Stress corrosion cracking behavior of alpha-brass as a function of the oxide transport properties in NaNO2 solutions

In this paper, we relate the transport properties of the anodic oxide films formed on alpha -brass in NaNO2 solutions to the mechanical response of th e alloy during slow strain rate tensile tests. A range of electrolyte conce ntrations were investigated, from 5 x 10(-4) M (pH 7.1) to 8.4 M (pH 8.8). Surface analysis [X-ray photoelectron spectroscopy, Auger electron spectros copy (AES), and AES depth profiling] techniques were used to investigate th e films composition. We begin by defining an electrochemical and mechanical criterion of crack initiation. Then three concentration regimes are reveal ed, for which a net correlation can be established between the oxide film p ermeability to metal cations and the susceptibility to stress corrosion cra cking (SCC): (i) in the dilute regime, the passive film on alpha -brass is highly permeable while crack initiation requires high mechanical loading; ( ii) in the intermediate regime, both the protective character of the oxide film and the susceptibility to SCC are maximum; and (ii!) in the concentrat ed regime, on the contrary, both the film permeability and the extension of the plastic domain are increasing with NaNO2 concentration. (C) 2001 The E lectrochemical Society.