Effect of the Structure of Lithium-Silicate Glasses on the Mechanical Properties of Transparent Glass-Ceramic Materials

Abstract

The development prospects of high-strength transparent glass-crystalline materials on the basis of lithium disilicate for protection of optical systems are found to be closely related to their structural features. We formulate the main criteria for the synthesis of transparent pyroceramics, develop model glasses of the R2O–RO–RO2–R2O3–P2O5–SiO2 system with the ratio SiO2/Li2O = 4.0 and produce glass-crystalline materials on their basis under conditions of two-stage low-temperature short-term heat treatment under production conditions. The mechanism of formation of the structure and phase composition of glass-crystalline materials on the basis of model glasses under thermal processing is investigated. The essence of the mechanism consists in the formation of lithium metasilicate nuclei-forming agents in the form of spherulites whose growth is limited by the glass phase distribution, the subsequent growth of needle-like crystals of lithium metasilicates, and their recrystallization into lithium disilicate crystals with a pronounced pseudocubic habitus pattern in the form of crossed needles and proportion of 50 vol.%, which form a layered structure in the form of dendritic needles. It is shown that a certain crystallographic orientation of lithium disilicate crystals ensures the scatter reduction of the material elastic characteristics and provides the elastic modulus as high as 307 GPa, the compressive strength of 650 MPa, and impact strength as high as 5.5 kJ/m2. It was established that the formation of a closed-form mesh block structure on the basis of 0.4 μm lithium disilicate lamellar crystals provides high-strength properties of the developed material, with a transparency in the visible part of the light spectrum, which makes it possible to use this material as the basis for obtaining transparent bullet-proof pyroceramic for the protection of optical devices of military equipment. Investigation of the ballistic stability of the developed pyroceramic and comparison of its physical and chemical properties with other known transparent ceramic high-strength materials proves the expediency of creating high-strength glass-crystalline materials on the basis of lithium disilicate to obtain transparent high-strength components for the purpose of the local protection against high-speed impact action.