Clustering and precipitation of indium atoms in quenched Al-In crystals

Abstract

Crystals of Al containing 8–250 ppm In were quenched from 550–870 K into an H 2O-HCl bath at 200 K and then were annealed up to 500 K in order to study the precipitation of In atoms. The samples were analysed by backscattering-channeling measurements and by perturbed γγ angular correlation (PAC) measurements, using radioactive 111In atoms. The fraction of In atoms which were in the form of pure In precipitates was determined from the 22 MHz PAC frequency (measured at 77 K), and from the nonsubstitutional fraction of In atoms using the channeling data. During annealing of the quenched alloys, a 47 MHz PAC frequency appeared near 300 K, and a frequency around 70 MHz appeared near 400 K. These frequencies are attributed to small clusters of In atoms and vacancies, representing precursor states of the larger precipitates. After annealing at 500 K, a considerable fraction of In atoms showed a wide distribution of PAC frequencies close to zero. indicating a strained coherent In precipitate with cubic symmetry; channeling data supported the coherency of this precipitate, and in addition showed considerable mass transport of In atoms to the surface. This combined technique of ion beam and PAC analysis has yielded new information about the solubility of In in Al.