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

In order to reduce the anisotropy of mechanical properties of a coilable thin sheet of (α+β)-type titanium alloy, Ti–4.5Al–2Mo–1.6V–0.5Fe–0.3Si–0.03C (Ti9), for use in aircraft applications, duplex heat treatments were examined. In each duplex heat treatment, the first heat treatment controls the volume fraction of the primary α phase and orientation of the acicular α phase in (α+β) two-phase area between the primary α grains, whereas the second heat treatment stabilizes the α and β phases. The microstructure of the Ti9 sheet after the duplex heat treatment was analyzed by optical microscopy, pole-figure measurement through X-ray diffraction, and electron backscatter diffraction. The mechanical properties of the duplex heat-treated Ti9 sheet were evaluated by tensile tests.