Surface Layer Effects on the Mechanical Behavior of Metals

摘要

The effect of the surface layer on the mechanical behavior of metals is discussed. There is a considerable body of experimental evidence to show that, even in uni-axially deformed specimens, the work hardening is not uniform throughout the cross-section. Rather, the work hardening characteristics of a surface layer that extends approximately 100 micrometers differs considerably from the work hardening characteristics of the interior. The surface layer is shown to have a very large influence on the stress-strain behavior as well as the creep, fatigue and stress-corrosion resistance. The effect of the surface layer on the activation energy and activation volume is discussed. The experimental evidence on polycrystalline metals indicates that in high and low temperature creep, fatigue, stress corrosion and tensile deformation, the dislocation sources near free surfaces operate at lower stresses and more profusely than those in the interior. As measured by X-ray diffraction line profile analysis, the dislocation density in the surface layer, rho sub s, and in the interior, rho sub i increases during fatigue cycling and stress-corrosion exposure. The influence of environment on the mechanical behavior appears to be associated with surface layer.