Effect of lamellar α on the stress corrosion cracking of Ti-6Al-4 V alloy in simulated oilfield brine

Highlights: • The Widmanstätten sample exhibited the best resistance to SCC. • The large colony α and the thick of lamellar α can improve the SCC resistance of the alloy. • The mechanisms affect stress corrosion crack propagation were discussed. The stress corrosion cracking (SCC) behavior of Ti-6Al-4 V alloy with different lamellar α microstructures in simulated oilfield brine was investigated in this study. The SCC susceptibility of the Widmanstätten sample was 11.0%, lower than that of the bimodal and trimodal samples (19.9%, and 18.0%, respectively). In the Widmanstätten sample, the crack growth path transitioned from a zigzag to a linear path when the crack moved from one colony to another because of the sliding variations in the slip bands with different orientations. The decrease in a SCC resistance of bimodal and trimodal samples resulted from the decrease in α/β colony size. Owing to the larger thickness and different orientation of lamellar α, the trimodal sample exhibited a slightly higher SCC resistance and more circuitous crack propagation than that in the bimodal sample. The deflection angle of the crack increased with an increase in the angle between the slip system, and the favorable slip system was prismatic in three samples. It can be concluded that one of the strategies to improve the SCC and crack growth resistance of Ti-6Al-4 V alloy in oil field applications is to tailor the lamellar α microstructure with different orientations and larger α colonies.