Crevice Corrosion of Glassy Fe-Ni-Cr-P-B Alloys

Abstract

Crevice corrosion of glassy Fe-Ni-Cr-P-B alloys in NaCl electrolyte was investigated as a means of differentiating between initiation-related and propagation-related corrosion behavior. Specimens containing deformation-induced surface microcracks experienced a transient type of crevice attack at potentials only slightly anodic to the free corrosion potential. However, the crevices widened into pit shaped voids and quickly passivated, apparently as a result of ingress of bulk electrolyte. Separate experiments with alloys cold worked in compression showed complete absence of attack at shear bands, indicating the need for microcracks for localized attack. Experiments with an electrochemical crevice cell, instrumented to record changes in anode potential and anolyte pH, required polarization above about 1 V (SCE) to cause crevice corrosion. The potentials of crevice specimens did not decrease substantially during corrosion, indicating the possible presence of a partially protective film. It was concluded that the alloys exhibit a high degree of resistance to crevice corrosion that parallels their excellent pitting resistance.