Pitting potentials E~, and protection potentials, E~p, have been determined for a-brass (33% Zn) using a cyclic polarlzahon method. Increasing the F concentratmn shlJ~s the crlhcal potential to more active values. The pitting potentials, Ep, and protection potentials, Ep depend on the logarithmic concentration of F-ions according to the equations: Ep = a + b log [F ] and Epp = a + b log [F ~. Slow strain rate tests (SSRT), at a strain rate of 5 • 10 5 s-~, were performed under open-circuit and potentiostatic conditions to study the stress corrosion cracking (SCC) characteristics of the a-brass in NaF solutions of various concentrations (pH 6.8) at 25~ The minimum concentration of NaF that caused intergranular stress corrosion cracking (IGSCC) was 1 • 10-4M. This concentration, was also the critical level for repassivation, observed in cyclic polarization tests. These results demonstrate a good correlation between the electrical and the mechanical breakdown of the passive film. In the presence of 10 ~M NaF the potential range for IGSCC was -150 to -50 mV (SCE). These critical potentials were restricted to the stable passive potential range and also fell within the potential-pH region where Cu~O was stable. The formation of a Cu20 film on the brass after polarization in the passive region was confirmed by x-ray diffraction (XRD). At more noble potentials and at cathodic potentials below the Cu20 domain, the failure mode was ductile fracture. These observations of IGSCC of the brass in fluoride solutions support a film rupture-dissolution mechanism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.