Solute-defect interactions in a metastable Pb–Ni alloy formed by high-fluence ion implantation

Abstract

Implantation of 240 keV Pb+ ions into a Ni (110) single crystal to a fluence of 1016 cm−2 at room temperature and 470 K, respectively, resulted in the formation of a metastable supersaturated Pb–Ni solid solution with a maximum lead concentration of 2.4 at. %. Rutherford backscattering/channeling analysis and transmission electron microscopy have shown that in the as-implanted state most of the Pb atoms were distributed on substitutional lattice sites in the host matrix while a small fraction of Pb was confined within nanoscale precipitates. Most of the precipitates, with sizes ranging from 2 to 15 nm, were single crystalline although bi-, tri-, and tetracrystals were occasionally observed. Upon heating, decomposition of the metastable alloy was observed, with strong outdiffusion of a large fraction of Pb to the surface. By means of angular scan channeling analysis, the lattice location of the implanted Pb atoms was followed directly during in situ isochronal annealing at different temperatures up to 860 K. Thermally activated formation of Pb atom–vacancy complexes was found to cause originally substitutional Pb atoms to change to different types of lattice site occupation. The regular and distorted substitutional, octahedral interstitial, and random locations of the Pb atoms appeared to be strongly correlated with the temperature of the annealing.