Environmentally assisted fracture behavior of Fe-based amorphous coatings in chloride-containing solutions

Environmentally assisted fracture behaivor of Fe-based amorphous metallic coating (AMC) sprayed on 316L stainless steel was investigated in chloride-containing solutions using a slow strain rate test method in situ electrochemical measurements and subsequent fractography analysis. A systematic detrimental effect of applied loading and aggressive ions on passive current density and localized corrosion was found. The high applied loading deteriorated the stability of passivation of AMC, which increased the passivation density and the pitting tendency. The fracture surface of AMC exhibited brittle fracture morphology with no significant crack branching. A mechanism was proposed in which the localized corrosion taking place preferentially at coating defects, and for producing the necessary crack-tip geometry. The tensile stresses accelerated the localized corrosion susceptibility near the defects by forming microcracks and promoting fast diffusion path for chloride ions. The poor environmental cracking resistance of AMC was attributed to the low protective effect of the passive film for the stress assisted localized corrosion at the crack tip and to the metastable nature of the amorphous structure. (c) 2017 Elsevier B.V. All rights reserved.