On the corrosion and passivity of Inconel alloy 625 in HNO3 solution
Khashayar Morshed-Behbahani, Ali Nasiri
Abstract
• Examined alloy 625 corrosion and passivity in nitric acid via electrochemical methods. • Solution concentration variations caused corrosion response changes in DC experiments. • Characterized passive films in a duplex structure: Cr 2 O 3 and F 2 O 3 /NiFe 2 O 4 . • PDM correlated solution concentration to passive film point defect diffusivity. Exploring the passivity and electrochemical behavior of Inconel alloy 625 in nitric acid solution could open up possibilities for potential applications, either in bulk form or as claddings. Hence, this research investigates corrosion behavior and passivity of Inconel alloy 625 in nitric acid solutions of varying concentrations (0.01–1.00 mol/L) using a range of analytical techniques, including potentiodynamic polarization testing, chronoamperometry measurement, Mott-Schottky (MS) analysis, X-ray diffraction (XRD) approaches, and point defect modeling (PDM). Results demonstrate that corrosion current density does not necessarily decrease with increasing electrolyte concentration (Please check it out). Additionally, the alloy exhibits higher passive film transpassive potentials in more concentrated solutions. Potentiostatic polarization tests reveal an increase in steady-state current densities attributed to the passive films formed in more concentrated solutions. Lower electrolyte concentrations lead to the formation of more intact bilayered passive films. In this context, the formation of passive films is elucidated by examining the generation and annihilation of point defects. The semiconducting behavior of passive layers is further examined through XRD patterns and electrochemical properties. According to PDM, the diffusivity of point defects within the passive films and their respective donor densities can be closely correlated.