Crystallization kinetics of an amorphous Al85Ni10Y2.5La2.5 alloy

Amorphous Al 85 Ni 10 Y 2.5 La 2.5 alloy powder with the particle size of −500 mesh was produced by gas atomization. Crystallization kinetics of the amorphous phase were studied using differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy. Crystallization occurred in the temperature range 230–450°C in three exothermic reaction steps. The onset and peak temperatures for these reactions shifted toward higher temperatures when the heating rate was increased; this allowed the activation energies of the mechanisms controlling each step of the crystallization to be determined as 148, 336, and 274 kJ/mol, respectively. XRD and SEM analysis of the powder heated to different temperatures showed that precipitation of Al-based particles occurred during the first exothermic reaction, crystallization of the Al 4 La phase and an increase in the volume fraction of the Al-based phase took place during the second exothermic reaction, and development of the Al 3 Ni phase occurred during the third exothermic reaction. After annealing at 550°C, the powder consisted of Al-based matrix reinforced with very fine intermetallic particles of different morphologies. The mechanism of crystallization is discussed.