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

Abstract

The plastic behaviour of single-phaseγ-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 theγ-based lamellar alloys. The present contribution accounts for an investigation of mechanical properties and microstructural organization conducted in Al-richγ-TiAl single crystals oriented to activate single slip. Three separate topics are addressed.

• (I) 1/2 〈110] ordinary dislocations after deformation between room temperature and 800°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 flow 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 L1₀ structure, and from the interaction of these with a short-range ordered (SRO) Ti₃Al₅ phase. Striations can serve to discuss the absence of slip localization and the properties of cross-slip.