Mechanistic investigation of the field-activated combustion synthesis (FACS) of tungsten carbide with or without nickel additive

The activation of self-propagating combustion reactions in the W-C system and its composite with Ni as additive was achieved by using an electric field. The reaction mechanisms of Field-Activated Combustion Synthesis (FACS) of tungsten carbide and its composite have been investigated by using sample-quenched method. Through turning off electric field during FACS process, a series of combustion products with different phase compositions have been obtained. Layer to layer X-ray and microscopic analyses of these combustion products across quenched combustion front suggested that the synthesis of WC is a process involving the solid diffusion of carbon into a carbide layer. W₂C is the intermediate phase between WC and reactants (W and C). Metal additive produces liquid phase and accelerates the diffusion between solid reactants (W and C), which facilitates the formation of W₂C and the transformation from W₂C to WC phase. Moreover, melted Ni reacts with W and W₂C to form mixed compounds of type W _x C _y M _z .