The process of combustion synthesis of WC-Co composites under the action of an electric field

Composites of WC-Co have been synthesized and consolidated simultaneously at the ignition temperature of 794 degrees C by a field-assisted combustion synthesis method (EFACS), where the electric field was generated by a Gleeble thermal simulation instrument. Then, with the aid of high-temperature XRD results, the combustion synthesis process of an 88 wt% (W + C)-12 wt% Co system was studied according to quenching at different temperatures by turning off the electric field. A four-step model describing the process of combustion synthesis of WC-Co composites under an electric field, which is controlled by solid diffusion among the reactant atoms, is proposed. From the preheating period to the solid diffusion period, the solid diffusion among reactant atoms enhance with the increase of temperature. From the solid diffusion period to the combustion period, the 2W((s)) + C-(s) = W2C(s) reaction may occurs at some interfaces between W and C atoms. During combustion period, 2W((s)) + C-(s) = W2C(s) occurs firstly and follows the reaction of W2C(s) + C-(s) = 2WC((s)). Co melts and then reacts to W, W2C in order to form WC and Co3W3C, with that CO3W3C carbonizes to form WC and Co. After the combustion period, the remaining phases of W2C and Co3W3C can be carbonized to form WC with the increase of temperature, and the morphology of tungsten carbide changes from spheroid to polyhedrons as the temperature rises. (C) 2010 Elsevier B.V. All rights reserved.