PARTICLE-SIZE EFFECTS IN PRIMARY CRYSTALLIZATION OF AMORPHOUS AL-NI-YALLOYS

Primary crystallization of amorphous Al-Ni-Y alloys, giving a dispersi on of nanometre-scale alpha-Al crystallites in an amorphous matrix, is studied using isothermal and non-isothermal DSC, XRD and TEM. Isother mal anneals followed by temperature scans reveal the influence of chan ging composition on the stability of the remaining matrix. A significa nt limitation on crystal growth can be the approach to metastable equi librium with the amorphous matrix. In equilibrium, the Volume fraction crystallized is lower for smaller crystallites because of the influen ce of the interfacial energy through the Gibbs-Thomson effect. The cry stallite/matrix interfacial energy can be estimated from the dependenc e of equilibrium volume fraction on diameter. This dependence also giv es rise to significant heat release during crystallite coarsening, and this is revealed in the shape of DSC peaks. (C) 1997 Elsevier Science S.A.