Dislocation motion at a fatigue crack tip in a high-nitrogen steel clarified through in situ electron channeling contrast imaging

The dislocation motion was observed at the tip of a fatigue crack in the high nitrogen steel (HNS) by in situ test through electron channeling contrast imaging. No dislocation motion was observed near the crack tip even at a stress amplitude higher than the fatigue limit. In contrast, dislocation pileup was observed a bit from the crack tip with very narrow dislocation spacing. In addition, with increasing number of cycles, the dislocations were extended to stacking fault. The stacking fault showed a reversible behavior of shrink and expansion, which may influence in enhancing the crack growth resistance of the HNS.