EVOLUTION OF LEAD PRECIPITATES IN ION-IMPLANTED ALUMINUM

Aluminium-lead alloys are characterized by extremely low miscibility i n the solid phase across the entire equilibrium phase diagram. Ion imp lantation of lead into aluminium at room temperature therefore results in spontaneous phase separation and formation of nm-size lead precipi tates growing in topotactical alignment (epitaxy in three dimensions) with the aluminium matrix with a cube/cube orientation relationship. T ransmission electron microscopy (TEM), Rutherford backscattering spect rometry (RBS) and channeling techniques were used to analyze the forma tion and evolution of lead precipitates during implantation and subseq uent annealing. Implantations at room temperature induce a microstruct ure characterized by very small (2-5 nm) precipitates embedded in a he avily damaged matrix. Only approximately 50% of the implanted lead ato ms are retained in precipitates while the rest are in supersaturated s olution or in small (< 1 nm) Pb clusters. Annealing of the samples res ults in an increase in the size of the inclusions. With RBS/channeling analysis we observe two different stages in this growth: (1) incorpor ation of the initially dispersed fraction of lead atoms and, (2) coale scence of precipitates. The larger crystallites were found to improve channeling in the lead. A similar change in the microstructure of the inclusions was found after implantation at elevated temperatures.