Effect of deformation of constituent phases on mechanical properties of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy

Deformation of constituent phases determines the mechanical properties of titanium alloys. To address this relationship, the deformation of primary α (αp), secondary α plates (αs) and residual β phase (βr) in Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy was investigated based on the microstructure near fracture surface of uniaxial tensile samples. It is found that αp is elongated and αs mainly undergoes kinking deformation during tensile tests. The deformation of αp is dominated by planar slipping, the deformation of αs in colony is dominated by planar slipping and in basket weave is controlled by twin, planar slipping and dislocation tangling and the deformation of βr is controlled by dislocation tangling. In the microstructure with high volume fraction of αp (about 60%), the deformation amount of both αp and αs increases with the thickness of αs, which increases the elongation of the alloy and changes the failure modes of αp from fracture to boundary separation. In the microstructure with low volume fraction of αp (19%) and long αs, αp has large deformation amount, while αs with relative small deformation amount has large kinking region which increases the strength of the alloy. However, due to low volume fraction of αp, its contribution to the ductility of alloy is limited and thus the elongation of the alloy is relatively small.