Reduction in anisotropy of mechanical properties of coilable (α+β)-type titanium alloy thin sheet through simple heat treatment for use in next-generation aircraft applications

The Ti9 sheet was heat treated to obtain two different types of microstructures. A microstructure consisting of acicular α phase in the β grains was obtained by a first heat treatment above the β transus (1273 K) followed by water quenching and a second heat treatment at 973 K. A microstructure consisting of equiaxed primary α grains and an (acicular α+β) two-phase area between the primary α grains was obtained by heating below the β transus (1123-1223 K) followed by water quenching and a second heat treatment at 973 K. The volume fraction of the primary α grains decreased and the volume fraction of the acicular α phase with 12 variants increased instead of increasing first heat-treatment temperature, suppressing the alignment of the c axis of the α lattice parallel to the transverse direction within the rolling plane (T-texture formation) as a result. Anisotropy of the tensile properties can be decreased by increasing the first heat-treatment temperature because the T texture was decreased.