Influence of TiO2 contents and sintering temperature on the microstructure and mechanical properties of WC-Al2O3 cemented carbide reinforced by multi-wall carbon nanotubes

WC-30 vol% Al2O3-0.5 wt% CNTs (WAC) cemented carbides with TiO2 as additives were consolidated by high energy ball milling and hot pressing the as-milled composite powders. The effects of TiO2 contents on the microstructure and mechanical properties of the obtained WAC cemented carbides were investigated. The presence of moderate TiO2 refined the grain sizes of WC, which contributed to the increase of relative density, hardness and fracture toughness. However, excessive TiO2 (surpassed 2 wt%) leaded to the increase of grain sizes and the production of new tialite (Al2TiO5) phase, which deteriorated the properties like relative density as well as hardness. While, the fracture toughness values still increased from 7.41 MPam1/2 (0 wt%TiO2) to 7.85 MPam1/2 (3 wt%TiO2) owing to the presence of second phase Al2TiO5. Furthermore, the effect of sintering temperature on microstructure and mechanical properties of WAC cemented carbides with different contents of TiO2 were also examined. Results showed that by increasing TiO2 contents, sintering temperature of the WAC with optimum hardness and fracture toughness shifted to low values. And the maximum values of hardness and fracture toughness for the component of WAC-6 wt% TiO2 sintered at 1440 °C was comparable to the optimal hardness and fracture toughness for WAC-2wt% TiO2 sintered at 1540 °C. According to the investigation results of the selected WAC-6wt% TiO2 composites, the grain growth of WC particles was hindered by the decrease of sintering temperature, resulting in the enhancement of mechanical properties despite of the slightly decreased relative density.