Dislocation structures around the crack tips of ferritic stainless steel single crystals were observed with electron channelling contrast imaging method. The electron channelling contrast imaging method permitted the observation of dislocations lying near to the surface using a scanning electron microscope. Fatigue crack growth tests were conducted on compact tension specimens having loading axes of [221] and [110] directions. In the specimen having the [110] loading axis at which the fatigue crack having Mode I and II component propagated, a thin band-like structure consisting of dislocation wall array was observed ahead of the crack tip. On the other hand, the dislocation structures around the crack having Mode I and III components could be divided into three regions in the specimen with the [221] loading axis: the cell structure, the dislocation wall structure and the vein structure were observed in order of ascending distance from crack tip. Difference between the dislocation structures near the fatigue cracks could be understood from the crack mode by which edge and screw dislocation emissions from the crack tips were strongly affected.

ECCI Observations of Dislocation Structures Around Fatigue Cracks in Ferritic Stainless Steel Single Crystals. T.Taniguchi, Y.Kaneko, S.Hashimoto: IOP Conference Series - Materials Science and Engineering, 2009, 3[1], 012020