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

Abstract

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.

Molecular dynamics investigation of the fracture mechanism of a glass‐ceramic containing cleavable crystals

“…The fracture simulation has demonstrated that the crack cannot propagate along the notch direction, while the crystal specimen obviously shows slip dislocation along a calcium layer. 21 The same phenomenon is observed even in the glass/crystal composite model in this work.…”

“…Composition of the SiO 2 -Al 2 O 3 -CaO parent glass experimentally studied is (SiO 2 ) 58.8 (Al 2 O 3 ) 12.6 (CaO ) 23.8 . 21 Assuming that 30% mole ratio of h-CAS is precipitated as experimentally measured, the glass matrix composition amounts to (SiO 2 ) 62.6 (Al 2 O 3 ) 7.3 (CaO) 30.1 . We firstly prepared a model for the glassy phase using the usual meltquench method described as follows: A random configuration of 25 003 atoms was melted at 3500 K for 500 ps and was subsequently cooled down monotonically to 300 K with a quenching rate of 1 K/ps.…”

“…Recently, a novel glass-ceramics composed of a SiO 2 -Al 2 O 3 -CaO parent glass and hexagonal plate-shape CaAl 2 Si 2 O 8 crystals (h-CAS), which is a metastable crystal, was found, 19,20 and it was demonstrated that the fracture toughness is improved by the partial crystallization. 21 Since the h-CAS has a layered structure consisted by tetrahedral SiO 4 /AlO 4 oxide layers and two-dimensional sheet-shaped calcium layers, the precipitate forms plate-like cleavable facet as mica 22 (Figure 1). Our recent study has revealed that the plateshape hexagonal crystals crossover each other and develop a house-of-cards-like 3D microstructure, and most of the microcracks have been observed at the interface between the glass matrix and the hexagonal crystals by indentation experiment.…”

“…Our recent study has revealed that the plateshape hexagonal crystals crossover each other and develop a house-of-cards-like 3D microstructure, and most of the microcracks have been observed at the interface between the glass matrix and the hexagonal crystals by indentation experiment. 21 Besides the experimental observation of the microstructure, molecular dynamics (MD) simulations of h-CAS have been conducted to clarify fracture patterns of the crystal using single-notched models, and the following features have been discussed. 21 One is that the calcium layer is obviously cleavable layer when mode I fracture appears, so that a crack can propagate along the calcium layer promptly.…”

“…21 Besides the experimental observation of the microstructure, molecular dynamics (MD) simulations of h-CAS have been conducted to clarify fracture patterns of the crystal using single-notched models, and the following features have been discussed. 21 One is that the calcium layer is obviously cleavable layer when mode I fracture appears, so that a crack can propagate along the calcium layer promptly. The other finding is that a crack perpendicular to the SiO 4 /AlO 4 oxide layer and the calcium layer is prevented to propagate even from the notch tip and induces shear dislocation along the calcium layer in the crystal, even if uniaxial tensile loading is applied.…”