Efeito da concentração de NaCl na tribocorrosão de aços inoxidáveis

Abstract

The present work aimed to study the effect of NaCl concentration in the stainless steel tribocorrosion. Understanding the impact of chloride content variation is important as it directly affects corrosion kinetics. The salinity in marine environments, for example, varies by factors such as distance from the coast, depth, local climatic and atmospheric conditions, varying the chloride content in the environment. Applications in the food processing and mining industry can also feature systems with varying concentrations of Cl-. The methodology was based on sliding tribological tests, pure corrosive tests and tribocorrosion tests, aiming to evaluate purely mechanical degrading mechanism and corrosion resistance in absence of mechanical wear and, finally, analyzing the combined action of mechanical, electrochemical mechanisms. Tests were performed in four different media, distilled water (tribological sliding tests) and three different NaCl solutions, 0,05 %, 1,78 % and 3,56 % (corrosion and tribocorrosion tests). The tested specimens were made of AISI 304 (austenitic) and AISI 410 (ferritic) stainless steels and, for comparative purposes, carbon steel ASTM A36. Zirconia (zirconium oxide) balls were used, as counter body, in the sliding and tribocorrosion tests. From the tests, were collected the potentiodynamics curves, the evolution of friction coefficient and the mass variation for calculating the wear and degradation rates. Tribocorrosive tests showed a decrease in the friction coefficient compared to the sliding ones. The increase in NaCl concentration imposed greater corrosion severity and decreased the friction coefficient, showing the lubricating effect of corrosion products on contact.The worn surfaces SEM and EDS analysis indicate a shift of degradation mechanisms, with the prevalence of chemical effects with increasing NaCl content. Among the stainless steel, 304 exhibits the highest friction values in sliding tests and the lowest friction values in tribocorrosion tests. The carbon steel had the lowest friction coefficient values among the tested materials, also showing the highest degradation rates in the tribocorrosive tests. In contrast, among the stainless steels, 410 had the highest degradation rates at greater NaCl concentrations.