Mechanistic investigation of the field-activated combustion synthesis of tungsten carbide with or without cobalt added

Abstract

The activation of self-propagating combustion reactions in the system of tungsten and carbon and its composites with cobalt as additive was achieved using an electric field. The reaction mechanism of Field-Activated Combustion Synthesis (FACS) of tungsten carbide and its composites has been investigated using the quenching sample method. By turning off the electric field during FACS, a series of combustion products with different phase compositions has been obtained. Layer to layer X-ray and microscopic analyses of these combustion products across the quenched combustion front suggest that the synthesis of WC involves the solid-phase diffusion of carbon into a carbide layer. W 2C is the intermediate phase between WC and the reactants (W and C). A metallic additive produces liquid phase and accelerates the diffusion of the solid reactants (W and C); this facilitates the formation of W 2C and the transformation of W 2C to WC. Moreover, molten Co reacts with W and W 2C to form mixed compounds of type W xC yCo z.