Particle-size effects in primary crystallization of amorphous Al-Ni-Y alloys

Primary crystallization of amorphous Al-Ni-Y alloys, giving a dispersion of nanometre-scale α-Al crystallites in an amorphous matrix, is studied using isothermal and non-isothermal DSC, XRD and TEM. Isothermal anneals followed by temperature scans reveal the influence of changing composition on the stability of the remaining matrix, A significant limitation on crystal growth can be the approach to metastable equilibrium with the amorphous matrix. In equilibrium, the volume fraction crystallized is lower for smaller crystallites because of the influence of the interfacial energy through the Gibbs-Thomson effect. The crystallite/matrix interfacial energy can be estimated from the dependence of equilibrium volume fraction on diameter. This dependence also gives rise to significant heat release during crystallite coarsening, and this is revealed in the shape of DSC peaks.