Mechanical properties, microstructure and grain orientation of hot pressed WB2 ceramics with Co as a sintering additive

Abstract

Abstract Tungsten diboride (WB 2 ) ceramics were hot pressed using Co as a sintering additive at relatively low temperatures ( 2 ceramics. With the addition of Co into the WB 2 matrix, the densification of WB 2 ceramic could be achieved with a high relative density of 92.144% at a temperature of 1500 °C. The sample also exhibited excellent mechanical properties with the flexural strength of 512.7 ± 43.5 MPa, Vickers hardness of 22.4 ± 1.0 GPa and fracture toughness of 4.9 ± 0.3 MPa m 1/2 . The effects of sintering temperature and Co content on the densification, mechanical properties and microstructure development of the ceramic composites were systematically investigated. It suggested that the samples demonstrated a dramatic improvement and then a slight decrease in mechanical properties with the increasing temperature. Additionally, the mechanical properties of the samples decreased gradually with the increase in the mass fraction of Co. Based on the XRD and EDS analysis, Co reacts with WB 2 to form binary and ternary phases during the sintering process, contributing to the densification to a large extent. Besides, the formation of Co 2 B and W 3 CoB 3 also strengthened the binding force at grain boundaries, resulting in the high strength of the samples. Crack propagation path evolved from tortuous to straight with the increasing Co addition, indicating the fracture toughness of the samples decreased gradually. Additionally, the fracture behaviours and toughening mechanisms of the Co-doped WB 2 ceramic composites were also discussed. It is noteworthy that the hot pressed composites exhibited an anisotropy structure to some extent, and the growth and alignment mechanism of hexagonal WB 2 grains was illustrated in this paper.