Interaction of Al2O3 thin films deposited on nanocrystalline titanium with hydrogen

The aim of the present study is to investigate hydrogen permeation through an aluminium oxide coating Al2O3, which was deposited on the nanocrystalline titanium (NCTi) using two methods: deposition from a substrate saturated with hydrogen, and saturation of Al2O3/NCTi system from an ambient medium (electrolyte, gas, plasma). Films were deposited onto the surface of specimens by magnetron sputtering. While performing the deposition, hydrogen diffused throughout the depth of the film; however, diffusion was restricted to the area near the film-substrate interface, affecting less than 50% of the thickness of the film. Film-substrate interface is significantly broader (compared to the deposition on an unsaturated substrate), and metallic hydroxides are formed in the interface. Saturation of Al2O3/NC Ti system with hydrogen was performed using three methods: electrolytic method, saturation from the high-frequency discharge hydrogen plasma, and from hydrogen atmosphere at high temperature and pressure. The analysis of the saturation process shows that the Al2O3 coating can protect the metal surface from hydrogen permeation only in the case of its operation in the conditions of contact with aqueous solutions.