Decomposition Kinetics of Bulk Amorphous Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 Alloys Studied by Computer Simulation and Small-Angle Neutron Scattering

The decomposition behaviour during annealing in the undercooled liquid regime of Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 is studied by means of small-angle neutron scattering (SANS). In this temperature range, a microstructure consisting of precipitates of an amorphous phase is formed. The scattering curves show a characteristic maximum which becomes more and more intense with increasing annealing time until a saturation state is reached. All scattering curves at different annealing times obey a universal scaling law by scaling the intensity and the q axis by the intensity and the position of the maximum, respectively. In order to interpret the scattering curves, the scattering behaviour of a system of interacting particles and its time evolution are simulated. The centres of the precipitates are modelled (either analytically or numerically) by a hard-core point field, i.e. they have a minimum distance from each other (`excluded volume'). At each of these points, a nucleus is created according to a given nucleation rate, either instantaneously (all nuclei start growing at the same time) or continuously (in each time interval, a constant number of nuclei starts growing). Variation of the parameters of the hard-core point field, the nucleation mechanism and the growth law for the precipitates and comparison of the calculated and measured small-angle scattering curves allow the following interpretation: The amorphous precipitates are distributed according to a hard-core structure and the nucleation is continuous. The growth of the precipitates is diffusion controlled (a ∝ t ^1/2).