Microstructure Investigation of Cu-Ni Base Al₂O₃ Nanocomposites: From Nanoparticles Synthesis to Consolidation

Abstract

Different compositions of Cu-Ni/Al₂O₃ nanocomposites were prepared by a chemical-based synthesis of co-formed oxides (CuO-NiO-Al₂O₃) nanoparticles followed by selective hydrogen reduction of the Cu and Ni oxides and finally by consolidation into pellets. The synthesized composites with both phases (metallic and oxide) containing nanoparticles in the 5 to 60 nm range have been systematically produced. Micro- and nanoscale characterization techniques were extensively employed in all stages of the process. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses have shown a heterogeneous distribution of chemical elements resulting in the formation of Cu- and Ni-rich nanoparticles containing Al₂O₃ phase in a controlled low volume fraction, which later mostly dispersed between the metallic particle and, to a lesser extent, within metallic particles. After consolidation, under uniaxial pressure followed by sintering, the compacted nanocomposite observed in the transmission electron microscope (TEM) revealed that the Al₂O₃ have been more homogeneously distributed as such: the majority of it at the newly formed grain boundaries of the consolidated pellet and a small part of it within the metallic Cu-Ni matrix. Microhardness measurements demonstrate that dispersion of Al₂O₃ was successfully achieved as reinforcement phase, yielding up to 100 pct increase in hardness.