As deep-sea exploration and oil and gas development continue to venture into deeper waters, titanium and titanium alloys, as the core materials for critical deep-sea equipment, are also facing severe tests in extreme environments. However, there has no systematic understanding from the atomic to the macroscopic scale for how static water pressure in deep sea affects the performance of titanium's surface passive film.
Recently, the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences has made an important breakthrough for this problem. By calculations and tests, the research team has systematically revealed the growth, evolution, and failure behavior of titanium's passive film under static water pressure for the first time.
The research has discovered the dual regulatory effect of static water pressure on the titanium passivation film: In the initial stage of passivation, the high-pressure environment promotes the inward diffusion of oxygen elements, accelerating the growth of the film layer and enhancing the initial protective ability; however, during long-term high-pressure service or when the film layer is damaged and needs repair, the pressure will induce local crystallization of the amorphous passivation film, forming a metastable TiO crystal phase. The resulting crystal boundaries become ion permeation channels, weakening the self-repair ability of the film layer and leading to a decline in corrosion resistance.
This research clarified the core mechanism of the "amorphous-crystalline" structural transformation and performance degradation of the passivation film, and identified that oxygen content and crystal phase structure are the key factors regulating the corrosion resistance of deep-sea titanium materials. This achievement provides theoretical support for the composition optimization and surface protection design of deep-sea titanium alloys, helps to more accurately assess the service life of deep-sea equipment materials, and promotes the technological upgrading of key deep-sea materials.