Papers by Author: He Guo Zhu

Abstract: NiAl matrix composites reinforced with a-Al2O3 and TiB2 were fabricated by microwave synthesis from Al-TiO2-B-Ni system. The reaction process and microstructures were analyzed by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM).The results showed that the ignition temperatures of the reaction heating by microwave and conventional method were approximately 556°C and 592°C respectively. Furthermore, the fabrication time by microwave synthesis was about several minutes, which was much shorter than two hours spent usually in conventional heating method. The a-Al2O3 phase aggregated at the trigonal grain boundary of the NiAl matrix, and the TiB2 phase distributed uniformly in the NiAl matrix.

Abstract: In situ aluminum matrix composites were fabricated through exothermic dispersive (XD) reaction from a powder mixture of Al and Cr₂O₃. The reaction mechanism was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS) and differential scanning calorimetry (DSC) analysis. When the temperature increases to around 1050K, Al can react with Cr₂O₃ to form the reinforcments Al₂O₃ particles and CrAl₄ blocks. With the increase of heating rate, DSC analysis shows that the reaction peak shifts to a higher temperature and the corresponding ignition temperature also increases. Based on DSC curves with different heating rates, the activation energy can be calculated and its value is 191.8 kJ/mol.

Abstract: The amount of SiO₂ on the thermal resistance of the ceramic lined cast pipe fabricated by self-propagating high temperature synthesis technology was investigated. Results indicated that the ceramic-lined composite cast iron pipe had excellent thermal resistance. With the increase of the additive SiO₂ amount, the thicknesses and cavity of the ceramic liner increased, which led to the increase in their thermal resistance. In a given ceramic-lined composite cast iron pipe, its thermal resistance increased with the increase of the center temperature.

Abstract: The composite (a-Al2O3+ZrC+ZrB2)/Al has been fabricated by using exothermic dispersion synthesis. When the reinforcement volume fraction is 100%, there are two exothermic peaks occurred in DSC curve of the Al-ZrO2 system. But when the reinforcement volume fraction is 30%, there is only one exothermic peak occurred in the DSC curve and the height of it decreases. When the molar ratio of B4C/ZrO2 is 0, the reaction products are consisted of a-Al2O3 grains and Al3Zr blocks. With an increase in the molar ratio of B4C/ZrO2, the amount of the Al3Zr decreases and the phases of ZrB2 and ZrC are formed. When the molar ratio of B4C/ZrO2 increases to 1/3, the Al3Zr almost disappear and the reinforcements of the composites are composed of a-Al2O3, ZrC and ZrB2. The corresponding XRD (X-ray diffraction) patterns also testify this.

Abstract: The reaction mechanism of an Al-TiO2 system is discussed. Thermodynamic analysis indicates that the reaction between Al and TiO2 can occur spontaneously due to the negative Gibbs free energy of the Al-TiO2 reaction system. When the reinforcement volume fraction is 30%, there is an endothermic peak and an exothermic peak in the DSC curve. But when the reinforcement volume fraction increases to 100%, there are two independent exothermic peaks and the height of them increases obviously. With increasing the heating rate, the ignite temperature becomes higher and all the peaks move to the higher temperature direction. The reactions between Al and TiO2 consist of two steps: first, Al reacts with TiO2 to form the stable α-Al2O3 particles and the active Ti atoms; second, the active Ti atoms react with Al to form Al3Ti.

Abstract: Wear is the primary cause of the failure of joint replacement prostheses. In this paper, the ultra-high molecular weight polyethylene (UHMWPE) as an artificial joint acetabular material was filled with nano-powder of SiO2 of various mass fractions. The effect of SiO2 mass fraction on the tensile strength, tensile modulus, wetting property and tribological properties of the SiO2-UHMWPE composites were investigated when sliding against Ti-6Al-4V under lubrication of physiological saline water. The morphologies of the worn surfaces of composites were observed with optical microscope. As a result, the tensile strength, tensile modulus, wettability and wear resistance of the composites were all improved by filling with SiO2, and the composites had largely decreased friction coefficients under lubrication of physiological saline water compared with the unfilled UHMWPE. This was attributed to the reinforcing function of the nano-powder of SiO2 in the composites and the lubricating action of the water boundary film. The wear of pure UHMWPE was dominated by plowing, plastic deformation, while the SiO2-UHMWPE was characterized the mild fatigue wear.