DEFORMATION-BEHAVIOR AND HIGH-TEMPERATURE STABILITY OF UNIDIRECTIONALLY SOLIDIFIED, TWIN PHASE TIAL

Ti-50.8% Al has been cast using unidirectional solidification to produce specimens with a highly directional structure. Each specimen consisted of the intermetallic phases, TiAl and Ti3Al. Both phases existed as single crystal lamellae which were parallel to each other throughout the specimen and aligned along specific crystallographic orientations. Mechanical properties were assessed by deforming specimens such that slip occurred in different directions relative to the lamellae. High-temperature stability was assessed by heating for various times and examining the microstructure. Deformation revealed a highly anisotropic structure since ductility depended upon the principal direction of slip. Poor slip, occurring in a direction through the lamellae, was attributed to the Ti3Al phase where cracking initiated. Heating at 1200-degrees-C resulted in recrystallization of the TiAl phase. The recrystallization started at the ends of the specimens as a result of residual mechanical damage, before spreading along individual lamellae into the bulk.