Characterization of Crack-tip Dislocations and Their Effects on Materials Fracture

Three-dimensional structure of crack tip dislocations were investigated by combining scanning transmission electron microscopy (STEM) and electron tomography (ET) in silicon single crystals. P-type (001) silicon single crystals were employed. < 110 > cracks were introduced from an indent on the (001) surface. The specimen was heated at 873K in order to introduce dislocations at the crack tips. The specimen was thinned to include the crack tip in the foil by an iron milling machine. STEM-ET observation revealed the three-dimensional structure of crack tip dislocations. Their Burgers vectors were determined by using an invisibility criterion. The local stress intensity factor was calculated using the dislocation characters obtained in the observation in this study, indicating that the dislocations observed were mode II shielding type dislocations.