Role of surface carbon nanolayer on the activation of flash sintering in tungsten carbide

Flash sintering has been recently successfully activated also in conductive ceramics like tungsten carbide (WC). The present work aims at understanding how the WC particles surface chemistry can influence the electrical properties of the material and play a fundamental role in the flash sintering phenomenon. An electrical contact resistance (ECR) model was developed to understand the role of resistive surface layers on the electrical behaviour of WC green compacts under different applied pressures during the initial stages of the processes. It is established that the large resistivity measured on green compacts can be attributed to the sole presence of an ultrathin carbon layer on the particles' surface. A carbon nanolayer with a thickness of about 1-2 nm, as detected by XPS and TEM analyses, is found to be responsible for the high resistance reached at the particles' contact points while evolving during the flash event. Flash sintering conditions can be achieved during the electrical resistance flash sintering (ERFS) process in WC nanoparticles covered by such carbon layer and independently of the presence of W oxides.