Influence of Grain Refinement on Microstructure and Mechanical Properties of Tungsten Carbide/Zirconia Nanocomposites

WC-W₂C/ZrO₂ nanocomposites were synthesized by pressure-less sintering (PS) and spark plasma sintering (SPS) of tungsten carbide/yttria-stabilized tetragonal zirconia, WC/TZ-3Y. Prior to sintering, WC/TZ-3Y powders were totally ball-milled for 20 and 120 h to obtain targeted nano (N) and nano-nano (N-N) structures, indicated by transmission electron microscopy and powder x-ray diffraction (PXRD). The milled powders were processed via PS at temperatures of 1773 and 1973 K for 70 min and SPS at 1773 K for 10 min. PXRD as well as SEM-EDS indicated the formation of WC-W₂C/ZrO₂ composites after sintering. The mechanical properties were characterized via Vicker microhardness and nanoindentation techniques indicating enhancements for sufficiently consolidated composites with high W₂C content. The effects of reducing particle sizes on phase transformation, microstructure and mechanical properties are reported. In general, the composites based on the N structure showed higher microhardness than those for N-N structure, except for the samples PS-sintered at 1773 K. For instance, after SPS at 1773 K, the N structure showed a microhardness of 18.24 GPa. Nanoindentation measurements revealed that nanoscale hardness up to 22.33 and 25.34 GPa and modulus of elasticity up to 340 and 560 GPa can be obtained for WC-W₂C/ZrO₂ nanocomposites synthesized by the low-cost PS at 1973 K and by SPS at 1773 K, respectively.