Stress Corrosion Cracking of Ultrafine-Grained Ti-2Fe-0.1B Alloying after Equal Channel Angular Pressing

In the present study, the stress corrosion cracking (SCC) of ultrafine-grained (UFG) Ti-2Fe-0.1B prepared by equal channel angular pressing (ECAP) was investigated by a slow strain rate test (SSRT) with in-site electrochemical equipment. In comparison with the atmosphere, results indicated that the mechanical properties of Ti-2Fe-0.1B alloy degraded in the simulated sea water, and the SCC sensitivity of UFG Ti-2Fe-0.1B alloy is much lower than the initial coarse-grained (CG) state. The enhanced SCC resistance of UFG Ti-2Fe-0.1B alloy could be attributed to the mechanical and corrosive aspects simultaneously. First of all, the strength of UFG Ti-2Fe-0.1B alloy is much higher than the CG state, but the elongation to failure of UFG Ti-2Fe-0.1B alloy decreased more than 1.8 times. The UFG sample suffered crack initiation until failure with a relative short time and low plastic deformation, which weakened the effect of corrosion during SSRT. In addition, X-ray photoelectron spectroscopy (XPS) revealed that the thickness of the passivation film of the UFG Ti-2Fe-0.1B alloy is thicker and that the component of the passivation film possesses a higher proportion of TiO2 in the same etched depth, which is beneficial to the corrosion resistance. Furthermore, according to the in-site electrochemical experiment curves, it is believed that the passivation film has a higher repair ability after cracking during SSRT for the UFG Ti-2Fe-0.1B alloy due to the decrease in grain size and the increase in dislocation density.