The effects of hydrogen on fatigue crack growth behaviour of Ti–6Al–4V and Ti–4.5Al–3V–2Mo–2Fe alloys

The fatigue crack growth rates (FCGRs) of Ti–6Al–4V and Ti–4.5Al–3V–2Mo–2Fe alloys were determined in gaseous hydrogen, air, and a soft vacuum. In hydrogen and at a stress ratio of 0.1, the deflected crack path associated with the localized brittle fracture of the α-phase could account for the reduced FCGR of Ti–6Al–4V. At a higher stress ratio of 0.5, hydrogen embrittlement enhanced cracking and alleviated the effect of crack deflections in Ti–6Al–4V specimens, resulting in the FCGR in hydrogen similar to that in air. In contrast, the FCGR of Ti–4.5Al–3V–2Mo–2Fe was insensitive to both the environment and stress ratio.