Photoluminescence of Nanometer SiC Powder

Photoluminescence of nanometer SiC powder was found firstly. By TEM, SAED, FTIR and chemical analyses, it is suggested that the quantum confinement effect of nanometer β-SiC be responsible for the blue light and violet emission     

Effect of the SiC particle size on the dry sliding wear behavior of SiC and SiC–Gr-reinforced Al6061 composites

The effect of size of silicon carbide particles on the dry sliding wear properties of composites with three different sized SiC particles (19, 93, and 146 μm) has been studied. Wear behavior of Al6061/10 vol% SiC and Al6061/10 vol% SiC/5 vol% graphite composites processed by in situ powder metallurgy technique has been investigated using a pin-on-disk wear tester. The debris and wear surfaces of samples were identified using SEM. It was found that the porosity content and hardness of Al/10SiC composites decreased by 5 vol% graphite addition. The increased SiC particle size reduced the porosity, hardness, volume loss, and coefficient of friction of both types of composites. Moreover, the hybrid composites exhibited lower coefficient of friction and wear rates. The wear mechanism changed from mostly adhesive and micro-cutting in the Al/10SiC composite containing fine SiC particles to the prominently abrasive and delamination wear by increasing of SiC particle size. While the main wear mechanism for the unreinforced alloy was adhesive wear, all the hybrid composites were worn mainly by abrasion and delamination mechanisms.     

Synthesis of High Purity SiC Powder for High-resistivity SiC Single Crystals Growth

High purity silicon carbide （SIC） powder was synthesized in-situ by chemical reaction between silicon and carbon powder. In order to ensure that the impurity concentration of the resulting SiC powder is suitable for high-resistivity SiC single crystal growth, the preparation technology of SiC powder is different from that of SiC ceramic. The influence of the shape and size of carbon particles on the morphology and phase composition of the obtained SiC powder were discussed. The phase composition and morphology of the products were investigated by X-ray diffraction, Raman microspectroscopy and scanning electron microscopy. The results show that the composition of resulting SiC by in-situ synthesis from Si/C mixture strongly depends on the nature of the carbon source, which corresponds to the particle size and shape, as well as the preparation temperature. In the experimental conditions, flake graphite is more suitable for the synthesis of SiC powder than activated carbon because of its relatively smaller particle size and flake shape, which make the conversion more complete. The major phase composition of the full conversion products is β-SiC, with traces of α-SiC. Glow discharge mass spectroscopy measurements indicated that SiC powder synthesized with this chemical reaction method can meet the purity demand for the growth of high-resistivity SiC single crystals.     

Solid combustion synthesis of β SiC powders

A method of obtainment of β SiC powders under conditions of the self-propagating high-temperature synthesis (SHS), based on the exothermic reaction between silicon micropowders and active carbon substrates (carbon black and charcoal), has been developed. The method described in the paper is characterised by a low ignition temperature (1250–1300°C) and a short duration of synthesis (3–5 minutes). The product retains the morphology of the carbon substrates used what indicates the occurrence of a mechanism similar to the one suggested in the case of carbon fibres-silicon systems, namely the occurrence of alternating steps of solution of carbon in liquid silicon and crystallisation of SiC from supersaturated solution.     

Sinter-HIP of polymer-derived Al2O3–SiC composites with high SiC contents

Submicrometer Al₂O₃ composites with more than 20 vol.% of SiC particles were produced using a multiple infiltration of porous bodies with a liquid polymer SiC precursor. The fully dense composites were successfully densified using a sinter-HIP process. Parameters of sintering and HIP steps are discussed with respect to both densification and microstructure evolution of the composites. The initial pressure during the sintering step plays an important role for the preparation of fully dense composites with a submicrometer alumina matrix at 1750 °C. Optimized densification schedule of sinter-HIP represents a novel approach of densification at relatively mild conditions compared to previously reported or common densification methods of Al₂O₃–SiC composites with high SiC content, such as pressureless sintering, hot pressing and post-HIPing. The method expands the possibilities for preparation of alumina based composites with SiC volume fraction > 20 vol.%, filling the gap in available literature data.     

Low-temperature microwave sintering of TiN–SiC nanocomposites

Densification kinetics study during microwave sintering of titanium nitride-based nanocomposite has been conducted. A series of TiN–SiC compositions with 1, 3, 5 wt% of silicon carbide were microwave sintered at relatively low sintering temperatures (900–1,300 °C) for 0–30 min. The SiC content influenced on heating uniformity and final density and grain-size achieved. Densification process during microwave sintering obeyed the mechanism of grain-boundary diffusion with activation energy of 235 kJ mol⁻¹. Microwave sintering resulted in fine microstructure (~300 nm) and hence high values of micro hardness (~20 GPa).     

