The effect of annealing temperature on flexural strength, dielectric loss and thermal conductivity of Si3N4 ceramics

Abstract

Effect of annealing temperatures on flexural strength, dielectric and thermal properties of Si3N4 ceramics was investigated with different amounts of Yb2O3 (3.5 mol% and 7 mol%) as sintering additives. High density of >99% were achieved after hot pressing. The post annealing heat treatment promoted the crystallization of the grain boundary glass phase. Low dielectric loss of <4 × 10−4 were obtained for all samples, a low dielectric loss of 1.8 × 10−4 was achieved by annealing at 1500 °C for 24 h with 7 mol% Yb2O3 as sintering additives. A mild anisotropic microstructure was obtained due to merit of hot pressing method. High thermal conductivity of >75 W/(m·K) and >90 W/(m·K) were obtained in the direction parallel and perpendicular to the hot-pressing direction in all samples, respectively. The low flexural strength of ∼600 MPa may attribute to the large grain in the matrix and lack of elongated abnormal grains.