Localized Corrosion of Fe‐B‐Si Glassy Alloys

Abstract

The glassy alloys Fe75B25−xSix with x<12% at. exhibit a breakdown of passivity in borate buffer solution with no aggressive ions added. This instability of the passivating film, leading to a localized corrosion, ceases at x⩾12% at. XPS analysis suggests that at x=12% the passivating film consists mainly of SiO2 , the minor components being Fe2O3 and B2O3 . At x=9% the main constituents of the film are silicates, which exhibit a lower protective ability and cannot efficiently counteract the detrimental effect of boron compounds. Chlorides are harmful for passivity of the Fe‐B‐Si alloys; severe pitting occurs even at a chloride concentration as low as 10−4 M.

Effect of Si on the Corrosion behaviour of Fe‐B and Fe‐Ni‐B glassy alloys

“…It has been found that the corresponding locations of the data points for the passivating film on the 12% Si alloy confirm the assumption already made according to which the main constituent of the film is a silicon oxide [13]. The location of Werkstoffe und Korrosion 36, 441-446 (1985) the data points for the 9% Si alloy suggests that silicates rather than oxides are the main components of the passivating film in this case.…”

“…The existing data suggest that B is detrimental to the corrosion resistance of Fe-B alloys in acid solutions [14,15,241 and to the stability of the passive state in borate buffer solution [13,151. The present results show that Si compounds in the passivating film on Fe-B-Si alloys can counteract the detrimental effect of B compounds.…”

“…Microscopic examinations have revealed that the sharp increase of current density for the alloys with <12% Si is caused by a breakdown of passivity followed by a localized corrosion similar to pitting [13][14][15]. At the active spots the pits grow quickly in depth and can perforate the ribbons even if no aggressive ions are present in the solution.…”

“…8b). Taking into account the corresponding binding energies of the photoelectrons of Feox2p, SbX2p and Box 1s [13] we assume that the constituents of the film are: SiO, Fez03 and B2O3. Considering the concentrations of individual constituents in the middle of the composition profile the following molar film composition results: -80% SOz, -10% Fez03 and -10% BZO3.…”

Electrochemical behaviour of Ni-Co amorphous alloys in alkaline solutions

“…These values indicate the presence of silicon oxide and/or silicates whose formation in slightly alka line electrolyte is probable. Furthermore, it was reported that silicon oxides are the main constituent of the film formed on amorphous alloys with a silicon content as high as 12% [24].…”