EFFECT OF VACUUM ON THE FATIGUE BEHAVIOR OF METALS AND ALLOYS

The present work is a review of investigations in the last decade of the effect of vacuum on the fatigue behaviour of metals and alloys. Interactions between solids and the environment are treated in terms of the physics of metals, and fatigue is considered as a multistage process of microplastic deformation that progresses to subsequent failure. Since surface and subsurface layers play a decisive role in plastic deformation and failure as a result of their specific positions, a large number of investigations have been concerned with the effect of the environment on processes taking place in the surface layer at the stages of hardening/softening and crack initiation. We therefore present results on the effect of vacuum on fatigue in alloys surface hardened by plastic deformation. In addition, the effect of vacuum on plastic strain at the tip of a crack is analysed in relation to changes in the microstructure and macrostructure of fatigue fractures. The causes of the dependence on the structural state of an alloy of the effect of vacuum on fatigue life are discussed. It is concluded that the mechanism of the vacuum effect on fatigue behaviour depends on the fatigue mechanism itself which is characteristic for a metal or alloy in given loading conditions. On this basis modern concepts of the physics of plasticity and dislocation mechanisms of plastic strain are analysed in relation to various mechanisms of fatigue. © 1979.