Phase-resolved in-situ electrochemical and chemical mapping of 2205 duplex stainless steel corrosion via combined MECT-SECM approach

Understanding phase-specific corrosion behavior in multiphase alloys is critical for elucidating localized corrosion mechanisms. In this study, an integrated microelectrochemical cell technique (MECT) and scanning electrochemical microscopy (SECM) approach was developed to investigate in-situ electrochemical activity and local chemical environments on 2205 duplex stainless steel. Using a custom-fabricated dual-channel pipet, spatially resolved potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements were performed at the α (ferrite) and γ (austenite) phases. Austenite exhibited higher corrosion current density i corr (60.4 μA·cm -2 ), lower charge transfer resistance R ct (39.2 kΩ·cm²), and reduced low-frequency impedance ( |Z| 0.1 Hz = 19.4 kΩ·cm²), indicating its preferential dissolution as the local anode in micro-galvanic coupling. Complementary in-situ pH mapping using a solid-state W/WO x micro-sensor revealed localized acidification and alkalization zones after 22, 32, and 56 h of immersion in acidic NaCl solution (pH = 1.5), coinciding with the onset and propagation of pitting. This dual-technique strategy provides unprecedented phase-resolved insight into corrosion dynamics, linking structural, electrochemical, and chemical heterogeneities across microdomains. The findings underscore the effectiveness of MECT-SECM integration for mechanistic studies of localized corrosion in duplex stainless steels and other complex alloys.