NUCLEATION IN A NI-13 AT-PERCENT AL-ALLOY - POLARIZED NEUTRON-SCATTERING STUDIES AND CLUSTERDYNAMICS MODELING

The early stages of the decomposition reaction in an isotopically opti mized Ni-58-13 at% Al alloy at T = 450 degrees C have been studied by means of small- and wide-angle polarized neutron scattering (SWAPNS). Number densities of extremely small Ni3Al clusters with diameters less than 1 nm and the development of the cluster size distribution during the earliest stages of decomposition have been determined. The observ ed decomposition kinetics have been interpreted by means of cluster-dy namics model calculations. No nucleation energy larger than kT was fou nd to impede the decomposition reaction.