Direct evidence for dislocation-free zone in Fe–5% Si fractured by Charpy impact test

Defect structure in the subsurface region below a fracture surface of an Fe–5% Si specimen that had been fractured by a Charpy impact test at 77 K was examined by transmission electron microscopy. The specimen was fabricated by a focused ion beam technique to enable analysis of areas that had been carefully selected on the basis of observation. Near the nucleation site of the crack, many dislocations were observed just beneath the fracture surface. Far away from the nucleation site, no dislocations at all were observed in the subsurface region of the fracture surface. Between these two extreme positions, a dislocation-free zone was observed.