Effect of microstructure on hydrogen charging behaviour and post-charging corrosion of TC4 Ti alloy

Abstract

In marine environments, TC4 titanium alloy is simultaneously subjected to hydrogen damage and Cl⁻-accelerated corrosion, limiting its service reliability. To address this issue, this study optimised heat treatment processes to obtain three typical microstructures (equiaxed, bimodal and lamellar) in TC4 titanium alloy. The effects of microstructural regulation on hydrogen damage and postcharging corrosion behaviour were systematically investigated via cathodic hydrogen charging experiments and electrochemical measurements. Results indicate that a TiO₂–TiH_1.971 hybrid film, which exhibited n-type semiconductor characteristics similar to the native TiO₂ passive film, formed on the hydrogen-charged surface. Among the three microstructures, the equiaxed microstructure experienced the most severe passive film degradation, accompanied by reduced TiO₂ retention, and the bimodal microstructure maintained a relatively intact surface layer. This difference was attributed to the β-phase fraction: the bimodal microstructure, with the highest β-phase content (22.9%), provided efficient hydrogen diffusion pathways and enhanced hydrogen storage capacity, promoting hydrogen dissolution within the matrix and thereby reducing hydrogen accumulation at the film–substrate interface. Consequently, the bimodal-structured alloy exhibited superior corrosion resistance in subsequent chloride-containing tests. By contrast, the equiaxed microstructure, with a low β-phase fraction (8.9%), showed limited hydrogen uptake and retention, which led to serious passive film breakdown and consequently poor corrosion performance.