Characterization of the Native Passive Film on Ferrite and Austenite Phases of Sensitized 2205 Duplex Stainless Steel

Abstract

The influence of isothermal sensitization of 2205 duplex stainless steel (DSS) in 850°C was quantified using double-loop electrochemical potentiodynamic reactivation test. We assessed the microstructure, Volta potential distribution, and semiconductive properties of the native passive film on individual austenite and ferrite phases of solution annealed and sensitized DSS, using optical and scanning electron microscopy, scanning Kelvin probe force microscopy, and scanning tunneling spectroscopy. Beside conventionally used line profile scans, we used a multi-modal Gaussian distribution method for analyzing the Volta potential distribution over the entire scanned area. The Volta potential distribution evaluations indicated that the driving force for preferential corrosion at the ferrite/austenite interface in DSS increases after sensitization. Scanning tunneling spectroscopy revealed that the formation of intermetallic phases and depleted zones in DSS after sensitization, decrease the surface energy bandgap in both austenite and ferrite phases, whereas the density of electronic states in these phases increases, compared to those of solution annealed DSS. The multi-analytical approach that is used in this research provides complementary evidence for the detrimental effects of sensitization on corrosion resistance of DSS.

Sigma and Chi Phases Analysis in UNS S32750 Superduplex Stainless Steel by Optimized Linear Sweep Voltammetry in Alkaline Medium

“…These characteristics are mainly attributed to the fine biphasic microstructure, composed of approximately equal parts of austenite (γ) and ferrite (δ). [1][2][3][4][5][6] However, SDSS can undergo detrimental microstructural changes, mainly due to high diffusivity of certain alloy elements in the ferrite phase, when exposed to services at high temperatures and/or as consequence of inadequate fabrication processes, such as hot forming, welding. Thus, secondary phases, such as carbides, nitrides and mainly intermetallic phases like sigma (σ) and chi (χ) phases, can precipitate from the ferritic phase.…”

Challenges and Strategies for Optimizing Corrosion and Biodegradation Stability of Biomedical Micro‐ and Nanoswimmers: A Review

“…Moreover, internal galvanic coupling can also occur between various phases of composite MNSs. [22,85,90] Note that the dynamic conditions of the human body and the presence of various biological substances can cause the passive electrochemical potential of metallic MNSs to shift toward a more positive value, which subsequently increases localized corrosion on the active site. [91] Consequently, metallic MNSs may gradually fail to achieve the desired swimming speed, efficiency, and controllability due to degradation at active component sites.…”