DECOMPOSITION KINETICS OF BULK AMORPHOUS ZR41TI14CU12.5NI10BE22.5 ALLOYS STUDIED BY COMPUTER-SIMULATION AND SMALL-ANGLE NEUTRON-SCATTERING

The decomposition behaviour during annealing in the undercooled liquid regime of Zr41Ti14Cu12.5Ni10Be22.5 is studied by means of small-angle neutron scattering (SANS). In this temperature range, a microstructur e consisting of precipitates of an amorphous phase is formed. The scat tering curves show a characteristic maximum which becomes more and mor e intense with increasing annealing time until a saturation state is r eached. All scattering curves at different annealing times obey a univ ersal scaling law by scaling the intensity and the q axis by the inten sity and the position of the maximum, respectively. In order to interp ret the scattering curves, the scattering behaviour of a system of int eracting particles and its time evolution are simulated. The centres o f the precipitates are modelled (either analytically or numerically) b y 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 crea ted according to a given nucleation rate, either instantaneously (all nuclei start growing at the same time) or continuously (in each time i nterval, 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 interpr etation: The amorphous precipitates are distributed according to a har d-core structure and the nucleation is continuous. The growth of the p recipitates is diffusion controlled (a proportional to t(1/2)).