Kinetic Aspects of the Nanocrystallization and Evolution of Microhardness in Al92-XNi8LaX Amorphous Alloys

Marginal glass forming Al-based alloys have attracted considerable attention due to the occurrence of a primary crystallization reaction that yields a microstructure consisting of uniformly dispersed Al-nanocrystals embedded in an amorphous matrix. Rapidly solidified Al-alloys ribbons containing 8 at.% Ni and 4-6 at.% La were prepared by single roller melt-spinning technique. As-melt-spun and annealed ribbons were investigated by means of differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and hardness measurements. XRD studies revealed that ribbons are fully amorphous in the as-melt-spun state. DSC studies showed that crystallization proceeds in two or three stages that are sensitively influenced by La content. Crystallizations kinetics were analysed by Kissinger and Johnson-Mehl-Avrami approaches. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding structural evolution.