Ultrahigh hardness Li2O-MgO-Al2O3-SiO2 glass-ceramics containing multiphase nanocrystals

Li2O-Al2O3-SiO2-based glass-ceramics containing nanocrystals have attracted much attention due to their low expansion coefficient, good mechanical properties, for different applications, such as fire-safe glass, dental materials, and electronic devices protectors. In current research, ultrahigh hardness Li2O-MgO-Al2O3-SiO2 glass-ceramics were prepared by conventional melt-quenching and subsequent heat-treatment method. MgO was introduced via Li2O substitution to change glass crystallization and mechanical properties. The differential scanning calorimetry analysis indicated the glass transition and crystallization temperatures increased with MgO/Li2O ratio increase, for better glass network connectivity from Raman spectra analysis. In addition, the main crystal phase changed from Li2SiO5 and LiAlSi4O10, to the combination of LiAlSi2O6 and MgAl2Si4O12, and finally to MgAl2Si4O12. The Vickers hardness of glass-ceramics was highly dependent on MgO/Li2O ratios in glass components and heat-treatment temperatures, corresponding with the crystal phases in glass-ceramics. The highest hardness could reach 9.34 GPa, which was much higher than traditional silicate glass-ceramics. The scanning electron microscope images confirmed the crystal diameters that varied from 30 to 100 nm and were determined by MgO content. Transmission electron microscope images and energy-dispersive spectroscopy mapping also confirmed the precipitation of multiphase nanocrystals in glass matrix. The changes of glass structure, and corresponding crystal combinations in glass-ceramics resulting from MgO introduction, were responsible for the ultrahigh hardness glass.