Abstract
The localized corrosion properties of a series of iron-based metallic glasses containing either the elements Fe-Cr-Mn-Mo-W-B-C-Si or Fe-Cr-Mo-W-B-C-Y have been studied in near-neutral pH, sodium chloride (NaCl) solution, and concentrated hydrochloric acid (HCl) solution over a range of temperatures. Findings were compared to Ni-based Alloy 625 (UNS N06625), Alloy 22 (UNS N06022), and other Fe-based alloys exposed to the same environment. Excellent resistance to pitting corrosion was observed in 0.6 M NaCl at 25, 50, and 85°C in the fully amorphous state during both upward potentiodynamic scans and when activated pits were formed. E-I data was also acquired by the artificial pit method. Additionally, electrochemical and gravimetric testing in 0.1-, 1-, 5-, and 10-M HCl solutions verified extremely low corrosion rates in the case of high Cr-, Mo-, and W-containing glasses. Pitting and crevice stabilization potentials were also predicted from electrochemical data developed using a 10-M HCl solution to simulate the chemistry inside a pit. The predicted critical pitting, ET, and crevice potentials, Ecrevice, associated with acid local corrosion stabilization were determined from the sum of the corrosion potential, a charge-transfer overpotential, and the ohmic voltage required to achieve two different critical pit-stabilizing current densities. Pits and crevices of various assumed geometries were examined. Exceptional localized corrosion resistance in acidified and neutral Cl− solutions can be rationalized to be influenced by at least three factors. These include the large concentrations of Cr, Mo, and W in solid solution in the glass phase, minimization of surface defects, as well as several possible unresolved roles of minor and trace alloying elements such as Mn, B, C, Y, and Si on corrosion behavior.
