Roughening of film fabricated by ultrasonic microarc oxidation on Ti–13Nb–13Zr

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 m^1/2 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.