Macroscopic strength and failure of dislocation-engineered MgO

Dislocations in ceramics can enhance mechanical performance and functional properties. Recently, tailoring the dislocation density in ceramics at meso/macroscale at room temperature was made available through a surface scratching technique. The effects of this treatment on the material’s hardness, crack-initiation/propagation and microscopic strength were investigated, with an observed toughening effect. Here we investigated the impact of dislocation density, tuned via surface scratching technique, on the macroscopic strength of MgO crystals. Specimens with three different dislocation densities were tested: unaltered as-received state (<10$^{12}$ m$^{−2}$), an intermediate density (∼10$^{14}$ m$^{−2}$), and a high density (>10$^{15}$ m$^{−2}$). The macroscopic strength was assessed using Ball-on-Three-Balls-tests and Ball-on-Ring-tests. The influence of anisotropic material properties on the stress field and the susceptibility to specimen edge failures was assessed through Finite Element Analysis. Extensive fractographic analysis suggests the observed decrease in the macroscopic strength can be related to the creation of local stress concentrations during dislocation engineering.