Papers by Author: Xiao Feng Wang

Abstract: Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with powder mixtures of Ti, Al, TiO₂ and Cr₂O₃ as raw materials. The effect of sintering temperature on the microstructures and mechanical properties of Al₂O₃/TiAl composites has been investigated. The results show that the Rockwell hardness and density of the composites increased with increasing sintering temperature. But the flexural strength and fracture toughness peaked at 825 MPa and 7.29 MPa·m^1/2, respectively, when the sintering temperature reached to1300 °C.

Abstract: Al2O3/TiAl in situ composites were successfully prepared by vacuum hot-pressing method with elemental powder mixtures of Ti, Al, TiO2 and Fe2O3. The effect of Fe2O3 addition on the microstructures and mechanical properties of Al2O3/TiAl composites has been investigated. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites increase with increasing Fe2O3 content. When the Fe2O3 content is 0.84 wt %, the flexural strength and the fracture toughness reach the maximum value of 624 MPa and 6.63 MPa·m1/2, respectively. The improvement of mechanical properties is firstly associated with a more homogeneous and finer microstructure developed by addition of Fe2O3; secondly, it is related to the increase of the ratio of α2-Ti3Al/γ- TiAl matrix phases.

Abstract: The GaOOH Nanocrystal rods were successfully synthesized by microwavehydrothermal method using Ga2O3 ,HNO3 and NH3·H2O as raw materials. Simple heat treatment of GaOOH in the flow of NH3 gas leads to the formation of submicron GaN rods even at 800°C through GaOOH. The resultant GaOOH and GaN nanomaterials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism of GaOOH and GaN was proposed. The results indicate that the as synthesized GaN were hexagonal nanorods with average aspects ratio of 5:1(diameter 800 nm and length about 4μm). Photoluminescence spectrum shows that a blue emission peak originates at 473.5 nm, indicating that the GaN nanorods displayed luminescence emission in the blue-violet region, which was related to crystal defects, and may be helpful for electro-optical applications of GaN material.

Abstract: Effects of rare-earth oxides addition (0.38~1.52 mol% of Sm2O3, Eu2O3 and Er2O3) on the property and microstructure of the hot-pressed (1300°C, 2h, 35 MPa) Al2O3 (12 wt %)/TiAl insitu composites have been investigated. The results show that the doping of rare-earth oxides has a positive effect on both mechanical properties and densities of Al2O3/TiAl composites. Densities enhanced with increasing of rare-earth oxides. The flexural strength and fracture toughness were higher than other samples when the rare-earth oxide content was 0.38 mol %. The matrix grains and Al2O3 particles were significantly refined, and Al2O3 particles evenly distributed in the matrix.

Abstract: Al₂O₃/TiAl composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al, TiO₂ and Cr₂O₃. The effect of Cr₂O₃ addition on the microstructures and mechanical properties of Al₂O₃/TiAl composites has been characterized. The results show that the Rockwell hardness, flexural strength and fracture toughness of the composites increase with increasing Cr₂O₃ content. When the Cr₂O₃ content is 3.5 wt %, the flexural strength and the fracture toughness reach the maximum value of 658.7 MPa and 7.2 MPa•m^1/2, respectively. The improvement of mechanical properties is firstly associated with a more homogeneous and finer microstructure developed by addition of Cr₂O₃; secondly, it is related to the increase of the ratio of α₂-Ti₃Al/γ- TiAl matrix phases.

Abstract: In this work, the composites were fabricated by in-situ synthesis reaction and hot-pressing using Ti, Al, TiO₂ and Eu₂O₃ as starting materials. Effects of the sintering temperature on the microstructures and properties of the Al₂O₃/TiAl composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and universal properties tests. The result shows that the sintering temperature had effect on improving the mechanical properties of TiAl composites. The phase of the composites composed of γ-TiAl/_α2-Ti₃Al matrix and reinforcing phases of Al₂O₃ and EuAlO₃. The grain size of composite was smaller than 0.5 µm at 1200 °C. And the mechanical properties reached to the maximum value (477.96 MPa and 9.73 MPa•m^1/2). The properties decreased with grain growth at 1300 °C.