Densification and microstructure development in spark plasma sintered WC-6 wt% ZrO2 nanocomposites

In this paper, we report the results of a transmission electron microscopy investigation on WC-6 wt% ZrO2 nanocomposite, spark plasma sintered at 1300 degrees C, for varying times of up to 20 min. The primary aim of this work was to understand the evolution of microstructure during such a sintering process. The investigation revealed the presence of nanocrystalline ZrO2 particles (30-50 nm) entrapped within submicron WC grains. In addition, relatively coarser ZrO2 (60-100 nm) particles were observed to be either attached to WC grain boundaries or located at WC triple grain junctions. The evidence of the presence of a small amount of W2C, supposed to have been formed due to sintering reaction between WC and ZrO2, is presented here. Detailed structural investigation indicated that ZrO2 in the spark plasma sintered nanocomposite adopted an orthorhombic crystal structure, and the possible reasons for o-ZrO2 formation are explained. The increase in kinetics of densification due to the addition of ZrO2 is believed to be caused by the enhanced diffusion kinetics in the presence of nonstoichiometric nanocrystalline ZrO2.