PNNL

Abstract

Stress corrosion cracks interact with the microstructure and microchemistry of the material as they propagate through it. Interactions with grain boundaries with modified microchemistry have been studied extensively but interactions with grain boundaries containing particles have not been studied to any extent. A few studies have investigated cracks interacting with chemically active particles but mechanical interactions have been studied primarily in ceraics. However, there have been no studies of cracks interacting with particles that are electrochemically active. Studies of intergranular stress corrosion cracks growing in AA5083 aged to contain b-phase particles at the grain boundary are reported. A special technique to examine the crack tip region of intergranular stress corrosion cracks by high-resolution transmission electron microscopy (TEM) was employed for this evaluation. These studies have shown that for tests in a NaCl + K2CrO4 solution that b-phase particles are converted to Al2O3 particles and that the crack propagates through or around them. Crack propagation does not appear to be impeded by the presence of the particles as evidenced by the high crack velocity and TEM examinations