Strength Limiting Surface Damage in Single-Crystal Sapphire Imaged by X-Ray Topography
David R. Black
X-ray diffraction topography has been used to investigate the relationship between sub-surface damage and fracture strength in sapphire modulus of rupture (MOR) bars. The bars were indistinguishable using standard optical characterization techniques, but x-ray diffraction topography revealed that they were of two distinct types. The first type had an oriented microstructure consisting of a pattern of linear features running the length of the bars. This microstructure was attributed to fabrication damage. The second type was typical of well-polished, damage-free sapphire. Fracture strength data showed that the damaged bars had strengths less than 70 % of the bars without damage.