Microstructure controlling by heat treatment and complex processing for Ti2AlNb based alloys

The phase evolution and microstructure controlling process were studied for Ti2AlNb based alloys. Monolithic sheet materials were produced through conventional thermomechanical processing techniques comprising non-isothermal forging and pack rolling. Phase evolution studies showed that depending on the heat treatment schedule, Ti2AlNb based alloys may obtain various constituent phase, including B2, α2, O phases. This study indicated that substitution of Nb with Ta improved the B2 transus temperature. Heat treatments in different phase fields produced different microstructures. It was difficult to remove the prior large B2 grain boundary when solid soluted above B2 transus temperature. In order to optimize the microstructure, a complex processing method was proposed: prior heat treatment was applied to obtain a fine and homogenous O+B2 lath structure, followed by thermomechanical processing at suitable temperature. By means of this method, duplex microstructure with equiaxed α2/O particles and fine O phase laths in B2 matrix, and without prior large B2 grain boundary, was secured. A systematic means of microstructure controlling was suggested.