THE EFFECT OF SiO2 AND B2O3 ADDITIVES ON THE MICROSTRUCTURE AND HARDNESS OF HOT-PRESSED BORON CARBIDE

Boron carbide (B4.3C) is an attractive material for armor applications due to its low density and high hardness. Unfortunately, because of its atomic bonding, crystal structure, and microstructure, B4.3C is not only very brittle, but also has been shown to be susceptible to stress-induced solid-state amorphization (SSA) and shear localization. Low fracture resistance, stress-induced SSA, shear localization, and perhaps melting are believed to be responsible for B4.3C's loss in shear strength above its Hugoniot Elastic Limit and its poor performance against certain ballistic threats. Consequently, there is strong interest in improving B4.3C's resistances to fracture and shear localization. Limited work on other armor ceramics has shown that those with engineered grain boundaries not only possess higher fracture toughness values, but are also resistant to shear localization. In this investigation, initial attempts to engineer the grain boundaries of B4.3C are reported. Precursors for SiO2 and B2O3 were added to B4.3C powders and ultrasonically mixed. The SiO2/B2O3 ratio was varied and the total additive content was chosen to be 5 v/v.%. The resulting powders were consolidated by hot-pressing under vacuum. The effect of the additives on the resulting densities, phases, microstructures were investigated. Experimental procedures and results will be presented.