Kinetics of Mg6Ni nanocrystallization in amorphous Mg83Ni17

A comprehensive crystallization kinetics study was carried out in order to understand the mechanism of formation of a Mg-rich nanocrystalline Mg6Ni phase in a metallic glass with similar overall composition, Mg83Ni17. Adequate description of the transformation kinetics was obtained by the JMKA equation with an integer Avrami exponent n = 4, associated with nucleation and three-dimensional linear growth crystallization mechanism. To study the nanocrystals growth mechanism separately a controlled heat treatment of the amorphous alloy was applied and thus a three-dimensional growth with a constant rate was obtained (n = 3) for the pre-annealed alloys. For all transformation curves the dependence of n on the degree of transformation a, n(a), was analyzed and the regions with constant n were defined. The correct separation of the processes of nucleation and crystal growth allowed reliable values for the activation energies of both nucleation and growth processes to be determined. 2008 Elsevier B.V. All rights reserved.