THE AMORPHOUS METALLIC AL91LA5NI4 ALLOY - KINETICS OF CRYSTALLIZATION

Crystallization of an amorphous ternary alloy with high aluminium cont ent (Al91La5Ni4) was investigated. Crystallization begins with precipi tation of alpha-Al (T-x = 313 K, reaction enthalpy Delta H-1 = 1.4 kJ/ mol), controlled by La diffusion. The diffusivity of La was estimated at 523 K as (8.8 +/- 1.6) . 10(-21) m(2)/s. At higher temperatures, Al 11La3 and Al3Ni are being formed by eutectic reaction (Delta H-2 = 2.4 kJ/mol, reaction exponent 3.5 to 4). The activation energies for the eutectic reaction were obtained in isothermal (237 +/- 8 kJ/mol) and i n continuous heating conditions (229 +/- 7 kJ/mol). The degree of crys tallinity of the specimens is related to their hardness. The partial c rystallization of alpha-Al nanoparticles (up to 30 vol.%) enhances the alloy's hardness without significant loss of ductility.