Quantitative X-ray diffraction analysis of reactive infiltrated boron carbide-aluminium composites

Dense (> 98% of theoretical) boron carbide, (B4C)-aluminium (Al) composites were produced between 985 and 1370 degreesC by pressureless melt infiltration of Al alloys into porous B4C compacts under. argon (Ar) atmosphere. The microstructure of the composites were investigated using a scanning electron microscope (SEM) and the phases were determined quantitatively by the ratio of slopes method using X-ray diffraction (XRD) analysis. XRD results showed that B4C-Al composites are composed of various combinations of Al3BC, AlB2, AlB12C2 and Al4C3 phases. The type of phases formed and their quantities depend on processing conditions. The AlB2 phase forms at relatively small amounts and its formation can be significantly suppressed or totally eliminated by increasing the particle size of the starting B4C powder and/or altering its surface chemistry. The Al3BC phase, on the other hand, is observed to be the main reaction product forming and is always present in all composites. The other phases, AlB12C2 and Al4C3, are observed to form only at the higher end of the investigated temperature interval. The formation of hygroscopic Al4C3 phase necessitates a prolonged exposure in addition to high temperatures. Coating the surface of the starting B4C powder with SiO2 or passivating reduces the amount of reaction products substantially. Infiltration of B4C by Al is assisted by the formation of Al3BC. (C) 2002 Elsevier Science Ltd. All rights reserved.