Influence of the Extracts of Plant Raw Materials on the Corrosion-Fatigue Fracture of Steels in Fresh Water
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INFLUENCE OF THE EXTRACTS OF PLANT RAW MATERIALS ON THE CORROSION-FATIGUE FRACTURE OF STEELS IN FRESH WATER Z. V. Slobodyan,1 L. A. Mahlatyuk,1 Ya. M. Khaburs’kyi,1, 2 and R. B. Kupovych1
UDC 620.197.3
The necessity of taking into account the contribution of corrosion-fatigue fracture is substantiated. Together with corrosion and salt deposition, this type of fracture complicates the reliable operation of heat-exchange systems. An important role of the deformation of specimens in the variations of the wettability of steel surface by water and inhibited solutions is demonstrated. It is shown that the increase in the level of strains in the specimen intensifies the hydrophilization of the steel surface. The wetting angles of the steel surface by aqueous extracts of oak are lower than the angles of wetting by water in the entire investigated strain range (1.86–13.3%), which corresponds to the predominant adsorption of the components of inhibitors as compared with water. It is shown that if water periodically wets the specimen surface, then it significantly decreases the resistance of steels to the corrosion-fatigue fracture as compared with air. The oak-bark extract (2 g/liter) increases the resistance of steel to this type of fracture for low levels of loading by a factor of 2.6 as compared with water. Moreover, the mechanism of fracture in the stage of crack origination changes from the intergranular fracture in water to the transgranular fracture in the inhibited medium. This enables to recommend the inhibitor based on the oak-bark extract not only for the retardation of corrosion processes but also for the inhibition of corrosion-fatigue fracture. Keywords: green inhibitors, corrosion-fatigue fracture, wetting angle, strains, fractography.
The operation of the systems of recycling water supply is strongly complicated by the corrosion processes and the deposition of salts, which results in the deterioration of heat exchange, excessive consumption of the electric energy, etc. Moreover, the variations of the hydrodynamic mode of water flow induce the formation of corrosion-fatigue defects [1]. The fatigue fracture of metals in corrosion media is a specific synergetic phenomenon with mutual intensification of the corrosion and fatigue processes. The danger of corrosion-fatigue fracture is connected with its difficult detection in the early stages when the process runs without noticeable changes in the state of the surface [2]. In practice, the protection of water recycling systems against the first two processes is successfully realized by the use of inhibitors of complex action. However, the applicability of inhibitors under cyclic loads requires additional analysis. Most inhibitors are surfactants. It is known that the adsorption of surfactants and, in particular, of alcohols or organic acids leads to a significant decrease in the resistance of the metal to deformation and fracture [3]. On the other hand, some inhibitors exhibit high protective properties under the conditions of highand low-cycle fatigue [4–6]. The
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