Effects of doping Al2O3/2SiO2 on the structure and properties of magnesium matrix ceramic

• Introducing Al2O3/2SiO2 improve the sintering properties of magnesium matrix ceramic.
• With Al2O3/2SiO2 addition increased, thermal shock times increased significantly.
• Transgranular combining intergranular fractures can eliminate the crack propagation.

To improve the sintering properties and the thermal shock resistance of magnesium matrix ceramic, this work used micron-sized MgO as the main raw material and nano-Al2O3 and SiO2 as additives. Magnesium matrix ceramic was doped with different amounts of Al2O3 and SiO2 (Al2O3 and SiO2 at a molar ratio of 1:2) and sintered under standard atmospheric conditions. The effect of Al2O3/2SiO2 doping amounts on sintering properties, thermal shock resistance, phase composition, and microstructure of composite ceramic materials were investivigated. The results suggested that introducing Al2O3/2SiO2 could improve the sintering properties of magnesium matrix ceramic. The grain boundary migration of its periclase phase could be hindered by the magnesium aluminate spinel and forsterite formed by solid reaction including Al2O3, SiO2 addition, and the MgO itself. Furthermore, according to the mechanism of thermal expansion mismatching, with increasing Al2O3/2SiO2 addition, thermal shock times increased significantly, the number of ceramic internal micro-cracks increased after the thermal shock and the material fracture surface energy was improved. It is found that the way of transgranular combining intergranular fractures can decrease the stress concentration at the crack tips and hinder crack propagation. The secondary phase particles deflected matrix internal micro-cracks and the crack propagation path length thus increased, residual stress field were subjected to interference and energy dissipation mechanisms improved. Meanwhile, thermal shock times for the material were enhanced and the degree of densification increased with increasing sintering temperature.