ZHANG Hongling ¹, KONG Linglei ², CAO Bo¹, LIN Quan ¹, LIU Xiaohua ¹, LU Shujuan¹, SHANG Peng ¹, LI Wenjiang ¹, MA Zhiyong ¹, GUO Li¹

(1. GRIRNM Guojing Advanbced Material Co., Ltd., Langfang 065001, Hebei, China; 2. The First Military
Representative Office of Air Force Equipment Department in Beijing, Beijing 100854, China)

Abstract: With the increasing requirements for protective materials, the traditional transparent armors based on bulletproof glass have encountered difficulty in meeting the application requirements, while lighter and thinner ceramic based transparentarmors are gradually becoming the mainstream choice. As a promising candidate of transparent ceramics with excellent performance, MgAl₂O₄ has high mechanical strength, corrosion resistance, wear resistance and thermal shock resistance. The progress in fabrication and characterization of MgAl₂O₄ transparent ceramics in recent years are briefly introduced. Hot pressing sintering combined with hot isostatic pressing post-treatment technology is a commonly used technique to fabricate MgAl₂O₄ transparent ceramics. Meanwhile, particle size of raw materials should be controlled within the appropriate range, while LiF is used as sintering aid. Also, the relationship between microstructure and mechanical properties of MgAl₂O₄ transparent ceramics is summarized. Microstructure has a direct influence on all mechanical properties and hence ballistic performance of the transparent ceramics. Hardness increases with decreasing grain size. The higher the density, the higher the hardness would be. Elastic modulus has no obvious relationship with the grain size, but is directly related to the relative density. The more homogeneous the microstructure, the higher the fracture toughness would be. Finally, the correlation between mechanical properties and armor ballistic properties is analyzed. There is an inverse relationship betweenhardness and fracture toughness. It is suggested that the hardness of armor ceramics is greater than that of projectiles and the fracture toughness should be as large as possible. With increasing elastic modulus, the interaction time between the projectile and the ceramic surface is increased, which enables the ceramics to absorb more energy. High bending strength helps ceramics to withstand multiple projectile impacts. Fracture mode is related to the energy absorbed by the ceramics, whereas transgranular fracture is more desirable than intergranular fracture. Therefore, it is necessary to combine multiple properties to maximize the ballistic performance of transparent armor ceramics.
Key words: magnesia alumina spinel; microstructure; mechanical properties; ballistic performance; transparent armor