Effect of Halide Ions on Electrochemical Behavior and Stress Corrosion Cracking of 67/33 α-Brass in Aqueous Environments

Abstract

The slow strain rate tension (SSRT) technique was used to study the effect of strain rate on susceptibility to stress corrosion cracking (SCC) and crack velocity of 67/33 α-brass (UNS C26800) in 0.1 M sodium halide solutions (pH = 6.8) at 25°C. The effect of halide ions on electrochemical behavior of α-brass also was investigated using cyclic polarization techniques. Results indicated fluoride ions (F⁻) induced a significant susceptibility to intergranular stress corrosion cracking (IGSCC). Susceptibility increased with decreasing strain rate. Crack velocity also increased with strain rate in a double logarithmic relationship. The entire fracture surface was characteristic of IGSCC at a critical strain rate of 2 × 10⁻⁶/s. The open-circuit potential (OCP) was within the potential range where cuprous oxide (Cu₂O) is stable. Electrochemical polarization analysis confirmed that 67/33 α-brass can form a passive Cu₂O film in 0.1 M sodium fluoride (NaF) solution and that this passive film can break down. Results suggested film rupture and slip-dealloying dissolution may be involved in IGSCC of 67/33 α-brass in F⁻ solution. In 0.1 M chloride (Cl⁻), bromide (Br⁻), or iodide (I⁻) solutions, no SCC susceptibility was observed regardless of strain rate. OCP moved to more active potentials in the presence of Cl⁻, Br⁻, and I⁻. This result was attributed to formation of soluble cuprous complexes controlling the dealloying process through precipitation of metal ion salts on the surface of α-brass.