MECHANICAL ALLOYING, SINTERING AND CHARACTERISATION OF Al2O3-20 WT%-Cu NANOCOMPOSITE

Alumina-based matrix nanocomposite powders reinforced with 20 wt%-Cu particles were fabricated by mechanical alloying. The starting powder mixture was milled in a planetary ball mill for up to 20 h. The effect of milling time on the properties of obtained powders was studied. XRD and TEM were used to investigate phase composition, crystallite size and morphology of the milled powders. To study their sinterability, the milled nanocomposite powders were cold pressed at 10 MPa and sintered in an argon atmosphere at different temperatures, i.e. 1100, 1250, 1400, 1500 and 1550 C, for 1 h. The physical properties, bulk density and apparent porosity, of the sintered bodies were determined by the Archimedes method. Phase identification and the microstructure of the sintered composites were investigated using SEM and EDAX. The microhardness and fracture toughness of the sintered composites were also examined using a Vickers indentor. The results revealed a uniform distribution of Cu reinforcement in the Al2O3 matrix, coating the particles, was achieved after milling the powders. There was no sign of phase changes during the milling. The crystallite size decreased after prolonged milling time while the internal strain increased and a maximum relative density was obtained after sintering at 1550 C. The hardness of the sintered composites improved while the fracture toughness slightly decreased with prolonged milling time.