Damage resistant and tolerant glass-ceramics with low-thermal expansion crystals

Crack initiation and growth limit the mechanical reliability and industrial applications of oxide glasses. The conversion of glasses into glass-ceramics can help to compensate for this shortcoming, as the presence of crystals can cause crack deflection and crack bridging and then increase the fracture toughness. However, due to the different thermal expansion of crystal and glass phases, the generation of residual stress is inevitable, which will induce compressive or tensile stress in glass-ceramics, thus changing the crack propagation path and crack initiation resistance. As such, it is a challenge to simultaneously improve the fracture toughness and crack initiation resistance. In this work, we attempt to address this challenge by modifying the crystal content in Nb₂O₅-doped magnesium aluminoborate glass-ceramics to improve crack resistance. Due to the generation of Al₄B₂O₉ crystals with a lower coefficient of thermal expansion compared to the glass matrix, compressive stress is generated on the surface of the glass-ceramics, which reduces the cracking probability. At the same time, the presence of crystals causes crack deflection and crack bridging phenomena, enhancing the fracture toughness. In addition, heat-treatment also leads to an increase in the network connectivity of the glass ceramics, contributing to the improvement of its overall mechanical properties.