Mechanical alloying, sintering and characterization of Al2O3–20 wt%–Cu nanocomposite

Alumina-based matrix nanocomposite powder reinforced with 20 wt%-Cu particles was fabricated by mechanical alloying. The starting powders mixture was milled in a planetary ball mill up to 20 h. The effect of milling time on the properties of obtained powders was studied. X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were used to investigate phase composition, crystallite size and morphology of the milled powders. To study the sinterability, the milled nanocomposite powders were cold pressed at 10 MPa and sintered in argon atmosphere at different firing temperatures, i.e. 1100, 1250, 1400, 1500 and 1550 °C, for 1 h. Physical properties, namely, bulk density and apparent porosity of sintered bodies were determined by the Archimedes method. Phase identification and microstructure of the sintered composites were investigated by using scanning electron microscopy (SEM) as well as energy dispersive spectrometry (EDAX). Microhardness and fracture toughness of sintered composite were also examined using Vickers indentor. The results revealed that a uniform distribution of Cu reinforcement in Al2O3 matrix, coating the particles, was successfully obtained after milling the powders. Also, there was no sign of phase changes during the milling. The crystallite size decreased at prolonged milling time while the internal strain increased. The maximum relative density was obtained after sintering at 1550 °C. The hardness of the sintered composite improved while the fracture toughness slightly decreased with the prolongation of milling time.