Papers by Author: Zhi Meng Xiu

Abstract: Si₃N₄-Ti(C,N) nanocomposites fabricated by vacuum hot pressing with Al₂O₃ and Y₂O₃ as additives were investigated. The results showed that the α-Si₃N₄ phase converted completely into whisker-shaped β-Si₃N₄ grains after vacuum sintering at 1700°C. Suitable addition and well dispersion of the Ti(C,N) particles can restrained the lateral growth of the β-Si₃N₄ grains, increasing aspect ratio of the β-Si₃N₄ grains and improving bending strength of the composites. Fracture toughness of the composites is higher than that of the β-Si₃N₄ ceramics, and the main toughening mechanism is crack bridging due to the higher aspect ratio of the β-Si₃N₄ grains.With the addition of 1vol% of Ti(C,N), the composite has a relative density of 99.31%, Vicker’s hardness of 15.9 GPa, bending strength of 993 MPa, and fracture toughness of 9.9 MPa·m^1/2.

Abstract: (HAp/SiO2)/Ti biocomposites were prepared by the powder metallurgy method. The phase compositions and the in vitro bioactivity of such biocomposites were systematically characterized. The XRD result shows that the phase compositions of (HAp/SiO2)/Ti composites are mainly composed of Ca4O(PO4)2 (TTCP), Ti, TiO2 and CaO. The synthesized (HAp/SiO2)/Ti biocomposites exhibit a good bioactivity, for example, after the samples are immersed in SBF solution only for 24 hours, the bone-like layer consisting of spherical apatite crystal clusters has deposited on the surface of the samples. The density and thickness of the apatite layer increases with increasing immersion time. The formation process and mechanisms of bone-like apatite layer are also discussed.

Abstract: The effect of purity of amorphous boron raw materials on properties of the hot pressed SiC doped MgB2 superconductor was investigated. MgB2 superconductors with magnetic Jc over 106 A/cm2 and remaining Jc of 105 A/cm2 at 4.2 K and 5 T were fabricated by hot pressing using both high purity (99.00%) and low purity (88.84%) boron powders. XRD analysis shows that purity of the boron powders has little effect on phase component of the MgB2 samples. If the main impurity in amorphous boron is Mg, low purity low cost boron powder is suitable as one of the raw materials for fabricating MgB2. Particle sizes of boron has significant effect on microstructure and properties of MgB2. Smaller boron particle size leads to smaller grain size of MgB2, higher density, higher lattice distortion, and thus higher magnetic Jc.

Abstract: This paper presents a study on the densification and mechanical properties of Al2O3/Ti(C,N) ceramics processed using a pressureless sintering technique. The Al2O3/Ti(C,N) ceramics containing 10, 20, 30 and 40 wt% Ti(C,N) were sintered in the temperatures ranging from 1500 to 1750 °C and in the atmospheres of vacuum, Ar, H2 and N2. It is found that both optimum sintering temperature and Ti(C,N) content exist, where the best densification and mechanical properties are achieved. The Al2O3/Ti(C,N) properties will decrease when either sintering temperature or Ti(C,N) content moves away from their optimum value. The experimental results also demonstrate that among the four atmospheres, Ar gives best results. To improve further the properties of Al2O3/Ti(C,N) composites, Al2O3 and Al2O3/Ti(C,N) powders have used to cover the specimens during sintering, and experiments revealed that covering with Al2O3/Ti(C,N) powder can significantly improve the properties of Al2O3/Ti(C,N) ceramics. Furthermore, the effects of Ti(C,N) content and sintering conditions on densification and mechanical properties are explained in terms of their influences on Al2O3/Ti(C,N) microstructures.

Abstract: Hydroxyapatite (HA) powder was synthesized by a sol-gel method with Ca(OH)2 and H3PO4 as reactants. The HA granules were then coated with TiH2 powder using a mechanical mixing method. The HA-TiH2 material system produced HA-Ti composites after hot-pressing at 1050°C. The HA-Ti composites are mainly composed of HA and Ti, with small amounts of Ca2P2O7 and Ca3(PO4)2 phases. Fracture toughness and bending strength are 2.4 MPa·m1/2 and 54.3 MPa, respectively for the HA-20vol%Ti composite, higher than those of the pure HA ceramic. The improvement in properties is because of the unique 3D network structure of Ti, which is an ideal reinforcement structure for the weak and brittle HA. According to ISO/TR 7405-1984, hemolysis test was performed to evaluate the blood compatibility of the material. The results show that the hemolysis rate of the HA-20vol%Ti composite is 0.56%. Relative growth rates (RGR) of L-929 cells soaked after 6 days in the HA-20vol%Ti group, pure Ti group, black group and pure Pb group were 132%, 100%, 90% and 6% respectively, while the level of cytotoxicity was grade 0 in HA-Ti composite group. These results imply that the HA-20vol%Ti composite has good biocompatibility and bioactivity.