Dependence of Macro- and Micro-Properties on α Plates in Ti-6Al-2Zr-1Mo-1V Alloy with Tri-Modal Microstructure

Tri-modal microstructure is often the target microstructure of titanium alloy components. In this study, the parameters, such as volume fraction, size of primary equiaxed alpha (alpha(p)), secondary lamellar alpha (alpha(s)) and thin alpha plates (alpha(t)) in tri-modal microstructure of Ti-6Al-2Zr-1Mo-1V alloy are adjusted by double heat treatment procedures. The properties of these constituent phases and their effect on the macro-properties are then investigated. The results show that the hardness of primary alpha (alpha(p)) varies slightly with heat treatment routes. The hardness of alpha plates region including alpha(s) and alpha(t) increases with increasing alpha(t) volume fraction and not with decreasing thickness of alpha(s) and alpha(t). Using volume average of the thickness of alpha(s) and alpha(t) as effective thickness (t(eff)), the hardness of alpha plates region and t(eff) follow the Hall-Petch relationship. Meanwhile, as alpha(t) volume fraction increases, colony structure of alpha(s) is gradually destroyed, which makes each alpha(s) have large deformation degree by multiple directions slip. When volume fraction ratio of alpha(p), alpha(s) and alpha(t) is about 1:1:1, alpha(p) and alpha(s) can undergo relatively large deformation and alpha(t) can contribute relatively large strength to the alloy and therefore the alloy has both good strength and ductility.