3D microstructure and crack pathways of toughened CaO–Al2O3–SiO2 glass by precipitation of hexagonal CaAl2Si2O8 crystal

We investigated CaO-Al2O3-SiO2 glass partially crystallized with molybdenum particles as nucleating agents. Microstructure of the material was characterized as a house-of-cards structure composed of plate-like crystals. Microcracks propagated along the crystal plane parallel to the double layer of SiO4/AlO4 tetrahedrons separated by layers of calcium atoms. To investigate the fracture behavior of the hexagonal CaAl2Si2O8 crystals, molecular dynamics simulations were performed, which demonstrated that a crack can be easily triggered by shear deformation along the calcium layer. Additionally, once a crack was generated in the calcium layer, it propagated rapidly, whereas the crack perpendicular to the calcium layer hardly propagated. This simulated behavior is consistent with the experimentally observed cleavage behavior of the hexagonal CaAl2Si2O8 crystal. The experimental and simulation results effectively explained the non-elastic fracture behavior of the material.