Effects of HfB2 addition on the oxidation resistance, microstructure, and mechanical properties of pressureless sintered ZrB2-SiC composite

In order to improve oxidation resistance and mechanical properties of ZrB2-based composites, 10% silicon carbide (SiC) nano-sized particles were used as a reinforcing phase and 4% MoSi2 as a synthesizer aid. In this work, the effects of HfB2 addition (0, 5, 10, 15, 20, and 25%) on Vickers hardness, bulk density, oxidation resistance, and microstructure of the ZrB2-SiC-based ceramics were investigated. The results revealed that the samples consisting of 10% HfB2 have the highest relative density (98.4%). The lowest apparent porosity (i.e., 15%) and the highest hardness (i.e., 15.24 GPa) of the samples were achieved by the addition of 20% HfB2. The X-ray diffraction (XRD) analysis indicated that prolonging the oxidation period resulted in the production of more oxide compounds. The sample containing 25% HfB2 in addition to the lowest relative density due to the oxidized surface erosion and the formation of a poor layer of porous SiC exhibited the maximum oxygen penetration into the sample, the highest gain in mass, and the least oxidation resistance even compared to the ZrB2-SiC composite without the HfB2 addition. It was concluded that by increasing the temperature and time, solid solution formation increases. © 2020 by Begell House, Inc.