Effect of Milling Time on the Microstructure and Mechanical Properties of HfB2-ZrB2-TiB2 Sintered via SPS

The aim of this research was to investigate the effect of milling time on the properties of HfB2-ZrB2-TiB2 ceramic. For this purpose, HfB2, ZrB2, and TiB2 powders with equal volume ratios were ground for 15, 30, and 45 hours and sintered using spark plasma sintering method at 2000 °C. X-ray diffraction was employed for phase identification. Microstructural studies were performed using a scanning electron microscope. The hardness and fracture toughness of the samples were evaluated using the Vickers hardness test and crack length measurement, respectively. The X-ray diffraction results of the ground powders showed that the size of the crystallites decreased from 106.9 nm to 59.2 nm with increasing the grinding time from 15 to 45 hours. As a result of sintering process, the number and intensity of the peaks decreased significantly indicating the reduction of oxide impurities and the formation of a solid solution. Increasing the milling time led to the formation of further solid solution. The maximum values ​​of relative density, hardness, and fracture toughness in the sample milled for 45 hours were obtained to be 99.8%, 27.3 GPa, and 5.5 MPa.m0.5, respectively.