Phase transformation behavior of Ti–40Al–8Nb alloys with a submicron (ω0+γ) microstructure during tempering at 1000 °C

In this work, the phase transformation behavior of Ti–40Al–8Nb (at. %) alloys with a submicron (ω0+γ) microstructure during tempering at 1000 °C was investigated, and special attention was paid on the ω0-assisted α2 nucleation. Results indicated that the ω0+γ→B2→α2 transformation dominated the precipitation of α2 phase. The ω0 and γ phases first dissolved into the B2 phase within a short time, and then the B2→α2 transformation occurred. The α2 phase could nucleate in the interior of B2 matrix and precipitate at the B2/γ interfaces by following the Burgers orientation relationships (ORs), <11–20>α2//<111>B2 and (0001)α2//{110}B2. With the increase of isothermal holding time, the γ phase reprecipitated through two phase transition routes, including B2→γ and α2→γ transformations by following the Kurdjumov-Sachs ORs, <111>B2//<110>γ and {110}B2//{111}γ, and Blackburn ORs, i.e., (0001)α2//{111}γ and <11–20>α2//<011>γ, respectively. Finally, a (α2+γ+B2) microstructure was obtained after isothermal holding at 1000 °C for 300 min.