The brittle-to-ductile transition in pre-cleaved silicon single crystals

Abstract

A series of fracture experiments were carried out at various strain-rates on pre-cracked silicon single crystals between – 196° and 1000°C. The surface energy for cleavage was determined from many tests to be 2500 erg/cm². A transition from pure cleavage to general yielding at the crack-tip was found to occur over several degrees centigrade. The brittle-to-ductile transition was rate dependent and obeyed an activation energy close to that for thermally-activated dislocation glide. A mechanism based on crack-tip blunting through dislocation nucleation and glide was developed to explain the abruptness of the brittle-to-ductile transition. The crack-tip dislocation arrangements were analysed by Lang X-ray topography.