Atomic picture of crack propagation in Li2O-2SiO2 glass-ceramics revealed by molecular dynamics simulations

Fundamental understanding of the interaction between glass and ceramic phases with a running crack and the mechanisms by which propagation is hindered or altered as compared to the precursor parent glasses remains elusive for the lithium disilicate glass-ceramics. We herein conduct extensive molecular dynamics simulations to reveal some atomic details that are otherwise extremely challenging to be probed by experiments. The results show that the crack propagation pathway in glass-ceramics is dramatically different as compared to the precursor parent glass. In glassy sample, clean crack branching seems to be triggered by multiple cavitation events ahead of crack tip. In glass-ceramic samples, however, branching is characterized by microcracks at multiple glass-nanocrystal interface sites, clean nanocrystal cleavage along certain crystalline plane, and even secondary cracks due to the percolation of multiple microcracks. Additionally, the nanocrystal distribution, total volume fraction, and aspect ratio also have pronounced effects on the propagation of a primary crack and can lead to very diverse crack patterns.