Effect of the surface status on corrosion fatigue of the strained structural materials

Abstract

Fatigue failure of metal structures during operation is a frequent cause of machinery and equipment failure, and sometimes of human losses. This is especially true for operating conditions in the presence of corrosive environment. Reliable and safe operation of metal products and engineering devices during operation is largely determined by the structure and properties of the used materials and is ensured by optimizing the process operating conditions. The analysis of domestic and foreign literature data has shown that systematic theoretical and experimental studies of the impact of corrosive environment on the resistance to alternating loads on strained metals and alloys are practically absent. In this regard, the issue of identifying the patterns of corrosion and fatigue failure seems to be urgent in order to increase the corrosion fatigue life of plastically strained metals and alloys. This paper analyzes the impact of the status of surface layers of structural metals in a thermally treated and plastically strained state. The factors influencing the metals oxidation susceptibility have been established. During cyclic loading all processes related to vacancies’ concentration and fatigue cracks nucleation are ahead of schedule in the surface layers of metal, and all structural damage is concentrated at the surface, especially in case of corrosion fatigue. Plastic deformation increases both the thermodynamic possibility of oxide formation on the metal surface and the speed of this process. An increase in the active sites density on the surface of the strained metal contributes to the emerging of a large number of oxide nuclei, the growth of which leads to a faster formation of a continuous passivating film than on the surface of an unstrained metal.