moreover, the average crystallite size of B4C and SiC were 17 and 41 nm, respectively, in the high-purity nanocomposite. The SEM and TEM investigations confirmed the synthesis of nano-sized B4C–SiC nanocomposites.

Microstructures evolution, formation mechanisms and properties of Sicp/ Al composite coatings on Ti-6Al-4v substrate via mechanical alloying method

In this present work, high-energy mechanical alloying method was successfully applied to fabricated Al-SiC coatings, which possessed a composite structure. The coatings fabricated by different Al-SiC weight ratio were studied. The results of scanning electron microscope(SEM) and Energy Dispersive X-ray spectrometer(EDS) revealed the microstructures and phase compositions of as-synthesized coatings, respectively. To test the mechanical properties of coated samples prepared at different Al content, the tests of microhardness value were carried out from the outermost coating to the inner substrate. Then, the effect of milling duration on coatings was also studied. Adhesion behaviors of the coatings at different milling time were investigated through scratch tests. And friction and wear resistance were also tested. Which further confirmed the surface strengthening effect of the coating. The formation mechanisms of the Al–SiC composite coating and Al–SiC composite powder were elaborated. Overall consideration of microstructure, phase composition and mechanical properties, the coating prepared with Al–SiC raw powder ratio of 65:35 at 7 h milling time was the optimal processing parameters on fabrication of Al–SiC composite coating. The Al–SiC coating shows high performance in adhesion behaviors and wear resistance, this method is capable to be applied to fabricate coatings on the inner walls of tubular specimens .

Effect of carbon source on the synthesis of ZrB2–SiC composite powders

This study is aimed to synthesize ZrB2–SiC composite powders by boro-carbothermal reduction of zircon using two different carbon sources, namely expanded graphite and carbon black. The effect of carbon sources on the phase composition and microstructure of composite powders was studied using an X-ray diffractometer, a scanning electron microscope, and an energy spectrum analyzer. Pure-phase ZrB2–SiC composite powders were prepared in 2 h at 1550 and 1500 °C 1500 °C using expanded graphite and carbon black, respectively. In the former case, anisotropic ZrB2–SiC composite powders were synthesized. Their ZrB2phase grains had an average diameter of 2.0 μm and regular hexagonal shape, while SiC phase grains were whisker-shaped, had an average diameter of 0.15 μm and aspect ratio exceeding 20. For carbon black, finer ZrB2grains and shorter rod-shaped SiC grains were obtained.

Production parameters affecting the synthesis and properties of hBN-SiC composites

In this study, the hexagonal boron nitride (hBN)-SiC composite powder synthesis was investigated with an in situ reaction method. Boric acid (H3BO3) and urea (CO(NH2)2) were used for hBN formation. In the hBN-SiC composite powder synthesis, primarily raw materials were homogeneously stirred in ethanol with Si3N4 balls. The samples were calcined and sintered by spark plasma sintering at 2000 °C under pressure of 50 MPa for 15 min. The characterization of composite samples was carried out by XRD, SEM-EDS, FTIR, and TG-DTA. The bulk density, Vickers hardness, and Young’s modulus of samples were also measured. Composites were obtained, which had homogeneous microstructure. Residual boron oxides were found in samples with short calcination times. Moreover, it was found that the production parameters affect the physical properties of the composites and the amount of the hBN in sintered samples.

The effect of sol-gel process on the microstructure and particle size of ZrC–SiC composite powders

ZrC–SiC composite powders were successfully synthesized by the combination of sol-gel technology and carbothermal reduction. The characterization of these powders was conducted by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effects of the important parameters of sol-gel process including the desiccant method, timing of introducing carbon source and heating-drying temperature on the final ZrC–SiC particle size and its distribution range were studied in details, and the mechanism of ZrC–SiC particles agglomeration and coalescence was also explored. The results show that the mean particle size increases with the heating-drying temperature rising, but introducing carbon source before gelation together with a freeze-drying treatment can produce the ultrafine ZrC–SiC composite powders having a minimum particle median diameter of 0.174 μm and the narrowest size distribution range.

Effects of particle size of raw materials on the characteristics of TiB2–SiC composites fabricated from B4C, TiC and Si powders

We studied the effects of particle size of raw materials (B4C, TiC and Si powders) on the characteristics of both TiB2–SiC composite powders and ceramics. Results show that the size of B4C and Si particles hardly affects the size of TiB2 and SiC particles because B4C is decomposed and consumed during the formation of TiB2, and Si is melted during the formation of SiC. The size of SiC particles is within the nano and submicron scale. However, the size of TiC particles determines the sizes of TiB2 particles and TiB2 grains in the composite ceramics because TiC particles serve as templates to form TiB2 particles. Consequently, the microstructure and mechanical properties of the TiB2–SiC composite ceramics are affected. The TiB2–SiC composites fabricated using nano-sized TiC powder possess smaller grain size, better dispersibility and more reasonable crack propagation path, thereby obtaining the optimal mechanical properties (Vickers hardness of 30.2 GPa, flexural strength of 732 MPa and fracture toughness of 7.37 MPa m1/2).

Laser additive manufacturing and homogeneous densification of complicated shape SiC ceramic parts

To improve the density of SiC ceramic components with complicated shape built by laser sintering (LS), cold isostatic pressing (CIP) and reaction sintering (RS) were incorporated into the process. In the process of LS/CIP/RS, Phenol formaldehyde resin (PF)-SiC composite powder was prepared by mechanical mixing and cold coating methods, with an optimized content of PF at 18 wt%. For the purpose of obtaining improved density of the sintered body after final reaction sintering, carbon black was added into the initial mixed powder. The material preparation, LS forming and densification steps were optimized throughout the whole fabrication process. The final sintered SiC bodies with the bending strength of 292 ~ 348 MPa and the density of 2.94–2.98 g cm− 3 were prepared using the PF coated SiC-C composite powder and the LS / CIP / RS process. The study further showed a positive and practical approach to fabricate SiC ceramic parts with complicated shape using additive manufacturing technology.

Preparation of Al<sub>2</sub>O<sub>3</sub>-SiC Composite Powder by Carbothermal Reduction of Coal Gangue and its Influence on Properties of Blast Furnace Stemming

Al2O3-SiC composite powders are prepared by carbothermal reduction method using coal gangue as raw material and carbonaceous materials (such as coke, anthracite, and carbon black) as reducing agents. The optimum conditions are as follows: when the addition of coke or anthracite is 50%, the temperature is at 1600 °C for 5 h, and adding 50% carbon black’s best temperature is at 1600 °C for 4 h. Based on the formula of stemming used in an iron and steel factory, Al2O3-SiC-C series blast furnace stemming refractory was prepared by adding Al2O3-SiC composite powder. The results show that the addition of Al2O3-SiC composite powders has a positive influence on the apparent porosity, volume density, and bending strength of the refractory. The effect of the amount of Al2O3-SiC composite powder on the slag corrosion resistance of the blast furnace stemming refractory was also studied by the static crucible method.