Faceting, Grain Growth, and Crack Healing in Alumina

Reactive molecular dynamics simulations are performed to study self-healing of cracks in Al₂O₃ containing core/shell SiC/SiO₂ nanoparticles. These simulations are carried out in a precracked Al₂O₃ under mode 1 strain at 1426 °C. The nanoparticles are embedded ahead of the precrack in the Al₂O₃ matrix. When the crack begins to propagate at a strain of 2%, the nanoparticles closest to the advancing crack distort to create nanochannels through which silica flows toward the crack and stops its growth. At this strain, the Al₂O₃ matrix at the interface of SiC/SiO₂ nanoparticles forms facets along the prismatic (A) ⟨2̅110⟩ and prismatic (M) ⟨1̅010⟩ planes. These facets act as nucleation sites for the growth of multiple secondary amorphous grains in the Al₂O₃ matrix. These grains grow with an increase in the applied strain. Voids and nanocracks form in the grain boundaries but are again healed by diffusion of silica from the nanoparticles.