On the corrosion characteristics of some commercial magnetic metallic glasses in NaCl solution

Abstract

The corrosion characteristics of six commercial magnetic metallic glasses, namely Fe78B13Si9 (Metglas 2605-S-2), Fe67Co18B14Si (Metglas 2605 Co), Fe40Ni40B20 (Vitrovac 0040), Fe39Ni39Mo2(SiB)20 (Vitrovac 4040), Fe40Ni38Mo4B18 (Metglas 2826 MB) and Fe40Ni40P14B6 (Metglas 2826) in which iron and boron are common base elements have been studied by immersion tests and potentiostatic techniques in various concentrations of NaCl solutions at room temperature. In exposure for up to six days, weight loss observations indicated that the corrosion rates in 3.5% NaCl were in the following increasing order: 2826 < 4040 < 0040 < 2826 MB < 2605 Co < 2605-S-2. During exposure for up to four hours under open-circuit conditions, 2826 alloy showed the noblest behaviour while 2605-S-2 was the least noble. All the alloys, except 2826, showed rapid dissolution without any passivation during anodic polarization. Phosphorus addition to Fe-Ni-B glass enhanced the active dissolution and resulted in the formation of a black prepassive film in the active region (0.2V) which becomes protective in the passive region (0.3 to 1.25V). The values ofIcrit. andIpass. (the critical and passive current densities) decreased with a decrease of concentration from 3.5 to 0.01% NaCl, while in 0.001% NaClIpass. slightly increased and the passivation potential range decreased. The corrosion resistance of Fe-B metallic glasses increased with metal addition in the order Co < Mo < Ni and with metalloid addition in the order Si < P.