Scientists from Arizonta State University (ASU) have found new data concerning the intergranular stress-corrosion cracking (SCC) of metals.
Intergranural SCC was considered to occur due to simultaneous presence of tensile stress and corrosion. However, the new research suggests that those factors act independently. It is shown that stress and corrosion do not have to act together in order to provoke SCC. Cracking may occur even if corrosion happens first and stress is applied subsequently.
Karl Sieradzki, Professor of Materials Science and Engineering at ASU states: "The finding is the culmination of about 30 years' work on this kind of stress corrosion problem. We now have a view into how new alloys can be designed to avoid this form of stress corrosion-induced failure."
In their investigation, scientists examined the response of a silver-gold alloy in laboratory scale which is representative of significant alloys that are used in constructions (such as stainless steels and nickel-base alloys). When these alloys experience corrosion effects, nanometer sized holes occur inside the corroded layer. According to the research, the most important factor that controls the occurrence of SCC is the adhesion between the corroded layer and the un-corroded alloy.
The team came to the conclusion that simultaneous presence of stress and corrosion exists due to morphology alterations that affect adhesion. Their methods included the utilization of atomic-scale techniques of high-resolution electron microscopy and atom probe tomography. However, if adhesion between the layers is maintained, cracks that initiate in the corroded layer may as well propagate into the uncorroded alloy. Therefore, a crucial component to stress corrosion cracking which is not identified by measurement of corrosion will exist. This effect results in underestimation of the rate of SCC by more than 10 times, researchers state.
Source: Arizona State University