POSITRON TRAPPING AT PRECIPITATES IN AU-26.5 AT.PERCENT PT

The precipitation kinetics of the Au-26.5 at.% Pt alloy, quenched with in the miscibility gap and annealed isothermally at 900 K, was studied by positron annihilation spectroscopy (PAS) using the lifetime techni que as well as the Doppler broadening technique. Information on the si ze of the platinum-rich precipitates was obtained from small-angle neu tron scattering (SANS) measurements. The results of the PAS measuremen ts were interpreted by assuming that a fraction of the positrons, depe nding on the morphology of the material, is trapped at misfit dislocat ions on the boundaries of platinum-rich precipitates. The positron tra pping rate per unit specific area of the interphase boundary was obtai ned by combining PAS data with SANS results. The discussion points out the importance of this parameter and of the positron lifetime data fo r a characterization of the local structure of the interphase boundary . By assuming that the growth kinetics of the platinum-rich precipitat es is governed by a t(1/3) law, we obtain from our data quantitative i nformation on the shape of the size distribution of the precipitates.