Metastable evaporated thin films of CuAg AND CoAu alloys-II kinetics of the transformations

Abstract

The kinetics of the two stages in the transformation of an amorphous vapor-quenched alloy to the equilibrium two-phase state are studied in detail. The first stage, which involves the crystallization of the amorphous phase, is interpreted in terms of the classical theory of nucleation and growth. For CoAu, the measured activation energy of 1.40 eV, is made up of a diffusion activation energy of 1.31 eV and a term W*/4 = 0.09 eV, where W* is the barrier height for nucleation at the transformation temperature (430°K). The corresponding numbers for CuAg are 1.20, 1.12 and 0.08 eV (at 370°K). With the aid of thermodynamic data for the CuAg system, a value of 115 ergs/cm2 for the surface energy of the amorphous-crystalline interface is obtained. This agrees with values derived from the solidification of small droplets. The second stage can be interpreted as a spinodal decomposition process. It shows very nearly first order reaction kinetics, with activation energies of 1.65 eV for CoAu and 1.43 eV for CuAg, and a frequency factor ν0 ~ 1012 sec-1. © 1967.