The effects of straining on oxide films and passivity of copper in nitritesolution at ambient temperature

摘要

The effects of straining on interactions between copper and oxide layer growing on itsrnsurface has been studied. It was shown that the electrochemical oxidation process ofrncopper in NaNO2 solution at room temperature is accompanied with generation of largernamounts of vacancies at the copper-Cu2O interface, at potentials when CuO oxide layerrnstarts to grow on the Cu2O oxide. Diffusive flow of vacancies into the metal orrnannihilation by dislocation reactions is required to continue oxidation with a highrncurrent density. Slow staining results in significant re-arrangements of the dislocationrnstructure, which helps to consume the oxidation generated vacancies. Strain-inducedrncracking of the passive film results in repassivation and, thus, lower oxidation rate thanrnslow straining <10-8/s without film rupture. Without straining oxidation ceases.rnThe influence of electrochemical oxidation on the creep rate of copper at differentrntemperatures in oxidizing environment has been studied. It is shown that excessivernvacancies generated at the stage of CuO oxide layer growth lead to a significant increasernof the creep rate. The phenomenon of plastic bending of thin copper strip during its onesidedrnoxidation was found and studied in detail. It is shown that bending is due tornplastic relaxation of elastic stresses accompanying the rearrangement of dislocationrnassemblies, stimulated by vacancy flow, in a surface layer of copper. The influence ofrnoxidation process on dislocation structures in surface layers of copper is confirmed byrnTEM observations of OFHC and high-purity (99.9999) copper.rnThe obtained results are discussed in connection to a TGSCC model (SDVC, SelectivernDissolution – Vacancy Creep model) related to the electrochemical oxidation of copper.rnIdea of the key influence of vacancies generated in the process of oxidation on stressrncorrosion crack growth under stress is the basis for the TGSCC model development.