TEM and RBS/channelling of nanosized bicrystalline (Pb,Cd) inclusions in Al made by sequential ion implantation

Sequential ion implantation of Pb and Cd in Al at 425 K and 475 K respectively has been used to produce dense distributions of nanosized (Pb,Cd) inclusions with equiatomic composition. Pb and Cd form a simple eutectic system, but both elements are insoluble in solid Al, and the inclusions are Cd-rich in comparison with the eutectic composition. Inclusions in the size range from 1 to 20 nm were observed in as-implanted samples. Their overall shape was nearly cuboctahedral. Most of the inclusions were bicrystalline with an fee Pb part forming a segment of a cuboctahedron and an hcp Cd slab attached to one of the {111}(Pb) facets. The orientation relationship had close-packed planes and directions parallel in the three structures, In situ melting/solidification experiments combining TEM and RBS/channelling showed that melting of the inclusion ensemble occurs within a narrow temperature interval of 10-15 K around the eutectic temperature of 521 K. Solidification takes place with undercoolings of about 50-65 K below the liquidus line in a two-stage process where Cd solidifies 15 to 20 K before Pb.