Thermodynamic framework for characterization of flow-induced corrosion

Corrosion-induced material degradation is a significant challenge across various industry sectors. The synergistic interaction of corrosion with other degradation mechanisms like wear, fluid motion, and erosion tends to increase its detrimental effects substantially. While the synergy between wear and corrosion in low-carbon steels has been studied, this work focuses on a less-explored interaction: the influence of electrolyte motion induced by non-contact sliding on corrosion degradation. Experimental findings demonstrate that corrosion-induced material degradation is influenced by electrolyte motion induced by the reciprocating movement of sliding pairs in the absence of contact, an effect not previously considered in existing models. Furthermore, an appropriate approach for conducting open circuit potential (OCP) measurements prior to applying the desired voltage in corrosion studies is proposed. Surface analyses using 3D profiling and microscopic analysis confirm variations in material removal and topography between static and dynamic conditions of the electrolyte. To model this synergistic effect, we employ the Degradation Entropy Generation (DEG) theorem developed in accordance with the laws of irreversible thermodynamics. The DEG framework introduces the degradation coefficient B, establishing a relationship between material loss due to corrosion and entropy generation. Experiments with varying overpotential and pin speeds (inducing different electrolyte motions) revealed a consistent linear relationship between material degradation and entropy generation, irrespective of experimental conditions. The findings are supported by the magnified surface images obtained through Scanning Electron Microscopy (SEM) and the elemental composition data acquired from Energy Dispersive X-ray Spectroscopy (EDS) analysis of samples exposed to various corrosion conditions. This outcome highlights that the degradation coefficient B is independent of corrosive conditions and electrolyte motion, which is valuable for modeling corrosion behavior under varying operating conditions and essential for future tribo-wear modeling.