Exceptional Friction Mitigation via Subsurface Plastic Shear in Defective Nanocrystalline Ceramics

Abstract

Single-crystal and microcrystalline ceramics classically fail via brittle fracture under loading. Here, we report that atomic layer deposition {0002}-textured ZnO films, with nanocolumnar grains and defective sub-stoichiometric structure, exhibit nanocrystalline plasticity and exceptionally low sliding friction and wear. These films were tailored to contain low-energy basal stacking fault planes parallel to the film surface. Cross-sectional high-resolution TEM studies inside friction-induced surfaces coupled with density functional theory calculations revealed the fundamental mechanism of this unexpected behavior. We show that sliding on {0002}-textured nanocrystalline ZnO films increases partial dislocation density through intrafilm shear, via glide of partial dislocations, on {0002}-stacking fault planes.