Neutron diffraction and calorimetric study on Al-based metallic glasses

The kinetics of transformation of the melt spun Al87Ni7Nd3Cu3 alloy was ana lysed by differential scanning calorimetry (DSC) and neutron diffraction (N D) experiments. The study of the emerging nanocrystalline grained structure by in situ heat treatment on quenched ribbons of the aluminium rich alloy composition indicates that no detectable nanocrystallisation occurs till te mperatures of about 370 K. Changes of the structure occur in two well defin ed and not overlapped temperature ranges. The thermodynamic optimisation of the Al-rich part of the Al-Ni-Nd-Cu system, by computing calculation of th e equilibrium and metastable phase diagrams, is applied to the kinetics of the crystallisation of the face-centered-cubic (fcc)-(Al) for the Al87Ni7Nd 3CU3 alloy. The fcc-(Al) precipitation occurs in a temperature interval of similar to 200 K, although the most rapid structural changes occur at tempe ratures around 380 K. These results are indicative of the diffusion control of the last stages of the first crystallisation event. Eutectic precipitat ion of fcc-(Al) + Al3Ni is promoted when temperature is about 520 K. The ov erall analysis shows that primary fcc-(Al) crystallisation is kinetically h idden. (C) 2001 Elsevier Science B.V. All rights reserved.