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 α, n(α), 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.