Effects of microstructure on the stress corrosion cracking behavior of nickel-aluminum bronze alloy in 3.5% NaCl solution

This work addresses the susceptibility to stress corrosion cracking in 3.5% NaCl solution (simulating seawater) of three differently obtained microstructures of a nickel-aluminum bronze alloy using slow strain rate tensile tests. The results showed that the stress corrosion cracking susceptibility of annealed and normalized alloys increased with the decrease of the strain rate as the metal became more severely corroded and dissolved at the crack tips. The continuous or semi-continuous α + κ_Ⅲ eutectoid structure is sensitive to stress corrosion cracking, resulting in the highest susceptibility of annealed alloy. The thin and overlapped Widmanstatten α grain hinders extension of the cracks and thus decreases the stress corrosion cracking susceptibility of normalized alloy to some degree. The quenched/aged alloy with homogeneous microstructure without α + κ_Ⅲ eutectoid structure and the β' phase exhibits the lowest susceptibility. The stress corrosion cracking process of nickel-aluminum bronze alloys was revealed and is properly explained by the oxide film rupture and anodic dissolution mechanism as well as the hydrogen induced cracking mechanism.