Intragranular plasticity of beta Si3N4 between 20 degrees C and 700 degrees C

Intragranular plasticity induced by indentation is studied in beta Silicon Nitride between room temperature and 700 degrees C by Transmission Electron Microscopy (TEM). It is shown that all the dislocations resulting unambigu ously from plastic deformation have a Burgers vector b = [0001] and a domin ant screw character. This can account for a large Peierls stress along the [0001] direction and a larger mobility of edge dislocation segments as comp ared to screw ones. Dislocations bowing out of screw direction are found to glide in {10 (1) over bar 0} prismatic planes. Cross-slip is evidenced fro m the dislocation microstructure observations. It is found to occur between {10 (1) over bar 0} prismatic planes at 20 degrees C whereas {11 (2) over bar 0} is found to be a new deviation plane at 700 degrees C. Those observa tions are discussed in relation with the possible core structure of [0001] screw dislocations.