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

Ti-50.8% Al has been cast using unidirectional solidification to produ ce specimens with a highly directional structure. Each specimen consis ted of the intermetallic phases, TiAl and Ti3Al. Both phases existed a s 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 ex amining the microstructure. Deformation revealed a highly anisotropic structure since ductility depended upon the principal direction of sli p. Poor slip, occurring in a direction through the lamellae, was attri buted to the Ti3Al phase where cracking initiated. Heating at 1200-deg rees-C resulted in recrystallization of the TiAl phase. The recrystall ization started at the ends of the specimens as a result of residual m echanical damage, before spreading along individual lamellae into the bulk.