Influence of Pre-deformation on Phase Transformations and Microstructures in Near β Ti Alloy During Aging

The influence of pre-deformation on phase transformations, microstructures and hardening response in near /3 Ti alloy Ti5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe (wt%) during aging treatment was studied. The results show that obvious alpha phase refinement and stronger age hardening effect can be achieved when the alloy is slightly deformed before aging treatment. Because the formation of intermediate phases (O ', omega and O '') suppresses long-range stress induced martensitic transformation and mechanical twinning, the alloy is mainly deformed via dislocation slipping during loading. Large numbers of crystal defects are generated during pre- deformation. With increasing the pre-deformation, the number density of dislocations increases gradually. These crystal defects generated by pre-deformation may partly annihilate upon early aging, but the precipitation of alpha can also be promoted, resulting in refined alpha precipitates. In the sample with 5% pre-strain, the average thickness of alpha precipitates decreases by 57% after aging at 600 degrees C compared with the sample without pre-strain, and the number density increases from 7.0 +/- 1 laths/mu m2 to 22.0 +/- 3 laths/mu m2. Some platelet-shaped alpha phases form when the samples experience comparably large pre-strains such as 12% and 20%. It proves that the refined alpha precipitates and better hardening effect can be achieved by pre-deformation plus aging treatment for titanium alloy.