Effect of Gaseous Hydrogen on Cyclic Slip Behavior around a Stage I Fatigue Crack Tip in an Iron Alloy

摘要

In order to investigate the effect of gaseous hydrogen on cyclic slip behavior around an early stage (stage I) fatigue crack tip, fatigue crack growth (FCG) tests using a single-crystalline Fe-3.2wt.%Si alloy are conducted respectively in a hydrogen atmosphere and in a helium atmosphere. The cross-sectional observations of the crack tips by both electron backscatter diffraction (EBSD) method and transmission electron microscopy (TEM) successfully reveal the following points. In helium atmosphere, FCG is preceded by formation of cell structures and crack propagates along cell boundaries. In hydrogen atmosphere, on the other hand, no cells are seen, and crack growth process is similar to that observed in a stage II type FCG Crack extension resistance in hydrogen is postulated to be lower than that in helium, indicating that the mode of FCG in hydrogen is more critical than that in helium. Stage I fatigue crack growth, Hydrogen embrittlement, Dislocation structures, Single crystal, Iron-