GROWTH AND COARSENING OF CO-RICH PRECIPITATES IN DILUTE CU-CO ALLOYS

Magnetic measurements have been undertaken with some dilute Cu-base alloys containing 0.4, 0.5, 0.6 and 0.7 at.% Co, respectively. As the Co-rich precipitate particles exhibit a superparamagnetic behaviour, the average particle radius (r) and the particle density per unit volume (N) could be determined as a function of the annealing time t for annealing temperatures between 743 and 803 K. Different stages of the decomposition processes have been characterized through r and N. In order to measure r for the extremely fine particles, magnetization curves have been determined in the temperature range from 5 to 300 K. It has been shown that the temperature of measurement is important for the r and N values determined. The volume diffusion coefficients calculated as per the r2-t growth law in the present study are in good agreement with the relevant data in the literature. The nucleation rate is 5 . 10(17) m-3 s-1 and the incubation time is 720 s for Cu-0.5 at.% Co at 763 K.