Impurity-induced vacancy clustering in cold-rolled nickel alloys as studied by positron annihilation techniques

Clustering of vacancies in cold-rolled binary nickel alloys containing 1 at.% of Al, Ti, Ge, Zn, Sb, Pb and In has been investigated by positron annihilation technique (lifetime, Doppler broadening and angular correlation peak counting-rate measurements). The most intensive clustering of vacancies was observed for alloys containing oversized, polyvalent solutes: Sb, As, Pb and In. The effect of Zn and Ge admixtures is much weaker. Ti, Al and W admixtures do not induce the clustering of vacancies. The tendency for clustering of the vacancies correlates well with the values of the solute-vacancy binding energy estimated on the basis of the vacancy model of melting of metallic materials.