Abstract
The kinetics of stress corrosion (SC) crack propagation in region II of the crack propagation rate versus stress intensity factor curve for AA 7039 has been studied as a function of temperature and sodium chloride concentration using double cantilever beam specimens. Stress corrosion cracking tests were carried out over the range 298–328K in solutions containing 0, 2, and 3·5 wt-%NaCI. Crack propagation rate increased with increasing chloride ion concentration and temperature. Activation energies for theSC crack propagation processes in region II were found to be 32 kJ mol−1 in distilled water and 54 kJ mol−1 in 2·0–3·5 wt-%NaCI solution respectively. The rate controlling steps for SC crack propagation are discussed in terms of anodic dissolution at the crack tip, ion transport within the crack tip solution, creep at the crack tip, and hydrogen diffusion within the metal. From the relation between SC crack propagation rate and stress intensity factor in region II, it is suggested that crack propagation is controlled by hydrogen transport within the metal in sodium chloride solutions, but by cation transport from the crack tip solution to the bulk solution in distilled water.
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