Effect of Secondary α Phase on Stress Corrosion Cracking of a Novel Metastable β Titanium Alloy in 3.5% NaCl Solution

The effect of the secondary α phase on stress corrosion cracking of a novel metastable β titanium alloy, Ti-6Mo-5V-3Al-2Fe, in 3.5% NaCl solution was investigated by slow strain rate testing. Fine acicular secondary α phase was obtained by aging at the low temperature of 520 °C, and coarsened rod-like secondary α phase was obtained by aging at the high temperature of 680 °C. The electrochemical measurement results and slow strain rate testing results show that the microstructure contained with fine acicular secondary α phase exhibits better corrosion resistance and less stress corrosion cracking susceptibility. The fracture morphology exhibits a mixed fracture characteristic with shallow and small dimples, as well as tear ridges and flat facets with undulating surfaces. The combination of Absorption Induced Dislocation Emission and Hydrogen Enhanced Localized Plasticity is the main mechanism for stress corrosion cracking. Fine acicular secondary α phase with narrow spacing leads to less accumulated dislocations and smaller localized stress, so that has a beneficial effect on stress corrosion performance.