Thermal exposure induced α_2 + γ → B2(ω) and α_2 → B2(ω) phase transformations in a high Nb fully lamellar TiAl alloy

摘要

As-HIPped Ti-44Al-8Nb-1B was exposed to 700 ℃ air for up to 3000 h. It has been found that the β phase removed by hot isostatic pressing (HIPping) reforms as ordered B2 with ω phase during parallel decomposition of α_2 lamellae to α_2 + γ lamellae and perpendicular decomposition of single α_2 short sections, causing phase transformations of α_2 + γ → B2(ω) and α_2 → B2(ω).