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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. Given the long-term service of ships, the hydrogen embrittlement behavior under slow strain rate is crucial for assessing the alloy's service performance and ensuring long-term ship structural safety. To investigate the hydrogen embrittlement mechanism of Ti-2.5Al-2Zr-1Fe alloy under slow strain rate conditions, this study integrated the use of 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 conducted a thorough analysis of the microstructural features of fracture surfaces. Simultaneously, Secondary Ion Mass Spectrometry (SIMS) was utilized to elucidate the intimate correlation between the brittle zones at fracture sites and the macroscopic distribution of hydrogen. Additionally, theoretical analysis based on diffusion equations revealed a notable increase in hydrogen diffusion distance within the Ti-2.5Al-2Zr-1Fe alloy as hydrogen charging time increased.Further, leveraging the dislocation-hydrogen interaction model, we derived a critical strain rate threshold ε0 = [(30RT)/(ρDE)] for dislocation-mediated hydrogen transport in titanium alloys. When the externally applied strain rate ε 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.Vickers Hardness (HV) testing further illuminated the dual nature of hydrogen's influence on titanium alloy properties: while moderate hydrogen content slightly enhances surface hardness, exceeding a specific threshold leads to a dominant negative impact on plasticity, vastly outweighing the benefits of surface hardening and 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) was 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 was observed; instead, hydrogen preferentially accumulated in the β-phase, prompting microcrack propagation along β-phase boundaries.Based on 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 ε0, 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.
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Keywords:
- Titanium alloy /
- Hydrogen embrittlement /
- Slow strain rate /
- Hydride
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