Microbiologically influenced corrosion of metallic materials: microstructure, coupled degradation mechanisms, and protection

Abstract

Microbiologically influenced corrosion (MIC) has conventionally been interpreted through microbial species, biofilm formation, extracellular electron transfer, and metabolite-driven chemistry. Recent significant advances in the fields of microbiology, electrochemistry, and interfacial characterization have enhanced understanding on the mechanisms of microorganism’s role in altering anodic dissolution, cathodic reactions, passive films, corrosion products, and local chemistry. However, the roles of alloy chemistry, microstructure, passive films, defects, and hydrogen transport govern the initiation, localization, and subsequent evolution of MIC remain insufficiently understood – an important aspect for engineering equipment, where localized corrosion, residual stress, cyclic loading, and hydrogen uptake act simultaneously and may drive the transition from surface attack to cracking. Keeping this in view, current understanding of the MIC mechanisms, with emphasis on the evolution of the biofilm–metal interphase, localized electrochemical gradients, microbial corrosion reactions, and electron transfer are summarized in this overview, with emphasis on mechanistic evidence. MIC across major metallic material classes are compared, which shows that alloy chemistry, phase constitution, inclusions, precipitates, grain boundaries, passive-film’s stability, weld heterogeneity, and corrosion-product structure determine where the MIC-induced damage initiates, whether it remains localized, and how hydrogen is transported and trapped. Microbiologically assisted cracking is summarized next, by linking biofilm-induced pitting with stress concentration, anodic dissolution, hydrogen entry, fatigue, stress corrosion cracking, and crack propagation. Recent advances in localized electrochemistry, cross-sectional microscopy, chemical imaging, isotopic tracing, and correlative characterization are then assessed, together with materials-oriented mitigation strategies based on antibacterial alloying, microstructure regulation, surface treatment, and functional coatings.