Synthesis of tungsten carbide–nickel composites by the field-activated combustion method

Abstract

The activation of self-propagating combustion reactions in the WC–Ni system was investigated by using an electric field. Self-sustaining combustion in elemental reactants with composition corresponding to WC– x wt.%Ni (0⩽ x⩽10) composites can be activated only when the imposed field is above a threshold value. The nature of combustion products depended on the magnitude of the field. The products contained the high temperature phase (WC), low temperature phase (W 2C) and mixed compounds of type Ni 2W 4C. WC diffraction peaks in X-ray diffraction diagram shifted right when moving from the reactants region to the final product one or increasing electric field. The effect of the relative density of the reactants compact on the synthesis of WC–Ni was also investigated. Moreover, the reaction mechanism of WC–Ni is proposed. X-ray and microscopic analysis of the quenched combustion front suggests that the synthesis of WC is a process involving the solid diffusion of carbon into a carbide layer. Molten Ni reacts with W and W 2C to form intermediate phase, which decomposes into WC and Ni. Molten Ni redounds the transformation from W 2C to WC phase.