Papers by Author: Hai Yan Du

Abstract: Porous mullite were prepared by coating Al(OH)3 on the surface of the particles of waste fly ash. The effects of content of urea on formation of mullite and sintering temperature on microstructure of mullite were investigated by XRD and SEM analysis. It was showed that two kind mullite were obtained, one was growing from original Needle-like mullite existing in original ashfly, and the other was formed through by the reaction between glassy phase and Al2O3 coated on spherical waste fly ash.

Abstract: Porous SiO2 ceramics had been successfully prepared by gelcasting. The open porosity of obtained samples was between 0.40 and 0.46, which reached its maximum at 1100°C. The change of line shrinkage rate was opposite to the open porosity. The microstructure was investigated though X-ray diffraction (XRD) and scanning electronic microscope (SEM).

Abstract: TZP/SUS304 functionally graded material (FGM) was developed by slip casting. Microscopic observations demonstrated that the chemical composition and microstructure of TZP/SUS FGM distributed gradually in stepwise way, eliminating the macroscopic ceramic/metal interface occurred in traditional ceramic/metal joint. Each interface of layers connected well without evident defects, and the mechanical properties of TZP/SUS system strongly depended on constitutional variation.

Abstract: Based on the relation between the stress intensity factor Ki and the crack velocity V, lifetime prediction and control were discussed and studied for machinable Ce-ZrO2/CePO4 ceramics. The relationship among lifetime, starting cracks and grain sizes were investigated by a set of designed simulation setting with a definite actual environmental conditions. It was concluded that crack started from larger weak interfaces of two phases and linking of cracking weak interfaces each other, and the lifetime of Ce-ZrO2/CePO4 composites could be controlled and predicted by adjusting of grain sizes of CePO4, which was depended on design of composites.

Abstract: Some useful characteristics, including strength, toughness, damage of machining, and propagation pattern of indentation cracks, were studied based on machinable 30 wt%LaPO4/ Al2O3 composites. Corresponding characteristics for Al2O3 ceramic were also concerned for comparing. The results supplied some elementary information for both use and further study of LaPO4/ Al2O3 composites.

Abstract: For the nano-ZrO2 powders, it is difficult to disperse the particles in a highly concentrated electrolyte. Polymer MZN with composite structure was employed as a dispersant in this work. On the basis of having obtained the optimum quantity of dispersant MZN, the effects of process conditions on stability of Ni-ZrO2 composite electroplating bath were investigated via sedimentation experiments and SEM micrograph. The results showed that the charging sequence have a significant influence on the stability of composite electroplating bath, and the optimum process conditions is that the stable aqueous suspension of 2.5g nano-powders in 100 ml water should be prepared at first by milling for 3 hours, and then the electrolytes were added in it. The well-dispersed composite electroplating bath was obtained, which made sure that the nano-ZrO2 smaller than 30nm was found in the Ni matrix.

Abstract: A new method is proposed for machinability comprehensive evaluation of engineering ceramic materials based on digraph theory. Machinability attributes of the materials are taken as the nodes and the correlations between attributes are taken as the edges. The digraph model for machinability evaluation of ceramics is set up. According to the diagraph model, the machinability attribute matrix was constituted. Then machinability indexes of ceramic materials were calculated with permanent function and machinabilities of the ceramics were evaluated. In this paper, mechanical property parameters of ceramic materials, including hardness, fracture toughness and elastic modulus, were selected as machinability attributes. Machinability of four typical engineering ceramics were evaluated and ranked with machinability indexes. The grinding experiments give further proof of evaluation results.