Microstructural evolution and formation mechanism of FCC titanium during heat treatment processing

The phase transformation of Ti–20Zr–6.5Al–4V alloy was studied during different heat treatment processes. Due to the addition of zirconium possessing the high-stacking-fault energy, a small amount of Ti underwent allotropic transformation from hcp-Ti to face-centered cubic (fcc) Ti during heat treatment. The alloy, which was subjected to solid solution treatment at 950 °C for 60 min and subsequent water quenched, underwent the following phase transformations: β → α + β (residual) + α″ + fcc phase. The fcc phase was also found in the subsequent aging process, and when aging temperature reached 700 °C, the fcc-Ti completely decomposed into hexagonal close-packed α phase. The transus temperature of fcc-Ti was between 650 °C and 700 °C. It was found that the mechanical properties of the alloy are remarkably dependent on fcc phase content.

► The alloy with ST underwent the transformations: β → α + β + α″ + fcc phase.
► The lattice parameter “a” of the fcc phase was about 0.4385 nm.
► After aging at 450 °C, the highest strength was attained about 1740 MPa.
► The transus temperature of fcc-Ti was between 650 °C and 700 °C.