The Early-Stage Propagation of Localized Corrosion of a Sintered NdFeB Alloy in Aqueous Environments

To capture the initial corrosion of sintered NdFeB alloys, a quasi-in situ investigation of the localized corrosion behavior was conducted in low-conductive aqueous solutions. It was clearly observed that the corrosion pits were started from the active sites in matrix phase adjacent to the phase boundaries and the oxide rings were simultaneously deposited some distance from the pits. The spatial separation of the anode and cathode areas during the corrosion could be explained by the potential-pH diagram of Fe and the transportation of hydroxide and ferrous ions in the solution. Based on the variation of oxide rings with environmental factors, it was deduced that the ring-shaped deposition of corrosion products was cooperatively determined by the ferrous cations from pits and the hydroxide anion generation at the cathodic regions limited by the diffusion of oxygen from the bulk solution. This observation gives new insights into the galvanic corrosion of alloys in aqueous media.

Automated summary

A quasi-in situ investigation of the localized corrosion behavior in low-conductive aqueous solutions was carried out to capture the initial corrosion of sintered NdFeB alloys. It was observed that corrosion pits started from active sites in the matrix phase near phase boundaries, while oxide rings were deposited at a distance from the pits. The spatial separation of anode and cathode areas during corrosion was explained by the potential-pH diagram of Fe and the transportation of hydroxide and ferrous ions in the solution. The ring-shaped deposition of corrosion products was determined by ferrous cations from pits and hydroxide anions at cathodic regions, limited by oxygen diffusion from the bulk solution.