Mechanism of embrittlement of metals by surface-active elements

Abstract

The nature of mechanical degradation of metals caused by surface-active elements is studied based on the effects of iodine and gallium in austenitic steels and using ab initio calculations and experimental measurements of electronic structure, X-ray diffraction, mechanical spectroscopy, and mechanical tests. A significant increase in the density of electron states at the Fermi level for iodine in f.c.c. iron is shown that is in consistent with the measurements of the increased concentration of free electrons caused by iodine in austenitic steels. Consequently, the increase in mobility of dislocations by iodine and gallium in austenitic steels is revealed. The localization of the enhanced plastic deformation is discussed as a condition for brittleness. The obtained results are at variance with the widely spread opinion about the determining role of surface energy in a liquidmetal brittleness and, instead, are interpreted based on the correlation between atomic interactions and dislocation properties. Applicability of the available HELP and AIDE hypotheses is discussed.