The evolved microstructure ahead of an arrested fatigue crack in Haynes 230

The dislocation microstructure beneath surface slip traces produced by fatigue loading of Haynes 230 was revealed to be a function of distance from a crack tip. The microstructure beneath these traces evolves from planar slip bands with increasing dislocation density and decreasing interband spacing as the crack tip approaches one of refined subgrains and lamellar bands at and in the vicinity of the crack tip. Similarly, beneath fatigue striations the microstructure evolves from nanosized subgrains to a banded structure with increasing distance from the fracture surface. These structures are significantly different to those predicted to develop under fatigue loading of a planar slip material. The evolved structures are considered in terms of the microstructure generated by severe plastic deformation.

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