PROPERTIES AND MICROSTRUCTURE OF ALUMINA-NIOBIUM NANOCOMPOSITES MADE BY NOVEL PROCESSING METHODS

摘要

Alumina-niobium nanocomposites have been fabricated using high-energy ball milling and electric field assisted sintering (EFAS) or high pressure sintering (HPS). The 10 volume percent niobium nanocomposites have fracture toughnesses greater than 6 MPa√m with only a marginal decrease in hardness. This is nearly twice as tough as a pressureless sintered composite of the same composition reported in work by Garcia et al [1]. This increase in toughness can be attributed to the novel microstructure in the nanocomposites. The present study shows a metallic phase distribution of ～20 nm particles along with a continuous 3-4 nm layer at boundaries between alumina grains. This microstructure should lead to toughening by increasing ductility at the crack tip instead of the traditional ligament bridging in the crack wake which is typical of micron-scaled metallic-phase toughened ceramics.