In situ precipitation of θ on A1 in the Al-Cu system

Abstract

Precipitation in the Cu-Al system can be in several forms, some of which, such as the θ ", θ', and θ phases of CuAl2, have been extensively investigated by both X-ray and TEM methods (see e.g. 1). In general, the precipitation sequence has been systematically controlled by ageing supersaturated solutions of Cu in Al for specific times at temperatures chosen to lie within the upper and lower solvus lines of the required phase. Specimens for TEM were then prepared by standard techniques. In cases where precipitation was carried out in situ, using a hot-stage in the TEM, nucleation at the foil surfaces has appeared to play a prominent role, and precipitation within the foil is, for the most part, suppressed. In this investigation an additional feature is incorported, namely surface diffusion of Cu into a pure Al film, which then leads to the formation of CuAl2 θ-phase precipitates.