Electron microscope studies of the mechanism of nucleation and growth of Cu Au ii from the disordered state

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Abstract
Thin single crystal films of Cu Au prepared by evaporation have been studied on a hot stage inside the electron microscope. The alloy is disordered by annealing at 450 °C, and the nucleation and growth of ordered regions is studied as the temperature is lowered to some value in the range 380-400 °C. By use of dark field microscopy on superlattice reflections, the distribution of ordered nuclei within a disordered matrix is studied in detail, as well as the orientation distribution within the ordered nuclei. This latter distribution is explained in terms of (101) twinning of the Cu Au. Evidence is obtained that dislocations modify the growth of the ordered phase in their vicinity, and that in some circumstances preferential nucleation of order occurs on the dislocations. These observations are being compared with studies of the nucleation of order produced in bulk alloy which is thinned after the heat treatment