The effect of size of the SiC inclusions in the AlN–SiC composite structure on its electrophysical properties

AlN–SiC–Y₃Al₅O₁₂ composite materials with a high absorption of microwave frequency (27–65 dB/cm) produced by pressureless sintering of mixtures consisting of AlN(2H), Y₂O₃, and SiC (6H) in 46, 4, 50 wt %, respectively, have been studied. The SiC components of the mixtures were used in sizes of 1, 5, and 50 μm. It has been shown that the resistivity of the developed materials depends essentially on the materials structures: sizes of SiC inclusions, distances between them, and state of the interfaces. It has been found that the increase of the SiC inclusions sizes in the material structure from 3 to 7 μm results in the decrease of the resistivity from 10⁴ to 90 Ω·m, and at the decrease of the SiC inclusions sizes from 3 to 0.5 μm there forms a SiC uninterrupted skeleton, which also decreases the resistivity to 210 Ω·m. Thus, composite materials that contain 50 wt % SiC (inclusions sizes of 3 μm) are the most efficient in producing absorbers of microwave radiation. Interlayers of yttrium aluminum garnet, which are located at the SiC grains boundaries, prevent the forming of AlN(2H)–SiC(6H) solid solutions and thus, make it possible to keep high dielectric characteristics of a composite material based on aluminum nitride and afford a high absorption of a microwave radiation.     

In situ enhancement of toughness of SiC—TiB2 composites

A process based on liquid phase sintering and subsequent annealing for grain growth is presented to obtain the in situ enhancement of toughness of SiC–30 wt%, 50 wt%, and 70 wt% TiB2 composites. Its microstructures consist of uniformly distributed elongated -SiC grains, relatively equiaxed TiB2 grains, and yttrium aluminium garnet (YAG) as a grain boundary phase. The composites were fabricated from -SiC and TiB2 powders with the liquid forming additives of Al2O3 and Y2O3 by hot-pressing at 1850°C and subsequent annealing at 1950°C. The annealing led to the in situ growth of elongated -SiC grains, due to the phase transformation of SiC, and the coarsening of TiB2 grains. The fracture toughness of the SiC–50 wt% TiB2 composites after 6 h annealing was 7.3 MPa m1/2, approximately 60% higher than that of as-hot-pressed composites (4.5 MPa m1/2). Bridging and crack deflection by the elongated -SiC grains and coarse TiB2 grains appear to account for the increased toughness of the composites.     

In-Situ Characterization of SiC–AlN multiphase ceramics

AlN and SiC can react and form a solid solution at temperatures above 1800 °C, a result that may be beneficial for sintering silicon carbide ceramics. The pressureless sintered AlN–SiC multiphase ceramics have reached high density at a temperature of 2100 °C for 1 hr in Ar. Analytical scanning transmission electron microscopy was then used to determine the grain boundary, fracture surface, and the local compositions. Because AlN has a higher solid vaporization pressure than SiC, the vaporization rate of the AlN solid would far exceed that of SiC at a sintering temperature. The vaporizing AlN was deposited on the surface of SiC powder; SiC grains then elongated in a random arrangement. The form of elongated rod crystals of 4H SiC is 5 to 8 m in length and 1 m in width. It resulted in the sample fracture section producing pulling-out and a strong tearing-open effect. The bending strength and the fracture toughness of the material obtained are 420 MPa and 4.40 MPa × m^1/2, respectively.     

Thermal stability of SiC fibres (Nicalon®)

The degradation behaviour of Nippon Carbon Co. SiC fibres (Nicalon®) after heat treatment in various environments was studied. Regardless of the heat-treatment conditions, the Nicalon® fibre strength degraded when the fibres were subjected to temperatures higher than 1200° C (temperatures below 1200° C were not investigated). This degradation is associated with the evaporation of CO from the fibres as well as with-SiC grain growth in the fibres.     

Underwater shock consolidation of Mg–SiC composites

The shock consolidation of magnesium (Mg)/silicon carbide (SiC) composites using axisymmetric explosive fabrication setup is reported. Pure Mg and SiC powders are consolidated in a three-layered cylindrical assembly with the energy being derived from a high-detonation velocity explosive. The pressure of underwater shock wave is experimentally measured and simulated using AUTODYN 2D. Microstructural characterization of the samples revealed a well-flown Mg matrix enveloping near homogeneous SiC particles. Occasional clustering of SiC particles and interparticle melting is evidenced. Results of microhardness revealed that the presence of SiC particulates led to a substantial increase in the hardness of the composite. Fractography results indicate the lack of formation of ductile dimples, which is attributed to the presence of discontinuous SiC particles. The strengthening mechanism, the absence of reaction products, the structure–property correlation of the shock consolidated composite are discussed.     

