Synthesis of Al2O3-WSi2-WB2-WB composite in Al-Si-WO3-B2O3 system by self-propagating high-temperature synthesis

Abstract

Borides and silicide of tungsten as the refractory intermetallic compounds have high mechanical properties, relatively good thermal shock, and chemical stability. Also, they have less brittleness than ceramic compounds that can lead to its usage in various industrial applications. In this work, for the first time, an alumina-based composite (WB-WB₂-WSi₂-Al₂O₃) was produced by combustion synthesis using aluminothermic reaction of a quaternary mixture (Al-Si-WO₃-B₂O₃) as starting materials. According to standards defined by Merzhanov, Munir, and Anselmi, the combustion synthesis process for the system of Al-Si-WO₃-B₂O₃ is the type of self-propagating high-temperature synthesis (SHS). The milled mixture was formed into cylindrical specimens after cold pressing and was heat-treated using an oxyacetylene flame as the initiator of self-propagating high-temperature synthesis in the air atmosphere. The ignition, the maximum combustion temperature, and the progress speed of the combustion front were measured using several thermocouples and data logger device. The phases formed in the synthesis samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The results showed that the combustion front had a temperature above 1800 °C with a speed of about 20 mm·sec⁻¹. Microstructural observations showed the blades of tungsten borides with a hexagonal structure and spheres of tungsten silicates in the matrix of alumina phase. The average of particle size of borides and silicide of tungsten varies in the range of 100 to 200 nm, indicating the formation of sub-micron composite due to the high speed of the combustion synthesis process.