Influence of MgO–SiO₂–CeO₂sintering additives on the sintering behavior and grain boundary structure of Al₂O₃ceramics

In this study, MgO, SiO₂, and CeO₂were employed as sintering aids, and the phase composition, microstructure and grain boundary structure of the Al₂O₃ceramics were characterized via XRD, SEM, and TEM. The sintering behavior and mechanical properties of the ceramics were systematically investigated and analyzed. The addition of sintering aids significantly increased the size of Al₂O₃grains. Excessive CeO₂addition resulted in the appearance of coarse CeAl₁₁O₁₈ s-phase particles in the microstructure. TEM revealed three different types of grain boundaries: clean grain boundaries, grain boundaries with thin intergranular films, and grain boundaries with thick wetting glass films. In the samples with sintering aids, the grain boundaries were predominantly composed of wetting glass films, facilitating sintering densification and leading to grain growth. The addition of CeO₂promoted the crystallization of the grain boundary glass phase, resulting in the precipitation of the crystalline phase Ce₂O₃and thereby enhancing the mechanical properties of the ceramics. The synergistic effect of MgO, SiO₂, and CeO₂significantly improved the sintering behavior of Al₂O₃. At 1600 °C, the samples with 3 wt% MgO, 3 wt% SiO₂, and 1 wt% CeO₂achieved the optimal comprehensive performance, with a relative density of 97.5 %, a hardness of 16.9 GPa, and a compressive strength of 1545 MPa.