The anomalous flow behavior in single-phase Ti44Al56 single crystals: The effect of deformation history

In this paper we present our studies of effect of deformation temperature on the anomalous flow behavior of [001] and [011] oriented Ti44Al56 single crystals grown in an ASGAL optical imaging floating zone crystal growth furnace. The specimens were compression tested at room temperature (RT), 973 and 1173 K and they displayed anomalous flow behavior. However, if the sample is deformed at high temperature, at about 973 K (below the peak temperature), and then retested at room temperature, the high temperature strength is retained, i.e. the flow stress is irreversible. But if the initial deformation at high temperature is performed at about 1173 K (above the peak temperature), and then deformed at room temperature the room temperature flow strength is observed, i.e. the flow stress is reversible. These results suggest that the reversibility of flow stress anomaly is determined by the deformation mechanism occurring at the elevated temperature. If the deformation mechanism at the two temperatures is the same, then the flow stress is irreversible, but if they are different, then it is reversible.