Resisting room-temperature creep in titanium alloys by pre-compression

For deep-sea submersibles, the service life of titanium alloys in lightweight pressure hulls is dictated by room-temperature creep deformation. Under high stress in deep-sea, the mechanism for room-temperature creep is primarily dominated by dislocation slip in the soft grains. Guided by the principles of dislocation pile-up and back stress hardening, a pre-compression treatment was applied to Ti80 alloy. Via pre-compression, the dislocation density increased significantly by 1.9–2.5 times in some softer grains whereas the average dislocation density only experienced a 22 % increase. This treatment effectively elevated the critical resolved shear stress (CRSS) and enhanced the resistance to dislocation motion. Accordingly, the creep stress threshold is raised by at least 14 % and the total creep strain is reduced by 80 % after 1000 h of creep at 90 % the yield strength. A creep constitutive model based on back stress evolution was developed to accurately describe the creep behavior of Ti80 alloy. That model incorporates an estimation of the initial back stress induced by pre-compression treatment and its effect on dislocation slip. The results demonstrate crucial insights into the optimization of materials for deep-sea pressure hulls and their long-term performance prediction.