Metal Failure in Electrolytes Under Mechanical Stresses

2 Metal Failure in Electrolytes Under Mechanical Stresses 

Below is a brief account of the mechanical aspect contribution into corrosive wear. Failure of materials is treated today as a discrete process of jerky local elementary acts repeated periodically in time [15]. Since metal friction has a pulse behavior and metals wear by the fatigue mechanism [16], so friction and wear in corrosion-active media should be treated as the interrelation of the process with adsorption and corrosive fatigue. Adsorption fatigue usually paves the way for corrosion processes in the materials and precedes stronger effects in the media where the rubbing bodies operate [17]. 

The mechanical properties of the majority of crystalline materials are conditioned by their dislocation behavior. Consequently, the effect of the medium on the mechanical properties of solid bodies can be induced by interactions with dislocations and imperfections of the surface structure. The conditions at the solid-medium interface are dependent on the free surface energy. It is generally accepted that the strength of solid bodies is a value proportional to their surface energy. 

The effect of the medium on metal deformation commonly begins on reduction of the surface energy during physical adsorption. Afterwards, various secondary phenomena, including chemical, electrical, etc. are superimposed on this process. A certain activation energy, dependent on the process specifics, is necessary for these phenomena to occur. In the case of metal strain and failure in corrosion-active media, mechanical and electrochemical activation are of particular importance [18]. 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

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