Nanocrystal development during primary crystallization of amorphous alloys

During primary crystallization of multicomponent amorphous alloys a high density of nanocrystals can develop at levels up to 10(23) m(-3) and volume fractions > 0.30. For Al-base amorphous alloys at high Al nanocrystal densities, diffusion field impingement develops quickly above the glass transition and provides for a kinetic stabilization. A kinetics analysis has been developed to account for nanocrystal growth with diffusion field impingement and unequal component diffusivities. The analysis together with a thermodynamic model of the f.c.c.-liquid phase equilibria for Al-Y-Fe was applied to model DSC exotherms corresponding to primary f.c.c. nanocrystal formation. From the kinetics analysis an estimate of the diffusion coefficient of yttrium in the liquid is obtained above the glass transition as 1.4 x 10(-17) m(2)/s. New alloying strategies are discussed based upon the implications of the kinetics analysis. (C) 1998 Acta Metallurgica Inc.