Understanding the effect of surface flaws on the strength distribution of brittle single crystals

Abstract

AbstractThe dependence of strength on the surface quality of brittle single crystals is highly relevant in microelectronic applications, where a certain roughening of the crystal surface is required to guarantee or enhance the functional properties of the final component. In this work, the effect of surface conditioning on the strength distribution of single crystals is assessed on LiTaO3 and LiNbO3 samples with distinct surfaces (i.e., polished, grinded, and scratched). Artificial surface cracks (scratches) were introduced using a Berkovich nanoindenter tip oriented under various angles with respect to the most critical {012} cleavage plane. Biaxial tensile tests were performed using the ball‐on‐three‐balls test, supported by fractographic analyses to interpret the strength results. A direct correlation between sub‐surface damage and strength was observed, associated with the hardness and elastic constants of the material, being strongly dependent on the crystal orientation with respect to the loading axis. Furthermore, we provide an explanation for the usually low Weibull modulus in single crystals and discuss the validity of the biaxial tests on scratched specimens for fracture toughness evaluation.