Interfacial structure of θ precipitates in Al5wt.%Cu alloys

Abstract

Standard transmission electron microscopy techniques are applied to the study of the interface between the f.c.c. aluminum matrix (κ) and the complex b.c.t. CuAl 2 (θ) precipitates. Interfacial structure is found to be prevalent on an interface which has often been considered to be incoherent. Both contrast experiments and hot-stage electron microscopy reveal that growth of the interface proceeds by the ledge mechanism. During the high temperature experiments the growth ledges assume a stable position in the thin film about which small fluctuations occur. Small changes in temperature cause these positions to become unstable. The density of positionally stable growth ledges increases with increasing severity of the quench.