Microstructure optimization of ingot metallurgy TiAl

Two-step extrusion plus subsequent heat treatment have been applied to develop a fine-grained lamellar microstructure in a pilot ingot of Ti-46Al-2.5V-1.0Cr-0.3Ni (at.%) alloy. The cast lamellar microstructure was completely broken down to an equiaxed structure after the hot deformation with an accumulated extrusion ratio of 15:1 although the severe deformation produced unfavourable γ grain bands and very thin α2 plus β strips. In the following heat treatment, conditions have been optimized to obtain the desirable amount, morphology and distribution of the β phase at elevated temperatures. The final microstructure achieved mainly consisted of lamellar colonies with an average size of 65 μm and about 5 vol% of small B2 particles. Such a refined lamellar microstructure has shown remarkable strength retention and creep resistance at high temperatures while maintaining excellent ambient ductility and fracture resistance.