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 con ventional 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 consti tuent phase, including B-2, alpha (2), O phases. This study indicated that substitution of Nb with Ta improved the B2 transus temperature. Heat treatm ents in different phase fields produced different microstructures. It was d ifficult to remove the prior large B2 grain boundary when solid soluted abo ve B2 transus temperature. In order to optimize the microstructure, a compl ex processing method was proposed: prior heat treatment was applied to obta in a fine and homogenous Of B2 lath structure, followed by thermomechanical processing at suitable temperature. By means of this method, duplex micros tructure with equiaxed alpha (2)/O particles and fine O phase laths in B2 m atrix, and without prior large B2 grain boundary, was secured. A systematic means of microstructure controlling was suggested. (C) 2001 Elsevier Scien ce B.V. All rights reserved.