The effect of solid surface films on the stress-strain properties of metals

The data available from the recent publications, as well as those obtained by the authors themselves in studying the effect of surface films on the mechanism of plastic deformation and on the mechanical properties of mono- and polycrystalline materials, have been systematized. Hard surface films are capable of changing the flow stress, strength, plasticity in elongation, characteristics of creep, fatique, and other mechanical properties of metals. When there are the films of chromium on single crystals of siliceous iron, there takes place a change in the mechanisms of deformation: deformation by slippage gives way to twinning in siliceous iron. High-strength films, for example, oxide films upon aluminium, cadmium and other metals hamper the development of plastic deformation in metals, which is conductive to brittle failure. Under the influence of titanium films, molybdenum and tungsten are characterized by a decreased flow stress, a lower temperature of brittle transition and an increased elongation. It has been suggested that the basic mechanism by which the surface films exert their influence on the metals they cover is associated with their action on the superficial sources of dislocations. The surface films are capable of blocking and deblocking th. above-mentioned dislocational sources, thereby hindering or facilitating the development of plastic deformation in metals