Balancing transparency with enhanced mechanical properties in MgO-Al2O3-SiO2 glass-ceramics

Transparent glass-ceramics (GCs) are promising for applications that require both optical clarity and superior mechanical strength, such as high-performance displays and ballistic armor. However, achieving this combination typically involves a trade-off, as crystallization processes that enhance mechanical properties often compromise transparency. This study investigates the optimization of mechanical properties in transparent and translucent MgO-Al2O3-SiO2 (MAS) GCs. We examine the heat treatment conditions necessary for achieving various levels of transparency and evaluate the influence of crystal size and volume fraction on Vickers hardness, indentation crack resistance, and fracture toughness (K-Ic). Our findings indicate that, depending on the composition and heat treatment conditions, even nanocrystals smaller than 100 nm can diminish transparency, rendering the GCs translucent. Translucent and opaque samples exhibit superior mechanical performance due to higher crystallized fractions and larger crystals. However, specific thermal protocols were identified to produce transparent GCs (visible light transmittance > 80% for 1.5 mm thick samples) with at least a 30% increase in K-Ic compared to their parent glasses. This study demonstrates the feasibility of balancing transparency and mechanical strength in MAS GCs through careful optimization of processing parameters.