Effects of hot-pack rolling process on microstructure, high-temperature tensile properties, and deformation mechanisms in hot-pack rolled thin Ti–44Al–5Nb-(Mo, V, B) sheets

Abstract

Thin Ti–44Al–5Nb–1Mo–2V-0.2B alloy sheets were processed under different pack-rolling process directly from HIPed ingot in (α+β) phase region. The corresponding microstructure evolution, deformation mechanisms, and high-temperature tensile properties were systematically studied. As the pack-rolling progressed and thickness of plates is reduced, the microstructure was characterized by elongated lamellar colonies with B2+equiaxed γ grains at colony boundaries, that transformed into nano-lamella colonies along with γ platelets within B2 grains. The nano-lamella colonies were divided by a number of α mechanical twins and deformation bands. During the initial stage of rolling, mechanical twins, continuous, and discontinuous dynamic recrystallization of γ were the primary deformation mechanisms in the multi-phase microstructure. When the total rolling reduction was 74%, α2 phase dominated the deformation instead of γ. Two kinds of straight HAGBs with ~60.6° - 65.5° and ~71.0° - 72.7° formed in pairs in α2 colonies indicating the presence of twin boundaries and shear bands, respectively. While both the as-rolled alloys were produced via 4 and 6 rolling passes, exhibited high performance at 800 °C with ultimate tensile stress and ductility of ~600 MPa and 60%–70%, respectively. Nano-lamellae, nanoscale DRX grains, and ω precipitation in B2 grains at colony boundaries contributed positively to the high-temperature tensile properties.