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.
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