EVOLUTION OF MICROSTRUCTURE IN CO-CU MULTILAYERS DURING THERMAL ANNEALING

The microstructure evolution of Co-Cu multilayered films with two comp ositions was studied by in-situ annealing in transmission electron mic roscopy (TEM). Interestingly, a new metastable crystalline (KY) phase of f.c.c. structure with a = 3.58 Angstrom was formed in a Co26Cu74 sa mple, grew up with increasing temperature and transformed to a perfect single crystal at 600 degrees C. The amorphous phase formed by anneal ing at 700 degrees C for 30 min. In addition, this MX phase and Co pha se with h.c.p. structure were observed in a Co52Cu48 sample and were q uite stable under thermal annealing up to 700 degrees C. A Gibbs free- energy diagram was constructed by calculating the free energies of the amorphous phase and of the as-deposited Co-Cu multilayers, to which t he interfacial free energy was added. A relevant interpretation of the observed behaviour was proposed.