Abstract: Carbon fiber is mainly distributed in the shape of short fibers and unidirectional fibers as the reinforcing phase in metal matrix composites, and it is seldom studied as woven-cloth shaped to reinforce the matrix. In this paper, the pretreatment and the surface metallization of the woven carbon fiber were studied. Besides, the casting experiment without external pressure was carried out under the application of magnetic field. The result shows that when burning about 45mins at 500°C in the atmospheric environment, the pretreatment can achieve the best result according to differential thermal analysis and weight-time variation curve. Meanwhile the surface wettability between the carbon fiber and the matrix is greatly improved after the surface treatment and at the same time the reaction between the carbon fiber and molten aluminium alloy matrix is necessarily avoided, and it can consequently achieve an excellent bonding between the woven carbon fiber and aluminium alloy matrix. The application of magnetic field also provides magnetic force to promote the penetration of the molten matrix into the carbon fiber bundles.
Abstract: In this article, the high-performance modified AlN powder was prepared, using Y(NO3)3·6H2O as the modifying agent, and characterizing by pH meter, TG , XRD and SEM. The results show that the Y2O3 coating was formed on the AlN surface, the pH value of aluminum nitride of treatment suspension solution maintains 7.75 in water bath for 100 hours. Therefore the conclusion is that surface modification with rare earths can effectively inhibit the hydrolysis of the AlN powder.
Abstract: AlN/Cu composite powder was prepared by ball milling method. Laser particle size analyzer, X-ray diffraction and scanning electron microscopy analysis were performed to study AlN/Cu composite powders. The effects of rotation speed, mixing time, and ball to powder weight ratio (BPR) on the particle size distribution, composition, and morphology were investigated. Results showed that the best ball milling parameters were the rotation speed of 200r/min, mixing time of 6 hours and BPR 10:1. In this best condition, AlN/Cu composite powders would be obtained with optimum particle size distribution and morphology. Then composite powders were pressed at 500MPa and sintered at 1000°C in N2 atmosphere. Finally, the composite with an AlN content of 33wt% showed the bending strength of 370MPa, Vikers hardness HV154, thermal conductivity of 182.7W/m°C and electrical conductivity of 3.08MS/m. However, the composite with an AlN content of 25wt% showed the bending strength of 329MPa, Vikers hardness HV122, thermal conductivity of 195W/m°C and electrical conductivity of 6.54MS/m.
Abstract: In this paper, a remelting and diluting (RD) approach was used to fabricate in situ A356-3wt.%TiB2 composites and the effect of Sr and La on the modification of the composites is investigated in comparison with the conventional flux assisted synthesis (FAS) approach. The microstructure was examined and tensile properties were tested to evaluate the modification efficiency on the composites. The results demonstrated that composites fabricated via RD approach achieve preferable modification by Sr and La due to the higher level of melt cleanliness so as to minimize the Sr-B interaction, in which the eutectic Si which displays a microstructure with globular-fibrous eutectic Si particles. Superior mechanical properties are obtained in the RD composites (especially the elongation) after modified by Sr and La.
Abstract: In order to efficiently fabricate dense three-dimensional carbon fiber reinforced mullite matrix composites (3D C/mullite), two kinds of Al2O3-SiO2 sols with high solid content were used as raw materials. The ceramic yield and mullitization behavior of the sols and the densification process were investigated. It is indicated that the two sols have proper solid content and ceramic yield and can be completely transformed into mullite at 1573K, which make them be able to prepare composites. 3D C/mullite composites with a porosity of ∼25% were prepared by repeating less than 20 cycles of infiltration-drying-heating of sols, and the microstructures and mechanical properties were examined. The results suggest that the sol with smaller particle size derived composites exhibit well-sintered dense matrix and physically stronger interfacial bonding, which are beneficial to improve load-bearing and load-transferring capacity of matrix. As a result, this composites show much higher mechanical properties. The flexural strength and modulus are 2.4 times and 1.3 times as those of the sol with larger particle size derived composites, respectively.
Abstract: Silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC) were fabricated by precursor impregnation and pyrolysis (PIP) process with a new precursor polymer, liquid polyvinylcarbosilane (LPVCS). The molding process was conducted during the cross-linking reactions of LPVCS for the first PIP cycle. The influences of molding pressure and molding time on the flexure properties of the SiC/SiC composites were studied. The results indicated that the optimal molding pressure and molding time were 3MPa and 5h respectively due to the fine interfacial bonding between fiber and matrix. The density of the SiC/SiC composites was 2.16g/cm3. The flexural strength and fracture toughness of the SiC/SiC composites were 637.5MPa and 29.8MPa·m1/2 respectively.
Abstract: Si3N4-BN composites were prepared by die-pressing and precursor infiltration and pyrolysis (PIP) route using borazine as the precursor. The composition, microstructure, mechanical, and dielectric properties of the composites with different porosities were investigated. With the adoption of starch as pore forming substance, drawn the Si3N4 preform from the liquid precursor borazine and decrease the pressure during curing, the porosity of the Si3N4-BN composites were effectively increased. Along with the increase of the porosity of the composites, the mechanical properties were decreased and the dielectric properties were improved. With 20 wt.% starch and drawn Si3N4 preform from borazine before curing, the density, porosity, flexural strength and elastic modulus of the composites were 1.70 g·cm-3, 29.78%, 48.05MPa and 32.45GPa, respectively. The dielectric constants and loss tangents were 4.20~4.44 and 0.48~3.42×10-3 at the frequency 7~ 18GHz. Composites with various dielectric and mechanical properties can be designed and prepared according to the application needs.
Abstract: Al2O3 particles reinforced ZL109 composites were prepared by in-situ reaction between Fe2O3+MnO2 and Al in this paper. The influence of ratio of Mn to Fe on the morphologies of Al-Si-Mn-Fe phase and mechanical properties of the composites was investigated. The microstructure was studied by electron probe micro-analyzer (EPMA) and transmission electron microscopy (TEM). The results show that the Al2O3 particles displaced by the Fe2O3+MnO2/Al system are in nanosize. The acicular Al-Si-Fe phases change from acicular to polygonal shape and become smaller with the increase manganese content. The hardness test results have no big difference on the composites. However, the ultimate tensile strength at room temperature and 350°C enhance evidently with the increasing of Mn/Fe.
Abstract: In order to improve the tribological properties of aluminum alloy cylinder wall, Ni-base coatings were fabricated by atmospheric plasma spraying on aluminum substrate. The composition, microstructure characterization and tribological properties of Ni-base coatings were investigated under different lubrication conditions. The results showed that as-sprayed Ni-based coatings were mainly consisted of γ-Ni solid solution, Ni3B, Cr7C3, Cr6C and Cr3B2 phase. The microstructure of coatings exhibited excellent deposit integrity and density, whilst a typical lamellar structure was observed because the molten droplets successively impinged and spread on the substrate or previously deposited layers to form continuous splats. Friction and wear testing results showed that Ni-based coating performs better than grey cast iron HT200 for the actual application of cylinder block and cylinder liner, especially under boundary lubrication. It was proposed that the excellent mechanical properties ensure the as-sprayed coating with low friction coefficient and wear rate under different lubrication conditions, In addition, the existence of pores was benefitted for the improvement of tribological properties under boundary lubrication.