Critical Depth of Hard Brittle Materials on Nano Plastic Forming

Abstract

This paper reports on ductile to brittle transition of hard brittle materials in nano plastic forming process. Formability of some hard brittle materials, i.e., glasses, silicon and quartz wafers, were examined through a specially designed and developed nano forming tester. A wedge type tool of single crystal diamond was indented to the specimen so that two dimensional plastic deformation was realized. Crack ratio was measured by an optical microscope. Depth of indented grooves were analyzed by FIB machining and SEM observation technique. Based on experimental data, load/depth relationship and the critical depths of hard/brittle materials, at which ductile to brittle transition in deformation occurs, were assessed. The mechanism of ductile-brittle transition is also elucidated by a theoretical model developed based on fracture mechanics. The theory explains that the critical depth depends on the fracture toughness and yield stress of the material, which agrees with experimental results. Effects of microscopical structures of material such as size distribution of micro cracks and anisotropy are discussed.