Search for Nucleation of Phase Embryos in Binary Alloys by Impurity Atoms

Abstract

A search was made to detect the possibility that individual impurity atoms in two-phase, binary alloys nucleate embryonic crystals. The alloy system studied was Ni-Al and the impurities were 111ln probe atoms. Local surroundings of the probes characteristic of the crystal phases were detected through quadrupole interactions with 111Cd daughter nuclei using the method of perturbed angular correlation of gamma rays. Analysis of site fractions of the probes led to two alternative interpretations that could not be distinguished on the basis of the present measurements: 1.) 111ln probes in the two-phase domain between Ni2Al3 and NiAl segregate to Ni2Al3 with a segregation energy of about 0.10 eV; or 2.) 111ln probes nucleate embryonic crystals of Ni2Al3, with the driving force for nucleation being an attraction between In atoms and Ni vacancies that is known to be strong in NiAl.