Effect of Drawing Velocity on Structure of Directionally Solidified Ti-48Al-8Nb Alloy

The directionally solidified samples of Ti-48Al-6Nb-1Cr alloys were successfully prepared by a resistance furnace directionally solidified apparatus.The effects of different drawing velocities on the structure of liquid-solid interface and the structures of the transition zone and steady state zone were observed.The interface morphologies were observed as cellular dendrites at 5 μm/s drawing rate and fully-developed dendritic interface at 25 μm/s.The results show that the angle between lamellar(γ+α2) orientation and growth direction lay exhibited almost 45° at 5 μm/s,which shows the leading phase growth in microstructures is β phase.However when the drawing rate is 25 μm/s,the propotion of α2/γ lamellar perpendicular to the growth direction increases,the lamellar orientation is 0° and 45° on the transition zone and the angle reaches 90° on the steady state zone,the leading phase changes into α phase.When the drawing rate is 50 μm/s,the leading phase is almost α phase.The secondary dendrite arm spacing and the interlamellar spacing decreases with the increase of drawing velocity.