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.