Theoretical investigation of sulfur solubility in pure copper and dilute copper-based alloys

Dilute Cu-based alloys containing S, P, and Ag impurities and also vacancie s are studied theoretically on the basis of total energy calculations. This is done within the supercell approach by using the locally self-consistent Green's function (LSGF) method. The impurity solution energies; volume mis fits, and interaction energies for these defects are calculated and used to study the microscopic mechanism behind the effect of these impurities on e mbrittlement of copper at intermediate temperatures. It is shown that the s olubility of S in Cu is low due to precipitation of the highly stable Cu2S phase. A large binding energy of a sulfur-vacancy defect pair in the first coordination shell (-0.46 eV) and a sulfur-sulfur defect pair in the second coordination shell (-0.12 eV) seem to favor this precipitation. The effect of phosphorus and silver impurities on the bulk S solubility has also been studied, and was found to depend on the competition of these impurities wi th sulfur for vacancies, as well as probably for other lattice defects. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.