Structure and Phase Formation in Boron Carbide and Aluminum Powder Mixtures during Hot Pressing

Abstract

The structure and phase formation in mixtures of boron carbide and 20–50 vol.% aluminum powders during hot pressing are examined and the microhardness and fracture toughness of hot pressed samples are studied. It is established that the particle size of the starting powders has an essential effect on the structure and mechanical properties of boron-carbide composites. A matrix structure based on aluminum carboboride and borates with inclusions of boron carbide is formed during hot pressing of mixtures with coarse B₄C powder. The microhardness of the matrix varies from 20 to 25 GPa and that of boron carbide grains from 42 to 44 GPa. Uniform fine-grained structure mainly consisting of borates and aluminum nitride is formed in hot-pressed mixtures with fine boron carbide particles. Their microhardness is 33–37 GPa and fracture toughness 5.4–5.7 MPa•m^1/2.