Tensile behavior at 700 °C in Ti-Al-Sn-Zr-Mo-Nb-W-Si alloy with a bi-modal microstructure

The effect of lamellar α phase (αL) thickness on tensile behavior at 700 °C of BTi-6431S titanium alloy is investigated. Two types of bi-modal microstructures are introduced through different heat treatments. Both of them have similar volume fraction of equiaxed α phases (αe). One has thick α lamella named BTL, and another has fine α lamella named BFL. The results show that dynamic recrystallization (DRX) happens in the α phase during tensile process at 700 °C. After being deformed at 700 °C, the shape of αL in BFL and BTL transforms into sphere. BFL possesses higher tensile strength, and the elongation is twice as large as BTL at 700 °C. Compared to the thick αL, the fine αL has more excellent accommodative deformation capability. There are cracks found to be of wedge type located at the grain triple junctions in both BFL and BTL. In addition, some small voids stay at the lamellar boundaries in BTL. In order to acquire a good combination of tensile strength and elongation at 700 °C for BTi-6431S alloy, the thickness of αL should be reduced.