Development of HfB2-SiC composites for high-temperature ceramics

The aim of this master thesis is production of HfB2-SiC based ceramics with high density and high thermal, mechanical and oxidation resistance were carried out by applying a single heat treatment using of HfO2, B and SiC starting powders via spark plasma sintering method. In the first stage of the study, the optimum conditions of HfB2 production were determined by the SPS method using HfO2 and B powders. At this stage, two different heating regimes, one step and two step, were applied and the effects of SPS parameters such as heating and cooling rate, pressure, sintering time, hBN coating effect were investigated. In the second stage of the work, HfB2-SiC composites with 30% and 20% SiC contents were produced on the basis of HfB2 production conditions. In addition to SPS parameters, the effect of initial SiC particle size on microstructural, mechanical and oxidation resistance was investigated. FACTSAGE thermodynamic software was used to investigate and eliminate the formation conditions of possible intermediate phases during production. Considering obtained results, it was observed that SiC with fine grain size improved the microstructure and increased the oxidation resistance. It was determined that the mechanical properties of the B4C ternary phase formed when coarse SiC was used and that it increased the densificaiton and had no negative effect on the oxidation. It has been observed that HfB2-SiC composites produced by in situ synthesis show similar thermal conductivity and oxidation behavior with HfB2-SiC composites prepared by conventional methods and have higher mechanical property values and oxidation resistance for some tested samples.