GENERAL EXISTENCE OF LEDGES ON ALPHA(1) PLATES IN CU-ZN-AL ALLOYS

A transmission electron microscopy (TEM) study was made of the interph ase boundary structure between the matrix and alpha(1) plates formed a t 250 degrees C, 300 degrees C, and 350 degrees C in three Cu-Zn-Al al loys. The experiments showed that the alpha(1) plates formed at each t emperature studied in all of the alloys are initially free of stacking faults. This observation, confirming the results of previous investig ations, shows that these plates cannot have formed by a shear mechanis m. Ledges were shown to exist on the broad faces and/or at the growth edges of the alpha(1) plates. Indirect evidence implies that the ledge s are mobile and that they can migrate along different directions on t he broad faces.