Influence of additive element on surface oxide film of A356 alloy

The influences of RE-modification and Sr-modification on the hydrogen content and surface oxide film of A356 aluminum alloy melt were investigated. The hydrogen content of the melt was measured by reduce pressure test. The phases in the surface oxide film were analyzed by X-ray diffractometry (XRD), and the morphology of the surface oxide film was observed by scanning electronic microscopy (SEM). The results show that RE-modification reduces the hydrogen content of A356 aluminum alloy greatly. Contrarily, Sr-modification increases the hydrogen content remarkably. After being treated with RE, a large number of LaAl11O18 consisting of Al2O3 and La2O3, are generated in the surface oxide film of A356 alloy. The surface oxide film of Sr-modification is almost composed of Al2SrO4. According to the results of SEM, the surface oxide film of Sr-modification is very easy to crack, destroy the continuity and compactness of surface oxide film, accelerate the vapor diffusing into the melt, consequently, increase the hydrogen content of A356 alloy melt significantly. But RE-modification makes the surface oxide film compact, and restrains the aluminum exposed to water, so reduces the hydrogen content of A356 alloy melt.

Effect of depressurizing speed on mold filling behavior and entrainment of oxide film in vacuum suction casting of A356 alloy

The effect of depressurizing speed on mold filling behavior and entrainment of oxide film of A356 alloy was studied. Themold filling behavior and velocity fields were recorded by water simulation with particle image velocimetry. The results show thatthe gate velocity first increased dramatically, then changed with the depressurizing speed: the gate velocity increased slowly atrelatively high depressurizing speed; at reasonable depressurizing speed, the gate velocity kept unchanged; while at lowerdepressurizing speed, the gate velocity decreased firstly and then kept unchanged. High gate velocity results in melt falling backunder gravity at higher speed. The falling velocity is the main factor of oxide film entrainment in vacuum suction casting. The designcriterion of depressurizing rate was deduced, and the A356 alloy castings were poured to test the formula. The four-point bend testand Weibull probability plots were applied to assessing the fracture mechanisms of the as-cast A356 alloy. The results illuminate amethod on designing suitable depressurizing speed for mold filling in vacuum suction casting.

Surface characteristics and structure of oxide films containing Ca and P on Ti substrate

The oxide films were obtained in an electrolyte of calcium glycerphosphate (Ca-GP) and calcium acetate (CA) by microarc oxidation (MAO). The oxide films displayed a porous and rough structure on the film surface, and the roughness tended to increase with increasing voltage of microarc oxidation. The oxide film exhibited a uniform coating and tends to be well boned to the substrate. The thickness of oxide films depended on the final voltage at a constant concentration of electrolyte solution. Ca and P were also incorporated into the oxide film during the microarc oxidation process. It was found that the electrolyte of calcium glycerphosphate (Ca-GP) and calcium acetate (CA) was suitable for microarc oxidation to form oxide film containing Ca and P on Ti substrate. The concentration of Ca and P were 11.6 at% and 6.4 at%, respectively, when microarc oxidation was performed in the electrolyte of 0.06 M Ca-GP and 0.25 M CA at current density 50 A/m^2 and final voltage 350 V. The composition of the Ca, P and Ti changed during depth profiling. The crystalline phases were only anatase when final voltage was below 300 V and rutile was presented when voltage was up to 350 V. The microstructure, phase structure and phase composition were investigated by scanning electron microscopy (SEM), atomic force microscope (AFM), energy dispersive X-ray microanalyser (EDX), and X-ray diffraction (XRD).

Fabrication of nanoporous TiO_2 films with novel surface morphology on conducting glass(FTO) substrate

The crystalline structure and surface morphology of TiO2 semiconductor coating play an important role in the conversion efficiency of dye-sensitized solar cells. In order to obtain TiO2 coating with controllable morphology and high porosity, nanoporous TiO2 films were fabricated on conducting glass （FTO） substrates, Ti thin films （1.5-2 gin） were deposited on conducting glass （FTO） substrates via the DC sputtering method, and then electrochemically anodized in NH4F/ethylene glycol solution. The crystalline structure and surface morphology of the samples were characterized by X-ray diffraction （XRD） and field emission scanning electron microscopy （FESEM）, respectively. The influences of anodizing potential, electrolyte composition, and pH value on the surface morphology of nanoporous TiO2 films were extensively studied. The growth mechanism of nanoporous TiO2 films was discussed by current density variations with anodizing time. The results demonstrate that nanoporous TiO2 films with high porosity and three-dimensional （3D） networks are observed at 30 V, when the NH4F concentration in ethylene glycol solution is 0.3% （mass fraction） and the electrolyte pH value is 5.0.

The Effects of Annealing on the Surface Properties of Titania Films Prepared on Titanium by Micro-Arc Oxidation

Titanium and its alloys are widely used in the aerospace, marine, and biomedical industry due to their unique bulk properties such as high strength-to-weight ratio and melting temperature, good corrosion resistance, and favorable biocom- patibility. However, in some applications, com- ponents made of titanium or titanium alloys exhibit poor wear resistance under stationary or dynamic loading as well as contact corrosion manifested by the relatively negative standard electrode potential （-1.63 V ） . In order to improve the surface properties of titanium and its alloys, several techniques such as PVD （ physical vapor deposition ） /CVD （chemical vapor deposition ） coatings,

In vitro and in vivo evaluation of porous NiTi alloy modified by sputtering a surface TiO_2 film

A uniform and dense TiO2 film was grown on the surface of porous NiTi shape memory alloys(SMAs) successfully by RF magnetron sputtering.The morphology and composition of the surface film were analyzed by using scanning electron microscopy and X-ray photoelectron spectroscopy.The corrosion resistance measurement proved that the surface modified porous NiTi SMAs exhibit better corrosion resistance and over 25% reduction of Ni ion release in the blood of the rabbits in comparing with the samples without surface modification.Moreover,the biocompatibility,as demonstrated by cell adherence and implant surgery,revealed that the cell adherence and bone tissue inducing capability are respectively enhanced over 1.1-1.2 and 9-10 times by sputtering a uniform TiO2 film on the surfaces of porous NiTi SMAs.