In order to improve the functions of microarc oxidation (MAO) films, the current work investigated the effects of the laser surface melting (LSM) process on MAO films fabricated in different electrolytes. A series of processing experiments was carried out on the composite films. In detail, MAO films using aluminum (Al) and silicon (Si) electrolytes were prepared on a Ti–6Al–4V alloy surface and then treated by using the LSM process. At the same time, the properties of the films, such as phases and morphology, were characterized and analyzed by X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that moderate-intensity plasma was more easily obtained on the silicon MAO (Si-MAO) films than on the aluminum MAO (Al-MAO) ones. Similarly, a higher laser power was necessary to liquefy or gasify alumina (Al2O3). Compared with the defective structure of Al-MAO film after LSM, the structure of the Si-MAO film was almost free of defects. The film morphologies showed that an MAO film with low porosity and a smooth surface can be obtained after LSM treatment using proper parameters. In conclusion, the composite silicate system process using the silicon electrolyte had better modification performance.
In order to prepare functional films containing a predetermined ratio of calcium (Ca) and phosphorus (P) and guide the rational allocation of chemical reagents on a titanium (Ti) alloy surface, calcium/phosphorus biological films were fabricated by using the microarc oxidation (MAO) process. The films’ morphology and elemental composition were observed and analyzed. Moreover, a wear resistance test was performed on the film surface. The influence of different concentrations and calcium/phosphorus molar ratios of the films and the MAO system were researched. The effects of electrolyte concentration on the calcium/phosphorus molar ratio of the films were also investigated. The experimental results show that with an increase in electrolyte concentration, the calcium and phosphorus contents of the films all decreased, but the calcium/phosphorus ratio increased. Similarly, the values of the calcium/phosphorus molar ratio and the calcium and phosphorus contents in the films all became lower. Furthermore, a proper electrolyte concentration is helpful in improving the surface properties of the films. If preparation of a film with a certain calcium/phosphorus molar ratio is wanted, this certain ratio can determine the different electrolyte molar concentrations of calcium/phosphorus and it can roughly determine the ratio of the compound reagent and improve the test efficiency.
The fracture toughness of brittle biofilms prepared through the microarc oxidation process on the Ti–13Nb–13Zr alloy needs to be improved. The ultrasonic technology was successfully incorporated into the process. The indentation test and its analysis method were adopted to measure the film fracture toughness. The properties of the film such as surface morphology and phase composition were compared with those of a film prepared without using the ultrasonic technology, and the toughening factors were analyzed and a calculation model of fracture mechanics was established. The results show that the composite-process film has higher fracture toughness than the single-process film with a different film porosity, and the toughness of the former can reach 2·65 MPa m1/2 for higher duty cycles. Parts of titanium dioxide (TiO2) phase transformation toughening, reduction of the main-crack stress concentration by microcracks and the densification of the microstructure caused by ultrasonic cavitation effect are the main reasons that fracture toughness improved. Similar results for measurement and calculations obviously indicate the validity of the model. The composite process can achieve the purpose of toughening titanium alloy biofilms.
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