Pressureless sintering and tribological properties of WC-ZrO2 composites

In a recent work [Basu, B., Lee, J. H. and Kim, D. Y., Development of WC-ZrO2 nanocomposites by spark plasma sintering. J. Am. Ceram. Soc. 2004 87(2), 317-319], the processing of ultrahard WC-ZrO2 nanocomposites using spark plasma sintering is reported. In the present work, we investigate the processing and properties of WC-6 wt.% ZrO2 composites, densified by pressureless sintering route. The densification of the WC-ZrO2 composites was performed in the temperature range of 1500-1700 °C with varying time (1-3 h) in vacuum. The experimental results indicate that significantly high hardness of 22-23 GPa and moderate fracture toughness of ∼5 MPa m1/2 can be obtained with 2 mol% Y-stabilized ZrO2 sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC-ZrO2 composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. A transition in friction and wear with load is noted. The dominant mechanisms of material removal are tribochemical wear and spalling of tribolayer.