Stress Corrosion Cracking of 70/30 Brass in Acetate, Formate, Tartrate, and Hydroxide Solutions

It has been shown that stress corrosion cracking can be induced in 70/30 brass by solutions of sodium acetate, formate and hydroxide, and by a tartrate solution, of which only the latter has previously been reported as a potent environment for the cracking of brass. The stress corrosion cracking tests were conducted after predicting that the solutons would cause cracking on the basis of potentiokinetic polarization curves; there was reasonable correlation between whether or not cracking did occur and whether or not it was predicted, as solution compositions and pH’s were varied. Accurate prediction of the potential range for cracking in the various solutions was better achieved with rapid straining electrode experiments than with potentiokinetic measurements, although the latter were useful in giving the first indication of whether or not cracking was likely and may therefore be used for giving a relatively quick indication of whether or not a given environment is potent. When the cracking data from the tests conducted in all of these solutions is plotted upon a potential-pH diagram, it is apparent that intergranular cracking occurs within those ranges of potential and pH wherein Cu₂O is the stable phase, with transgranular cracking at potentials above the Cu₂O domain irrespective of the stable phase, until the potentials reach sufficiently high values for failure by pitting or more general corrosion.