Microstructural evolution and tensile behavior of Ti2AlNb alloys based α2-phase decomposition

Abstract

The formation mechanism of the fine plate-like O-phases within α2-phases and tensile behavior of an isothermally forged Ti–22Al–25Nb (at%) orthorhombic alloy at 1040°C during heat treatment were investigated. The investigation indicated that the alloys were heat-treated in O+B2 phase region after α2+B2 phase region isothermally forging, the equiaxed α2-phase was not stable and decomposed into O+α2 phases. The α2 phases formed during isothermal forging process have higher concentration of Nb and begun to decompose during O+B2 phase region heat treatment. And then the α2 phases separated into Niobium-lean and Niobium-rich regions through the Niobium diffusion: α2→α2 (Nb-lean)+O (Nb-rich). Nb-rich regions with composition similar to Ti2AlNb transformed to the O-phase, while the Nb-lean regions remained untransformed and retained the α2-phase. The deformation behavior and fracture mechanism of Ti–22Al–25Nb alloy at room temperature were discussed. The deformation behavior and microstructural evolution of this alloy at different temperatures and stain rates were also investigated using uniaxial tensile test.