UNDERSTANDING THE EVOLUTION OF DEFORMATION STRUCTURES AT FATIGUE CRACK TIPS AND IMPLICATIONS FOR ENVIRONMENTALLY ENHANCED AND RETARDED FATIGUE CRACK GROWTH

摘要

The corrosion behavior of 300-seriesstainless steel alloys near fatigue crack tips hasbeen extensively studied in relation to howcorrosion may influence environmentallyenhanced and retarded fatigue crack growth.However, examination of the deformationstructures that evolve ahead of fatigue cracktips, and the effect of these structures on boththe cracking behavior and corrosion process, hasreceived less attention. Knowledge of thesestructures, their evolution, and how theyinfluence the corrosion process is essential forthe development of multi-scale models offatigue crack growth. This work reviews thedeformation structures formed ahead of fatiguecrack tips generated in elevated temperature(288°C), high purity water; elevatedtemperature (288°C) air; and ambienttemperature (22°C) deuterium gas to elucidate:(1) how deformation structures evolve withdistance ahead of the crack tip for the differentenvironments, (2) how differences in thedeformed microstructure influence the crackingbehavior, and (3) how fatigue generateddeformation structures impact the corrosionprocess that is observed. Deformation-basedfracture mechanisms which may explain thefracture surface morphology characteristic ofenhanced and retarded fatigue crack growth andthe effect of deformation on corrosion processesare discussed.