Papers by Author: Tian Ying Xiong

Abstract: TiO₂ is a promising photocatalyst with great potential for environment purification and energy conversion. TiO₂ coatings have more advantages over powders in practical use. Cold spraying is an ideal technique to fabricate TiO₂ coatings because of its low heat input compared with thermal sparing which may induce undesirable phase transformation from anatase to rutile. The paper will give a short introduction on recent development of TiO₂ coatings by cold spraying. Then, the factors affecting the quality of coating should be analyzed. And finally, the bonding mechanism of cold sprayed TiO₂ coating on metal substrates will also be proposed.

Abstract: Supersonic Particles Bombarding (SSPB) can introduce severe plastic deformation on the surface of metallic materials, and nanostructured surface layer can be fabricated on the materails. So SSPB is a promosing technology which can be applied in industry. Main parameters of SSPB were optimized by orthogonal design, and their effect on the weight loss of the SSPB treated sample was analysed. Optimized parameters were obtained after the orthogonal experiments.

Abstract: Generally, there are two ways available for porosity measurement of porous metals. One is by calculating density ratio of a porous metal and a corresponding non-porous metal, called as relative density method. The other is by counting the percentage of pores on cross section of a porous metal, called as image analysis method. In this work, both methods were employed for lotus-type porous copper on porosity measurement. The effects of several parameters in both methods on porosity values of the porous copper are reported and discussed. The relative density method is recommended as porosity by this method is more reliable for the porous copper.

Abstract: Severe plastic deformation can be introduced on the surface of metallic materials, and nanostructured surface layer is induced, which incorporates the surface modification technique with nanomaterials. The severe plastic deformation method-Supersonic Particles Bombarding (SSPB) was used to treat the anealled 40Cr steel. The surface microstructure and area where is about 50μm away from the top suface of 40Cr steel after SSPB treatment were characterized by transmission electron microscopy (TEM). Wear resisting property lubricated by liquid paraffin (LP)+0.3%ZDDP of SSPB sample was studied. Equiaxed nanocrystallites with random crystallographic orientation were obtained on the top surface of SSPB treated 40Cr steel. Ferrite and pearlite were deformed severely at the depth about 50μm away from the top suface, and cementite in the pearlite shows plasticity. Wear loss of polished SSPB sample is the lowest and that of untreated sample is the biggest.

Abstract: Cold Gas Dynamic Spraying (CGDS) has been developed to fabricate surface coating as a new technique in recent years. In this paper, aluminum bronze particles were sprayed on 45 steel and 316L stainless steel by CGDS, and the coating was sucessfully fabricated on the surface of the steels. The microstructure of the coating and the interface between the coating and the substrate were investigated by scanning electron microscope (SEM), energy dispersive (EDX) and XRD. It was found that the coating was dense and its porosity was low, while the microhardness of the coating was lower than that of the bulk one; Mechanical bonding was the main formation mechanism of the coating, and there was metallurgical bonding too; Diffusion occured at the interface between the coating and substrate; α phase in aluminum bronze particles transformed to β phase after the spray and the transformation was induced by the plastic strain during spraying.

Abstract: Cold spray is a new surface engineering technology. In this paper, pure copper particles were sprayed on the Al substrate by this method and the copper coating was deposited sucessfully on the surface of the substrate. The microstructure of the coating and the interface between the coating and the substrate were observed by optical and scanning electron microscopes, and the phase was identified by XRD for the pure copper particles and the coating. The microhardness of the coating is measured. The results show that mechanical bonding is the main mechanism for the interface between the coating and the substrate, and there is a few metallurgical bonding for the interface; the coating is dense and its porosity is less than 0.4%; XRD results indicate that there is no oxidation occurred during the spray process. The microhardness of the coating is about 160Hv, which is higher than that of the as-casted copper.

Abstract: Nitrogen-doped titania nanotubes (TiO2-xNx NTs) were synthesized by the soft chemical process, in which nitrogen-doped titania nanopowders (TiO2-xNx NPs) reacted with strong alkaline solutions (10M). The properties of TiO2-xNx NTs were examined. Experiments on the photodegradation of methylene blue (MB) and sulfosalicylic acid (SSA) were also carried out under visible light irradiation.

Abstract: A nanostructured layer can be introduced on the surface of metallic materials by surface severe plastic deformation. A surface severe plastic deformation method-Supersonic Particles Bombarding (SSPB) was used to treat the anealled 40Cr steel. The surface and cross sectional microstructure of 40Cr steel after SSPB treatment were characterized by means of X-ray diffraction, optical microscopy and transmission electron microscopy equipped with a Kikuchi line program to determine the grain orientations. Equiaxed nanocrystallites with random crystallographic orientation were obtained on the top surface of 40Cr steel after SSPB treatment. The surface microstructure was composed of nanostructure area, deformed area and matrix. Geometrically necessary boundaries and incidental dislocation boundaries were formed in the deformed ferrite at the distance to the surface of about 50-60μm, and the original coarse ferrite grain was divided into lamaller structure.

Abstract: Porous copper with elongated cylindrical pores were fabricated by a unidirectional solidification method in a mixture of hydrogen and argon with high pressures. The porous copper with longitudinal pores and radial pores were compared on structure. The effect of both hydrogen pressure and argon pressure on structure of the porous copper including pore size, pore density, and porosity was investigated. The reason for the effect is explained.

Abstract: Nano-sized nitrogen-doped Ti-W mixed oxides (N-TiO2-x%WO3) were prepared by soft chemical method, and their intrinsic characteristics were investigated using XRD, TEM, N2 adsorption and desorption isotherms, UV-Vis diffuse reflectance spectra and XPS. Experiments on photodegradation of Methylene Blue (MB) under visible light irradiation were carried out to evaluate the photocatalytic abilities of N-TiO2-x%WO3. Chemical Oxygen Demand (COD) analysis was also performed to evaluate the mineralization abilities of N-TiO2-x%WO3. It is shown that the N-TiO2-x%WO3 exhibited higher COD removing rates compared with Degussa P25. The color bleaching rates of N-TiO2-x%WO3 were equal to that of Degussa P25. The enhanced photocatalytic activities were probably related to the strong absorption abilities of the N-TiO2-x%WO3.