Papers by Author: Jian Yun Zhang

Abstract: SiCp/Al composite was fabricated by the method of pressureless-infiltration. In atmospheric environment, the atmospheric corrosion behavior of SiCp/Al composites (ZL101+49%SiC+5%Mg) was studied by mass loss, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and Fourier transform infrared spectroscopy (FTIR), respectivelhy.The results show that the corrosion rate of the SiCp/Al composites increases with increasing of time in atmospheric environment. Pitting corrosion is the main characteristic of SiCp/Al composite, and corrosion area gradually extends around with time increasing. At last, sheet like corrosion substrates distribute in the surface of n the SiCp/Al composites. Amorphous Al2O3 and amorphous AlxSO4yOHz are the main corrosion products.

Abstract: Diamond convex surface films were synthesized on molybdenum substrate using DC plasma Jet CVD (DCPJCVD), and their microstructure and topography were characterized by those techniques such as X ray diffraction, Raman spectroscopy respectively. It showed that, when the substrate was pre-treated by polishing using successive micron diamond powder (about 30～3μm), diamond film was a polycrystalline texture and (111) faces were dominant. Raman spectrum shows that high quality diamond convex surface film was prepared successfully. Meantime, We used Finite element methods (FEM) to simulate the velocity, pressure and temperature fields of reaction chamber respectively, and it indicated that the distribution of the velocity, pressure fields were fluctuant, which had negative influence on diamond film, but the temperature fields is uniform, and it is an important factor to prepare high quality diamond convex surface film.

Abstract: SiCp/Al composites based on different matrix elements Mg and Si content were fabricated by pressureless infiltration. Through microscope investigation by SEM and TEM, density examination, coefficient of thermal expansion (CTE) and thermal conductivity measuring by Netzsch DIL 402EP and Netzsch LFA 447 Nanoflash, the effects of Mg and Si in the aluminum on the thermo-physical properties of SiCp/Al composites was studied and analysed. The results showed that , adding Mg element in matrix enhaced the densification and thermal conductivity of composites, but meanwhile increased the CTE of SiCp/Al composites. When Mg element content was in higher than 6.3wt%, CTE of SiCp/Al composites increased obviously. Adding Si element in matrix markedly reduced the CTE of composites , but meanwhile decreased thermal conductivity of composites. When Si element content was higher than 5-9wt%,thermal conductivity of composites declined obviously. Adding Mg element in matrix improved the interface wet ability between molten aluminum and SiC particles, and adding Si element in matrix could control the formation of A14C3 which is a detrimental interface reaction product during the pressureless infiltration processing. Therefore, adding appropriate Mg in company with Si in matrix will be more benefit to enhance the integer properties of SiCp/Al composites.

Abstract: The influences of the different Si (0.723%~4.5%) and Cr (2.0%~8.0%) contents on the microstructures and properties of Cr-Si-Mn white cast iron were investigated. It is shown that with increasing of amounts of Si and Cr elements, carbide undergoes an evident change in the morphology from the continuous net to isolated stripe and becomes clearly finer, even forms chrysanthemum-like microstructure which is usually found in high Cr white cast iron. Additionally, the amounts of the carbides increase too. The XRD analysis shows that the carbides are a mixture of Fe3C and Fe7C3 phases. Furthermore, the hardness of carbide and matrix is also found to progressively increase with increasing of amounts of Si and Cr elements. The hardness of the matrix in as-cast white cast iron is over HV400, suggesting that the matrix consists of martensite and bainite phases. The impact toughness of the samples declines evidently when Si content excesses 3.0wt%. It is also revealed that the bainite matrix in the Si-Cr white cast iron has a higher impact abrasive wear resistance than others, which is almost not dependent upon heating temperature and cooling rate. When Cr content approaches 5wt%, the impact wear resistance of the new cast iron is comparable to that of the traditional high Cr cast iron.

Abstract: Al alloy reinforced with SiCp (size: 70-220μm) was fabricated by pressureless-infiltration. Its wear resistant property was investigated under different heat-treatment conditions, and morphology of worn surface was examined. The results showed that the composite was integrated, uniform and compact, and its wear resistant property was better than that of the unreinforced matrix alloy. It was indicated that some rigid SiCp in the abraded surface of the composite could support part of loads and replace matrix to wear-tear, which improved the wear resistant property. Compared to annealing, solution aging strengthens Al alloy matrix and cohesion with SiCp, and the wear resistant property of composites was better. Combining interface is also an important factor which influences on wear resistant property. During the wear test, the smaller SiCp size, the more interfaces, there are more SiCp falling off because of loosening combining interface, which results in more wear-tearing value. The wear rate of composite increases with decreasing SiCp size, thus, the composite with larger SiCp has better wear-resistant property than that with smaller SiCp. At last, the wear mechanism of the composite was also studied, and it showed that abrasive wear dominated in the abrasion process.