Intrinsic Fracture Planes of Sapphire

Abstract The study of fracture characteristics in sapphire crystals (α-Al2O3) is both fascinating and crucial for understanding the failure behavior of this material in relevant applications. However, current conclusions regarding the slip and fracture features of sapphire remain fragmented and unsystematic, particularly concerning the latter. A simple and effective method applicable to structurally similar crystals was proposed in this research: utilizing spatial geometry theory to reconstruct the spatial positions of cleavage planes within crystals through nanoindentation and scanning electron microscopy data. By applying this geometric analysis method to the nanoindentation test results of five typical crystal planes (C, A, M, R, N), information regarding the locations of sapphire’s intrinsic fracture planes and slip planes at room temperature was systematically obtained: (1) within a single unit cell, all six pyramidal planes are cleavage planes: (112̅4), (112̅6), (112̅12), (11̅02), (11̅03), and (11̅06); (2) the C-plane appears to act as the sole slip plane induced by nanoindentation testing at room temperature; no cleavage behavior was observed on this plane.