Dislocation structure and activated slip systems in β-Silicon nitride during high temperature deformation

β-Silicon nitride (Si₃N₄) with sintering additives of 5mass% Y₂O₃ and 4mass% Al₂O₃ was deformed by compression at temperatures from 1820 to 2020K and at strain rates from 9×10^-6 to 2×10^-4 s^-1. Dislocation structures were examined by transmission electron microscopy (TEM) to identify the slip systems activated during high temperature deformation. It was found that the high temperature deformation behavior of β-Si₃N₄ depended strongly on the deformation condition. A good ductility as well as 10% in plastic strain occurred without crack formation under the limited condition of higher temperatures and lower strain rates. Both from the Burgers vector analysis using the weak-beam method and from the trace analysis on TEM, most of dislocations operating during deformation were found to be c dislocations belonging to the {101̄0}[0001] primary slip system. In addition to c dislocations, a dislocations on a {101̄0} 〈12̄10〉 prism slip were often observed. However, a+c dislocations on the {112̄1} 〈2̄113〉 pyramidal slip were only activated under the limited conditions where a good ductility had been appeared by compression. It has been considered, therefore, that the occurrence of ductility would be closely related to the activation of the pyramidal slip system.