The mechanism of aqueous stress-corrosion cracking of α + β titanium alloys

•Different dislocation types and densities were observed beneath pre-crack dimples and SCC facets due to absorbed hydrogen.•The absorbed hydrogen diffusion probably proceeds by pipe diffusion through the planar slip bands ahead of the SCC crack tip.•Absorption Induced Dislocation Emission and Hydrogen Enhanced Localized Plasticity are the SCC mechanism for α + β Ti alloys.

In a previous paper (Cao et al., 2017) [1], a transition in fracture mode in aqueous NaCl Stress-Corrosion Cracking (SCC) of Ti-8Al-1Mo-1 V was reported. This paper attempts to unravel the operating mechanism for SCC by dislocation analysis on the Focus Ion Beam (FIB) lift-out foils from pre-crack and the SCC regions. It is shown that both basal and slips are operative in the SCC region while the basal is the only activated system in the pre-crack region. Moreover, there is an increase in dislocation density in the SCC region compared to the pre-crack region. Based on these observations, combined Absorption Induced Dislocation Emission (AIDE) and Hydrogen Enhanced Localized Plasticity (HELP) is proposed to be the operating mechanisms for SCC in α+β titanium alloys.