Anomalous yielding in the complex metallic alloy Al13Co4

The single crystal deformation behaviour of orthorhombic Al13Co4 has been studied below the brittle-ductile transition temperature observed in bulk material from room temperature to 600 °C, using indentation, microcompression and transmission electron microscopy. At room temperature, slip occurred most easily by dislocation motion on the (0 0 1)[0 1 0] slip system, as observed in the ductile regime at high temperatures. However, as the temperature was increased towards 600 °C, the slip pattern changed to one consisting of linear defects running perpendicular to the loading axis. Serrated flow was observed at all temperatures, although at 600 °C the magnitude of the serrations decreased. Anomalous yielding behaviour was also observed above 226 °C, where both the yield and the 2% flow stress increased with temperature, almost doubling between 226 and 600 °C. It has been suggested that this might arise due to the increasing stability of orthorhombic Al13Co4 with respect to the monoclinic form with increasing temperature. This is shown to be consistent with the theoretical predictions that exist.