Fabrication of Alumina-Based Metal Nanocomposites by Pressureless Sintering and Their Mechanical Properties

The processing conditions to prepare nano-sized Cu and Mo dispersed Al₂O₃ (Al₂O₃/Cu and Al₂O₃/Mo) composites by pressureless sintering were explored. The composite powders of Al₂O₃/Cu and Al₂O₃/Mo were obtained by the hydrogen reduction of Al₂O₃/CuO and Al₂O₃/MoO₃ powder mixtures and consolidated by pressureless sintering using infrared heating furnace with a heating rate of 200 °C/min. SEM and TEM analyses for the composite showed that the nano-sized metal particles were well distributed and situated on the grain boundaries of the Al₂O₃ matrix. The nanocomposites, sintered at 1300 to 1500 °C for 4 min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in Al₂O₃/Cu nanocomposites with sintering additive of 1 wt% MgO. The sintered nanocomposites exhibited the enhanced fracture toughness of above 4.5 MPa·m^1/2, compared with monolithic Al₂O₃. The mechanical properties were discussed in terms of observed microstructural characteristics.