Influences of Cobalt and Zirconia on Microstructural Features and Mechanical Properties of the Al_2O_3/WC Composites

摘要

Alumina (Al_2O_3) is one of the most successful advanced ceramics due to its high hardness, chemical resistance as well as thermal stability under various severe operating conditions. Therefore, the Al_2O_3 and Al_2O_3 matrix composites were generally employed as cutting tool materials. The present work investigates an improvement in fracture toughness of the Al_2O_3-based composites reinforced by tungsten carbide (WC) particles. A change in toughness of the Al_2O_3/WC composites according to the additions of cobalt (Co) or partially stabilized zirconia (PSZ) is also of interest. The 90 wt% of Al_2O_3 and 10 wt% of WC powders, containing various amounts of Co or MgO-doped PSZ (Mg-PSZ), were formed by a conventional uniaxial pressing. The percentages of Co and Mg-PSZ were varied up to 3 and 4.5 wt%, respectively. The specimens were sintered in argon atmosphere at 1600 °C for 2 hours. The sintered specimens were subjected to testing and characterisation. The density was measured by water immersion method. Microstructure and phase analysis were investigated by scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. Vickers indentation technique was used to determine hardness and fracture toughness. Density of higher than 95% of the theoretical values could be achieved in all cases. The hardness values of the WC reinforced Al_2O_3 composites were higher than those of the monolithic Al_2O_3. The hardness of the composites did not change significantly with the Co addition but it gradually decreased with PSZ additions. However, the presence of both Co and PSZ led to slightly higher fracture toughness. The hardness and fracture toughness of the fabricated composites were in the range of 16-18 GPa and 5-8 MPa.m~(1/2), respectively, which were in the same ranges as commercial cutting tools currently used in the market.