SURFACE PHENOMENA IN SOLIDS DURING THE COURSE OF THEIR DEFORMATION AND FAILURE

Abstract

The fact that deformation and failure are facilitated by the reversible physico-chemical influence of the medium has been established by now for all types of solids: for metals (and also certain covalent crystals) in contact with liquid metals, for ionic crystals and inorganic glasses in the presence of molten salts, water, alcohol, or other polar media, and for molecular crystals of organic compounds in contact with nonpolar and low-polarity organic liquids. In general these phenomena facilitate the breaking and realignment of the interatomic bonds in the presence of certain foreign atoms or molecules (which have sufficient mobility to ensure their penetration into the bond-breaking zone) and can be described as a lowering of the free surface energy of the given solid under the influence of the surrounding medium. The main condition under which the medium exerts a strong influence on the mechanical properties of the body (in cases of reversible adsorption interaction not connected with dissolution, corrosion, or other chemical processes) is that the solid and the medium be of related nature, to make the surface energy low on the boundary between the solid and liquid phases. At the same time, the form and degree of manifestation of these effects depend in a complicated manner on the real structure of the body (defects) and on the deformation conditions (stresses, temperature, strain rate, time of contact, etc.) An optimal combination of these factors makes it possible to use the influence of the medium to facilitate dispersion and treatment, particularly of solid materials that are difficult to work. To the contrary, by eliminating individual factors that lower the strength by adsorption it becomes possible to protect against the influence of the medium.