Size-dependent mechanical properties and failure study of nickel nanoparticles

Abstract

The limited number of studies that focus on the size-dependent failure mechanisms of individual nanoparticles and their significance on epoxy composite material properties led to the twofold aim of this research: study the failure modes of nickel nanoparticles and determine the dependence of the mechanical properties of the Ni-epoxy composite on the size of the nickel particles used as reinforcement. Samples of spherical nickel nanoparticles were separated by size based on their densities and the resulting sections used as reinforcement in epoxy composites. The microstructural characterization of the nickel samples were performed on a Scanning Electron Microscope and the mechanical properties of the different Ni-epoxy composite pucks investigated using a nanoindenter. For the failure analysis investigation, an ultrasonic processor was used to induce damage to nickel nanoparticles of diverse sizes dispersed in a solvent. The corresponding effects of the treatment on the nanostructures were analyzed through X-ray diffraction techniques, to determine possible phase transformations, and Transmission Electron Microscopy, to analyze changes in the crystal lattice. Findings indicate that the hardness and Young’s Modulus values for the Ni-epoxy composites increase as filler particle size decreases and follows a normal Hall-Petch relation. The intense energy imparted by the ultrasonic process, along the particle-solvent interface, created a protective NiO coating in the Ni spherical nanoparticles. The latter seems to suppress the complete fracturing of the particle despite the creation of multiple lattice defects.