Crystallization Behavior and Microhardness Evolution in Al_92−xNi₈La_x Amorphous Alloys

The crystallization behavior of melt-spun amorphous Al_92−xNi₈La_x (x = 4 to 6) alloys was investigated by means of differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Crystallization kinetics were analyzed by Kissinger and Johnson–Mehl–Avrami approaches. Microhardness of all the ribbons was examined at different temperatures and correlated with the corresponding structural evolution. The results show that the variation of La content from Al₈₈Ni₈La₄ to Al₈₆Ni₈La₆ has significant influence on the crystallization pathways from amorphous to stable crystalline phases and on the evolution of microhardness with temperature. The two stages of crystallization in Al₈₈Ni₈La₄ and Al₈₇Ni₈La₅ alloys correspond to formation of fcc-Al and Al₁₁La₃, Al₃Ni, Al₃La. In Al₈₆Ni₈La₆, three stages of crystallization are observed which correspond to formation of a metastable phase, fcc-Al, Al₁₁La₃, Al₃Ni, and Al₁₁La₃, Al₃Ni, Al₃La, and decomposition of a metastable phases to stable crystalline phases.