Study of hydrogen embrittlement behavior and mechanism of Ti-2.5Al-2Zr-1Fe by slow strain rate method
Authors: Zhao You-Peng , Liu Xiao-Yong , Liu Hui , Fang Kun , Wang Jia , Luo Xian-Fu , Xu Ning , Sun Xu-Lu , Liu Yu , Gao Yu-Hao , Wu Ze-Peng , Li Xue-Feng , Zhang Xin-Yao ,   National Key Laboratory of Marine Corrosion and Protection, Luoyang Ship Material Research Institute, Luoyang 471023, China
Published: September 2024

The Ti-2.5Al-2Zr-1Fe used as hull structural material, is susceptible to hydrogen embrittlement induced by corrosion and hydrogen evolution in marine environments. Considering the long-term service of ships, the hydrogen embrittlement behavior under slow strain rate is crucial for evaluating the alloy’s service performance and ensuring long-term ship structural safety. In order to investigate the hydrogen embrittlement mechanism of Ti-2.5Al-2Zr-1Fe alloy under slow strain rate conditions, this study combines slow tension and constant displacement loading techniques to systematically evaluate the attenuation of mechanical properties and the dynamic changes in hydrogen embrittlement sensitivity of hydrogen-containing Ti-2.5Al-2Zr-1Fe alloy. Employing scanning electron microscopy (SEM), we thoroughly analyze the microstructural features of fracture surfaces. Meanwhile, the close correlation between the brittle zone at the fracture site and the macroscopic distribution of hydrogen atoms is elucidated by using secondary ion mass spectrometry (SIMS). Additionally, theoretical analysis based on diffusion equations reveals a notable increase in hydrogen diffusion distance within the Ti-2.5Al-2Zr-1Fe alloy as hydrogen charging time increases. Further, using the dislocation-hydrogen interaction model, we derive a critical strain rate threshold <inline-formula><tex-math id="M1">\begin{document}$ {\varepsilon _0} = {{\left( {30RT} \right)} {/ } {\left( {\rho DE} \right)}} $\end{document}</tex-math></inline-formula> for dislocation-mediated hydrogen transport in titanium alloys. When the externally applied strain rate <i>ε</i> falls below this threshold, dislocations efficiently capture and transport hydrogen atoms, enhancing hydrogen diffusion depth and significantly augmenting the alloy’s hydrogen embrittlement sensitivity, thereby accelerating material embrittlement. The Vickers-hardness (HV) test further elucidates the dual nature of hydrogen’s influence on titanium alloy properties: although moderate hydrogen content slightly enhances surface hardness, exceeding a specific threshold leads to a major negative influence on plasticity, far exceeding the benefits of surface hardening, resulting in a substantial decline in overall mechanical performance. To comprehensively decipher the hydrogen embrittlement mechanism of Ti-2.5Al-2Zr-1Fe alloy, transmission electron microscopy (TEM) is employed to analyze the phase composition in regions of high hydrogen concentration, crack tips, and their vicinities. The analysis results indicate that no direct precipitation of hydrides is observed; instead, hydrogen atoms preferentially accumulate in the <i>β</i>-phase, prompting microcrack propagation along <i>β</i>-phase boundaries. According to the aforementioned experimental data and microstructural analysis, we propose that the hydrogen embrittlement mechanism in Ti-2.5Al-2Zr-1Fe alloy is primarily governed by the HEDE mechanism. Furthermore, when the strain rate falls below <i>ε</i><sub>0</sub>, it synergizes with the dislocation-mediated hydrogen transport mechanism, vastly expanding the influence scope of the HEDE mechanism and exacerbating the alloy’s hydrogen embrittlement sensitivity.