Microstructures in Al-rich γ-TiAl strained in the domain of temperature of flow stress anomalies

The plastic behaviour of single-phase gamma-TiAl poses a certain number of fundamental problems as to the origin of the flow stress anomaly and to how this is related to dislocation properties. Understanding these questions is of significant interest in the investigations of flow stress anomalies in intermetallics and in other materials. Also, it may reveal useful in the study of the gamma-based lamellar alloys. The present contribution accounts for an investigation of mechanical properties and microstructural organization conducted in Al-rich gamma-TiAl single crystals oriented to activate single slip. Three separate topics are addressed. (1) 1/2 [110] ordinary dislocations after deformation between room temperature and 800 degrees C. The magnitude of the cusping appears to depend on the chronology of dislocation immobilization. The distribution of pinning points is analysed and the temperature dependence of their density confronted to that of the now stress. (II) The core structure of [011] dislocations. After deformation at room temperature, [011] dislocations are dissociated into two partials separated by a stacking fault. The role of temperature and possible transitions of the dissociation are addressed. (III) The observation and analysis of background striations which cover the thin foils entirely. The striations are shown to be a deformation by-product resulting from the passage of perfect dislocations of the L1(0) structure, and from the interaction of these with a short-range ordered (SRO) Ti,AZ phase. Striations can serve to discuss the absence of slip localization and the properties of cross-slip.