Sintering of Si ₃ N ₄ ‐Y ₂ O ₃ ‐Al ₂ O ₃

Abstract

Sintering kinetics of the system Si 3 N4‐Y2O 3 ‐Al 2 O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si 3 N 4 were studied with additions of 4 to 17 wt% Y 2 O 3 and 4 wt% A1 2 O 3 . Sintering occurs by a liquid‐phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X‐ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ′ ‐Si 3 N 4 and glass or β ′‐Si 3 N 4 , α ′‐Si 3 N 4 , and glass. The compositions and amounts of the residual glassy phases are estimated.