Activated slip systems in β-silicon nitride during high temperature deformation

In order to clarify the activated slip systems of β-silicon nitride (Si₃N₄) during high temperature deformation, we have studied the dislocation structures in hot-pressed β-Si₃N₄ deformed at temperatures from 1820 to 2020 K with strain rates from 9×10^-6 to 2×10^-4 s^-1. Analysis of the dislocations by transmission electron microscopy revealed that the most of dislocations in β-Si₃N₄ plasticaly deformed at high temperatures were c dislocations which were mobile on the {1010} as a primary slip plane. Moreover, a dislocations on the {1010} slip plane were also found to be mobile. The density of a dislocations to that of c dislocations was roughly estimated to be the ratio of 1 : 10, irrespective of the deformation condition. In addition, (a+c) dislocations gliding on the {1121} pyramidal plane were seen to be activated only under the limited deformation conditions at which β-Si₃N₄ showed a fairly good ductility without crack formation. The density of (a+c) dislocations was about two orders of magnitude lower than that of c dislocations.