Huiping Tang

Highly Ordered Coaxial Bimodal Nanotube Arrays Prepared by Self-Organizing Anodization on Ti Alloy†

The fabrication of nanomaterials with well-ordered complex structures is one of the most important issues among advanced materials sciences, not only due to their potential applications, such as information-storage devices, microelectronics, and biosensors, but also due to their high technological impact. Electrochemical self-organization is an efficient approach towards building microblocks and nanoblocks into highly ordered macroscopic materials, which can be observed in deposition or dissolution reactions. In the past few years, highly ordered, vertically oriented tubular or porous nanostructures have been fabricated by simple anodization on Si, Al, Ti, and some other alloys. A method that provides control of the architecture of titania nanotube arrays is particularly desirable because, when such arrays are highly ordered, they possess many interesting properties. To date, the microstructure, diameter, and length of such oxide nanotubes in highly ordered arrays has been controlled by varying anodization parameters including the applied potential, concentration, pH value of electrolytes, anodization time, and suitable co-operation of alloying elements. TiO2 nanotube arrays have been the subject of extensive investigations to realize heteroatomic nanotubes, for example, Ti Nb O, Ti Al O, and Ti Fe O nanotube arrays. In the past few decades, progress has been made in fabricating coaxial nanotubular structures by filling the hollow cavities of nanotubes with nanorods, which may be shielded

Microstructure and fracture toughness of a TiAl-Nb composite consolidated by spark plasma sintering

Abstract A TiAl-Nb composite was prepared by spark plasma sintering (SPS) at 1250 °C and 50 MPa for 5 min from prealloyed TiAl powder and elemental Nb powder in a molar ratio of 9:1 for improving the fracture toughness of TiAl alloy at room temperature. The microstructure, phase constitute, fracture surface and fracture toughness were determined by X-ray diffractometry, electron probe micro-analysis, scanning and transmission electron microscopy and mechanical testing. The results show that the sintered samples mainly consist of γ phase, O phase, niobium solid solution (Nbss) phase and B2 phase. The fracture toughness is as high as 28.7 MPa·m1/2 at room temperature. The ductile Nbss phase plays an important role in absorbing the fracture energy in front of the cracks. Moreover, B2 phase can branch the propagation of the cracks. The microhardness of each phase of the composite was also tested.

Microstructure and tensile properties of containerless near-isothermally forged TiAl alloys

Abstract Ti–47Al–2Nb–2Cr–0.4(W, Mo) (mole fraction, %) alloy ingot fabricated using vacuum consumable melting was containerless near-isothermally forged, and the high temperature forgeability, microstructure and tensile properties were investigated. The results show that the TiAl ingot exhibits good heat workability during containerless near-isothermally forging process, and there are not evident cracks on the surface of as-forged TiAl pancake with a total deformation degree of 60%. The microstructure of the TiAl ingot appears to be typical nearly-lamellar(NL), comprising a great amount of lamellar colonies (α 2 +γ) and a few equiaxed γ grains. After near-isothermally forging, the as-forged pancake shows primarily fine equiaxed γ grains with an average grain size of 20 μm and some broken lamellar pieces, and some bent lamellas still exist in the hard-deformation zone. Tensile tests at room temperature show that ultimate tensile strength increases from 433 MPa to 573 MPa after forging due to grain refinement effect.

Fabrication of multilayer Nb2O5 nanoporous film by anodization of niobium foils

Multilayer Nb2O5 nanoporous films were successfully synthesized on Nb surfaces by the control anodization process in ethylene glycol containing 4xa0vol% HF and 2xa0vol% H2O2 electrolyte. The nanoporous films are characterized in detail by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The Nb2O5 nanoporous films have a multilayer morphology with the side wall thickness of ~5xa0nm, irregular pores with a diameter of ~25xa0nm, and a length of up to 7.39xa0μm, depending on the anodization time. A mechanism for the multilayer Nb2O5 nanoporous formation was also discussed. These nanoporous materials can be very useful in the fields of solar cells, gas sensors, catalysts, optical filters, and capacitors.

Fabrication, characterization and biocompatibility of TiO2 nanotubes via anodization of Ti6Al7Nb

Abstract Ti6Al7Nb has been used as an implant material because of its good corrosion resistance and high mechanical properties. However, the presence of aluminium (Al), which may lead to ostemalacia, anaemia and nervous system disorders, limited its wide clinical use. In this study, a titanium oxide (TiO2) nanoporous layer was fabricated on a Ti6Al7Nb alloy using an electrochemical anodic oxidation method. The structure of the TiO2 nanoporous layer was examined by scanning electron microscopy. The chemical compositions of the samples were analysed by X-ray photoelectron spectroscopy (XPS). Biocompatibility was evaluated by culturing rat osteoblast cells. The result showed that TiO2 nanoporous layers comprise a mixed oxide containing TiO2 and a small amount of nobium oxides (Nb2O5) and almost no elemental aluminium. The outer layer of the TiO2 nanoporous layer comprises highly ordered nanotubes and the inner layer forms disordered nanopores. The TiO2 nanoporous layer could support the adhesion, proliferation, differentiation and gene expression of osteoblast cells. Therefore, a TiO2 nanoporous layer could enhance the biocompatibility of Ti6Al7Nb alloy and is as a promising candidate for Ti6Al7Nb alloy implants.