Samples of β-phase material which contained sintering additives (5wt%Y2O3, 4wt%Al2O3) were deformed in compression at 1820 to 2020K, using strain rates ranging from 9 x 10-6 to 2 x 10-4/s. The dislocation structures were studied by using transmission electron microscopy to identify the slip systems which were active during high-temperature deformation. It was found that the high-temperature deformation depended strongly upon the deformation conditions. Good ductility, and 10% plastic strain, occurred without crack formation under conditions of high temperature and low strain-rate. From a Burgers-vector analysis using the weak-beam method, and from trace analysis via transmission electron microscopy, most of the dislocations which were operative during deformation were found to be c dislocations which belonged to the {10▪0}[00▪01] primary slip system. In addition to c dislocations, a dislocations on a {10▪0}<1¯2▪0> prism slip were often observed. However, a+c dislocations on the {11▪1}<¯21▪3> pyramidal slip system were activated only under conditions where good ductility had appeared during compression. It was concluded that the occurrence of ductility was closely related to activation of the pyramidal slip system.

Dislocation Structure and Activated Slip Systems in β-Silicon Nitride during High Temperature Deformation. K.Kawahara, S.Tsurekawa, H.Nakashima: Key Engineering Materials, 2000, 171-174, 825-32