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

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.