STRUCTURE AND PHASE FORMATION IN BORON CARBIDE AND ALUMINUM POWDER MIXTURES DURING HOT PRESSING

摘要

The paper examines the structure and phase formation during hot pressing of boron carbide powder mixtures containing 20-50 vol. % aluminum and analyzes the microhardness and fracture toughness of the hot-pressed samples. It is established that the particle size of the starting powder has an essential effect on the structure and mechanical properties of boron carbide composites. A matrix structure consisting of aluminum carboboride and borates and inclusions of boron carbide forms during hot pressing of mixtures containing coarse B_4C powder. The microhardness of the matrix varies from 20 to 25 GPa and that of boron carbide grains from 42 to 44 GPa. Homogeneous finegrained structure mainly consisting of aluminum nitride and borates forms in hot-pressed mixtures containing fine boron carbide. Its microhardness is 33-37 GPa and fracture toughness 5.4-5.7 MPa-m~(1/2).