Feng Yi

Vacuum Brazing Processes of Aluminum Foam

Abstract Butt joints of aluminum foam were made by three different brazing processes including brazing with multilayer filler metal in high vacuum of 10−3 (Pa) degree, brazing with multilayer filler metal in low vacuum of 1 (Pa) degree and brazing with monolayer filler metal in high vacuum of 10−3 (Pa) degree. The macrostructure and microstructure characteristics and bending strength of the joints were investigated and compared. The results indicate that the brazed specimen can achieve a satisfactory joint when brazed with multilayer filler metal in high vacuum. The bending strength of the joint is higher than that of the base metal. However, the bending strength of the joint is obviously lower than that of the base metal when brazed with multilayer filler metal in low vacuum, while it is slightly lower when brazed with monolayer filler metal in high vacuum.

Fabrication of Magnetic Fe3O4 Nanotubes by Electrospinning

Abstract Ferroferric oxide nanotubes were prepared by calcining and reducing the composite nanofiber precursors fabricated by electrospinning. Influences of the electrospun parameters (PVA concentration of solution, applied voltage and collector distance) on the preparation of the composite nanofiber precursors were discussed. The structural properties of the obtained nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation mechanism of the Fe3O4 nanotubes was investigated through the nonequilibrium heat-treatment procedure. Furthermore, the magnetic property of Fe3O4 was measured using a vibrating sample magnetometer. Results reveal that the tubes show a uniform and continuous morphology, whose outer and inner diameters are about 100 nm and 50 nm, respectively. Fe3O4 possesses saturation magnetization (Ms) of 54.2 A·m2/kg, coercivity (Hc) of 215×79.6 A/m and remanent magnetization (Mr) of 12.8 A·m2/kg, respectively.

Reactive Synthesis of Polycrystalline Ti3AlC2 and Its Sintering Behavior

Abstract A method for fabrication of ternary compound Ti3AlC2 powder by pressureless calcining (PC) technique was developed. Powders of Ti, Al and TiC were mixed as staring materials. The effects of calcining temperature and aluminum content on the purity of Ti3AlC2 were discussed. The reaction mechanism and the microstructure evolution of Ti3AlC2 prepared at different temperatures were investigated by X-ray diffraction, field emission scanning electron microscopy and high resolution transmission electron microscopy. Results indicate that the single-phase polycrystalline Ti3AlC2 powders are obtained at 1300 °C, which possesses a typical laminated structure, and the best molar ratio of raw Ti/Al/TiC materials is 1:1.2:2. The bulk samples sintered by hot pressing were from the Ti3AlC2 powders. After hot pressing of different temperatures, the fully dense bulk Ti3AlC2 shows the best properties when prepared at 1300 °C. The density of bulk Ti3AlC2 reaches to 99.9%. The average Vickers hardness is around 5.7 GPa, and the maximum flexural strength is over 630 MPa. Finally the strengthening mechanism of the bulk Ti3AlC2 was also proposed.