SiC/SiC晶须复合材料

日本大阪工业技术试验所玻璃陶瓷材料部开发了一种新的制造纤维增强陶瓷(SiC/SiC晶须复合材料)的方法。它先是制作成碳化硅(SiC)前驱体的聚碳硅烷(PCS)同SiC晶须的复合体,然后加热使PCS热解生成该复合材料基体的SiC,尽管还存在产品密度不高的问题,     

Effects of Nitridation on Properties of SiC Fiber and Interface of Ti Matrix Composite

Prenitridation of the TiBx coating surface of the Sigma SM1240 SiC fiber can from more stable compounds at the surface and obstruct the release of boron atoms into the Ti-based alloy matrix.The effect of nitridation on the tensile strength of the fiber was investigated in this work.Nitridation could degrade the tensile strength of the SiC if the treating temperature and time are not optimized.The chemical reaction between the W core and SiC and the modification of fiber microstructure during the nitridation are respornsible for the degradation in strength.The strength can be maintained by further optimization of the treating temperature and time.Therefore stabilizing the surface of TiBx coating and hence the interface of the SiCf/Ti composite by the nitridation of the SiC fiber is a feasible technique for practical application.     

First—principle Calculation of the Properties of Ti3SiC2

The electronic and structural properties for Ti3SiC2 were studied using the first-principle calculation method.By using the calculated band structure and density of states,the high electrical conductivity of Ti3SiC2 are explained ,The bonding character of Ti3SiC2 is analyzed in the map of charge density distribution.     

Ultrasonic Electrodeposition of Cu–SiC Electrodes for EDM

Cu-SiC composite electrodes composed of both a Cu matrix and dispersed inert SiC particles were fabricated for electrical discharge machining (EDM) using the ultrasonic-aided electrodeposition technique. The influence of ultrasonic power on the surface morphology, content of SiC particles, and EDM wear rate of the fabricated Cu-SiC composite electrode were investigated. Results show that the incorporation of SiC particles into the composite electrode was enhanced and that the uniformity of particle distribution in the Cu matrix improved when the ultrasonic dispersion was initiated during electrodeposition. The composite that was generated at low ultrasonic power contained more SiC than that produced at high ultrasonic power. Moreover, the Cu-SiC electrode fabricated at low ultrasonic power displayed the least erosion wear during EDM.     

Auger Depth Profiling of Carbonized SiC/Si Samples

Silicon carbide (SiC) has been prepared by passing natural gas over (100) oriented hot Si substrate at different temperatures in the range 930~1000℃. Reaction times of 60 and 90 min are used.Depth profile, using Auger Electron Spectroscopy, shows the formation of SiC under a thin coating of carbon for the samples prepared at 930 and 950℃. Annealing, at 1050℃ for 12 h,results in a more pronounced formation of SiC. It is found that at the temperature of 1000℃and reaction times of 60 and 90 min, a hard diamond-like coating is formed.     

Mechanical Properties and Microstructure of Diamond–SiC Nanocomposites

A bulk composite material close in hardness to diamond was fabricated from nanocrystalline diamond and SiC. The mechanical properties and microstructure of the composite were studied. Young's modulus of the composite is found to be notably lower than the one following from the additivity rule, which is attributable to the influence of structural defects present in the interfacial zone between SiC and diamond. SiC consists of nanometer-scale grains near the interface and submicron grains in the pores.     

Assessment of diffusion barriers for Ti–SiC composites

Abstract

The application of chemical vapour deposition and physical vapour deposition coatings, either singly or in combination, onto SiC fibres is discussed in terms of their ability to enhance the high temperature stability of Ti–SiC composites. The thermal stability and success of potential barrier layers was assessed by studying the fibre-matrix interdiffusion and measurement of the mechanical properties of individual fibres following coating and thermal exposure. Measurements of the level of strength retention have proved to be a reliable method of assessing the effectiveness of potential diffusion barriers. Failures may result from one of three sources. For high strength fibres failures are SiC–core reaction zone initiated, for intermediate strength fibres failures are surface defect (SiC) initiated and for low strength fibres, failures are fibre–matrix reaction zone or coating initiated. To ensure high strength (i.e. core failures) it is essential that a carbon layer is retained at the SiC surface. The most successful barriers have been shown to be TiB₂ and PtAl₂ coatings preventing outward diffusion of carbon and minimising the interaction with the titanium matrix. From these results a life prediction model has been developed based on the fibre–coating interaction, which will predict fibre strength as a function of time at a given temperature.

MST/3001     

Characteristics of Fatigue in a SiC Reinforced Aluminium Alloy

1.IntroductionMetal matrix composite materials exhibitquite a good combination of strength andstiffness of the reinforcing phase withductility and toughness of the matrix.Aluminium alloys reinforced with SiC parti-cles and whiskers are receiving a greatdeal of attention from researchers andengineers,because the engineering properties     

CVD SiC涂层SiC纤维增强SiC复合材料的研究

本文采用CVD技术对KD-1 SiC纤维作涂层处理,再通过聚碳硅烷浸渍裂解法制备单向SiCf/SiC复合材料.研究了不同沉积时间的CVDSiC涂层对SiCf/SiC复合材料性能的影响,同时运用SEM研究了SiC纤维表面SiC涂层的形貌.结果表明:经过5小时CVDSiC涂层SiCf/SiC复合材料具有良好的力学性能和抗氧化性能.