Papers by Author: Yong Huang

Abstract: The colloidal forming is an important process to prepare complex-shaped parts of ceramics, especially for industrialization of structure ceramics. It has been paid widely attention to by ceramic scientists, industries and governments in the past three decades. In 90’s, because the homogeneous green bodies were prepared using colloidal ways, many new colloidal forming processes were developed continuously such as gelcasting, DCC, TIF, colloidal vibration casting, colloidal injection moulding, HAS, and so on.. However, crackings of sintered bodies from colloidal ways have also often been occurred, especially for large size and solid parts of ceramics. In this paper, some important views about shrinkages from colloidal forming were discussed. The internal stresses in green bodies to prepare using colloidal forming resulted from the shrinkage of suspension during from liquid to solid. The shrinkage led to different cracks during sintering and/or debindering. Finally, it is put forward that the shrinkage from liquid to solid in colloidal froming have to be regarded in the future.

Abstract: By means of a finite element method model, the effects of property parameters of refractory on thermal stress of injection lance have been studied. The results show that the maximum thermal stress increases with the improvement of thermal conductivity and elastic modulus of refractory, while it decreases at first and then increases with the improvement of the coefficient of expansion of refractory.

Abstract: In this work, the reaction between Ti3AlC2 and Cu in the synthesis process of Cu/Ti3AlC2 composites has been studied. According to the results of XRD, SEM and EDS, Ti3AlC2 reacts easily with Cu to generate TiC and intermetallic compound Cu9Al4 when the holding temperature is higher than 950°C, no matter how much Cu is contained. In addition, when the content of Cu increases, more layered Ti3AlC2 grains react with Cu and form irregular shaped grain containing Cu, Ti, Al and C elements. Therefore, the Cu/Ti3AlC2 composites cannot be synthesized above 950°C by hot-pressed method if no specific treatment is used.

Abstract: The morphologies and textures of the pyrolytic carbon matrix in 2D-C/C composites after graphitization were investigated by means of polarized light microscope (PLM) and high resolution transmission electron microscope (HRTEM). The microstructure parameters of the pyrolytic carbon matrix before and after graphitization were characterized with X-ray diffraction (XRD) technology. It was found that the interplanar distance of (002) planes (d002) of pyrolytic carbon matrix decreases, and the microcrystalline stack height (LC) increases after graphitization. Graphitization treatment resulted in a coarsening of the surface texture and in the formation of circumferential cracks within the matrix. The lattice fringes of the pyrolytic carbon matrix are continuous and longer in each domain and the (002) peak spot is smaller and more intense after graphitization.

Abstract: MgAlON ceramics were prepared by spark plasma sintering (SPS) and hot pressing (HP), respectively. It was found that SPSed MgAlON samples had a single MgAlON phase with almost no open pore while HPed MgAlON had a minor AlN phase. The strength of SPSed samples is higher than 500MP, being much higher than that of the HPed samples. The experimental results revealed that that SPS was a rapid and reliable process for the further development of MgAlON.

Abstract: A heated sprue device for ceramic injection moulding was used to research the defects in injection-moulded technical ceramics. By use of the heated sprue device, the problem of sprue solidification was resolved and the density of the injection moulding specimens was increased while the defects eliminated. The influence of the processing parameters on the defects of the injection molding specimens was investigated in detail by X-ray radiography camera and photograph. It turns that the sprue solidification time has much influence on the defects in injection-moulded technical ceramics. Reasons causing the results above were also analyzed. Based on the research, bars of 20mm in diameter without macroscopic defects and turbine blade of fine property with Si3N4/SiC(w) materials were prepared by injection moulding.

Abstract: Two kinds of commercial alumina compacts made by injection molding with different solid loading are studied. Solid loading is the key factor for the injection molding process and the properties of green body and sintered compacts. The results show that higher solid loading leads to better properties of the compacts such as density and fracture strength, however the viscosity of the feedstock would increase. Smaller sized alumina powder leads to a higher critical solid loading value. Macroscopic defects such as voids and cracks could be introduced into the injection molding samples if the molding variables are not optimized. The properties of sample are improved by adjusting the variables such as injection pressure, holding pressure, holding time and barrel temperature.

Abstract: According to the heat transmission theory, in the aid of computer, the temperature distribution in the cylinder cavity was calculated. The temperature of the mould has much influence on the time for the injection material’s temperature of the cavity center to drop to the injection material softening temperature. The influence of the processing parameters on the density of the injection molding specimens was also investigated. It turns that the injection molding specimens’ density changes little with the increase of injection temperature and pressure, but changes a lot with the increase of holding pressure time.

Abstract: Extrusion gelation freeform fabrication (EGFF) is a new solid freeform fabrication technique to fabricate ceramic parts. The study of ceramic suspensions rheological behavior is essential to a better understanding of parts fabrication through EGFF process. In this paper, the effects of dispersant concentrations, solids loading and binder composition on the rheological behavior of alumina suspensions were examined. The optimal amount of dispersant was found to be about 0.1 wt.%. The suspensions with 50 vol.% alumina and 1wt.% sodium alginate show shear thickening behavior. Such behavior is unfavorable for extrusion gelation freeform fabrication. By addition of PVA or styrene-acrylic latex, the rheological behavior of suspensions was changed. The addition of PVA or latex has a great effect on the viscosity of the suspensions and the type of their rheological behavior. The ceramic suspensions with PVA or latex were found to be shear thinning more suitable for EGFF.

Abstract: High-pure bulk Ti3SiC2 samples were fabricated by directly hot-pressing (HP) high-pure Ti3SiC2 powder without any additives at 1200°C to 1500°C for 0.5–2 hours in flow argon atmosphere. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used for phase identification and microstructure evaluation. The fabricated Ti3SiC2 materials have relative high density with high purity, flexural strength of 500-700MPa and fracture toughness of 9-12MPa·m1/2. The influence of sintering temperature and soaking time on the mechanical properties of Ti3SiC2 materials was discussed. The sintering mechanism for Ti3SiC2 powder without any additives was considered to be related with the fragile-ductile transformation of Ti3SiC2 at 1100°C.