On the duplex nature and dislocation structure of the massive Cu–Ga phase

The massive phase transformation which occurs in Cu–Ga alloys on quenching from the high temperature β-phase has been studied using the technique of electron microscopy. The transformed alloys consist of a fine lamellar structure of h.c.p. or h.c.p. plus f.c.c. phases. The lamellae are twisted with respect to one another along the close-packed planes and are grouped together into packets or blocks which are joined by sub-grain boundaries that are similarly twisted. In regions where the f.c.c. lamellae are dense, their presence can be easily demonstrated by selected area diffraction through characteristic diffraction spots of the f.c.c. structure. However, in regions where the f.c.c. lamellae are less dense, the f.c.c. diffraction spots are too weak to be detected. It then becomes necessary to make a detailed study of the diffraction contrast effects. From such an analysis it was found that the observed fringe effects could not be identified with the presence of stacking faults. An examination of the dislocation networks in the basal planes of the h.c.p. matrix has shown that all the dislocations are extended.