TANG Yong 1, XIA Peizong 1, GAO Cundong 1, WANG Weidong 1,
ZHANG Chao 1, GAO Cunji 1, HE Yongtao 2, HUANG Xinhua 2
(1. Shandong Jingyao Glass Group Co., Ltd., Linyi 276624, Shandong, China; 2. Jingdezhen Ceramic University,
Jingdezhen 333403, Jiangxi, China)
Extended abstract:
[Significance] Lithium disilicate glass-ceramics possess the highest known flexural strength to date, along with excellent optical properties and promising biocompatibility. They have been widely used in dental restoration, photosensitive materials, and magnetic disk substrates and so on. Compared with traditional dental restorative materials, they exhibit significant advantages in aesthetic effects, mechanical properties and fabrication processes, making them one of the most promising candidates for dental restoration. Systematic study on their microstructure, mechanical properties and reinforcement technologies is of great importance for promoting theoretical development and practical application of high-performance glass-ceramics.
[Progress] Regarding chemical composition, the addition of Al2O3 and K2O eliminates immiscibility, improving glass homogeneity and chemical stability. Alkaline earth metal oxides, such as ZnO, MgO and CaO, act as network modifiers, influencing crystal morphology and mechanical strength. Rare earth oxides, like Y2O3 and La2O3, serve as network former and can inhibit crystallization. P2O5, TiO2 and ZrO2 act as nucleating agents, providing heterogeneous nucleation sites and promoting the precipitation of Li2Si2O5 crystals. In terms of heat treatment processes, multi-step schedules (e.g., two-step and three-step methods) effectively regulate the crystal phase, grain size, crystal aspect ratio and degree of crystallinity, resulting in an interlocking acicular microstructure with significantly enhanced mechanical strength. Regarding mechanical reinforcement techniques, zirconia toughening utilizes the volume expansion and microcrack dispersion associated with the tetragonal-to-monoclinic phase transformation of ZrO2. Ion exchange strengthening replaces Li+ with larger ions, such as Rb+ and Cs+, generating a compressive stress layer on the surface and hence increasing the flexural strength from 169 MPa to 493 MPa. Physical tempering introduces compressive stress on the material surface through rapid cooling (e.g., oil quenching), increasing the flexural strength from 287 MPa to 576 MPa and the fracture toughness from 2.03 MPa·m1/2 to 4.02 MPa·m1/2.
[Conclusion and prospects] Lithium disilicate glass-ceramics exhibit excellent mechanical properties, due to their acicular interlocking microstructure and the residual compressive stress arising from thermal expansion mismatch between the crystals and the glass phase. It is found that optimizing chemical composition and heat treatment processes enables effective regulation of structure and properties, while there are three reinforcement techniques, i.e., zirconia toughening, ion exchange strengthening and physical tempering, can be used to significantly enhance mechanical strength. These glass-ceramics will have broad applications in the fields, such as bone joint repair, high-end tableware, building materials and electronic mobile device back panels. Future research should be focused on three aspects, including developing low-cost fabrication technologies to expand application scope, exploring anion modification approaches such as nitrogen and fluorine to further improve performance and conducting in-depth exploration of novel reinforcement processes, particularly physical tempering using different cooling media.
Key words: lithium disilicate; glass-ceramic; microstructure; mechanical properties; strengthening techniques