Microstructure of the Directional Solidified Ti-45Al-7Nb Alloy

By the liquid metal cooling method, the microstructure character of directional solidification of Ti-45Al-7Nb (at%) alloy was examined. The results show that both the solidification behavior and lamellar orientations are affected by withdrawing rate. The primary phase is alpha phase, and lamellar orientation is perpendicular to the growth direction at the withdrawing rate of 0.36 mm/min. The primary phase converts into beta phase at the withdrawing rate of 1 similar to 10 mm/min, alloy solidify completely into the beta phase field, and lamellar orientation tends to parallel or incline with the angle of 45 degrees to the growth direction. When the withdrawing rate increases to 20 mm/min, the primary is also beta-phase, followed by the peritectic reaction of L + beta ->alpha, and lamellar orientation is inclined with the angle of 45 degrees similar to 75 degrees to the withdrawing direction.