Optimization of Microstructure and Elimination of β(B2) Phase in As-Cast Ti-Al-Nb-W-B Alloy

The microstructures of as-cast Ti-Al-Nb-W-B alloy were investigated to assess the possibility of eliminating the triaxial beta(B-2) phase on the crystal boundary through heat treatment and multi-step forging thermal mechanical treatment. The microstructure evolution and growth mechanism were studied according to Ti-Al-Nb ternary phase diagram, and then the process of eliminating of the triaxial beta(B-2) phase on the crystal boundary was assessed. The results of the experiments indicate that the best way to eliminate beta(B-2) phase is holding at the 1260 degrees C for 8 h or 1220 degrees C for 36 h followed by furnace cooling, but the grains grow appreciably. On the other hand, after multi-step forging with a total deformation of more than 80%, the as-cast nearly lamellar structure can be refined obviously to the duplex microstructure, and the beta(B-2) phase is basically eliminated.