Work

Effect of Cr:Al Ratio on Corrosion Mechanism of Ni-Cr-Mo-Al Alloys in 3.5 wt.% NaCl Solution: Microstructure and Electrochemical and Passive Characteristics

Year: 2025

Type: article

Abstract: In this study, the microstructure and electrochemical and passive characteristics of NiCr25.2−xMoAlx (x = 0, 1.25, 2.5, and 5 mol.%) alloys were investigated. The results show that Ni-Cr-Mo-Al alloys with varying Cr:Al ratios both had a single FCC structure without any second structure precipitates, and decreases in dislocation density and grain size were observed as the Al content in NiCrMoAl alloys increased. It was found from the electrochemical results that the NiCr23.95MoAl1.25 alloys had the maximum radius for a semicircle and the lowest Icorr, indicating an enhanced anti-corrosion performance (Rct: 8.08 ± 0.368 × 105 Ω cm2, Icorr: 1.05 ± 0.003 × 10−7 A/cm2). In this study, it was found that the anti-corrosion performance of the alloys had an approximate connection to the composition and density of passive films. Denser and more stable microstructures in NiCr23.95MoAl1.25 alloys were further proven by potentiostatic polarization tests and Mott–Schottky experiments, showing a lower stable current density and acceptor density (NA: 9.79 ± 0.4 × 10−20 cm−3). In addition, the results of XPS show that the Al1.25 specimen had the highest Cr2O3 in the passive film’s content among the NiCrMoAl alloys. Cr2O3 was the main component, suggesting an enhanced protective influence of passive film. The present study can offer guidance for the application of nickel-based alloys with high anti-corrosion resistance in marine environments.

Source: Materials

DOI: 10.3390/ma18102177