Sintering of ZrB2-based Ceramic Composites Prepared by HP, SPS, HP-HT Sintering Techniques

Ultra-high temperature ceramics (UHTCs) include borides, carbides, and nitrides with melting temperatures above ∼2700⁰C. The UHTCs have been investigated for high temperature applications including thermal protection systems for hypersonic aerospace vehicles. Three types of zirconium boride based systems (monolithic ZrB2, ZrB2 with 2 wt% of SiC and 2 wt% of B4C) were fabricated and compared by a sintering techniques; Hot Press (HP), Spark Plasma Sintering (SPS) and special sintering technique High Pressure-High Temperature (HP-HT) Bridgman type apparatus. The aim of the present contribution was to investigate the comperison of the obtained samples by different techniques. Hot pressing was conducted in the AGH University of Science and Technology. Thermal Technology LLC equipment was used. All samples were sintered in argon flow, the heating rate was 10⁰/min, the soaking time was 30min and applied pressure was 25 MPa. Sample without sintering additives was sintered at 2100⁰C and samples with B4C and SiC were sintered at 2050⁰C. Spark Plasma Sintering was conducted using HPD5 type, FCT system equipment. Samples were sintered in argon, under 35 MPa. The heating and cooling rate was 200⁰/min and soaking time was 10 min. The sintering temperatures were varying between 1700⁰C and 2100⁰C for pure ZrB2 and between 1700⁰C and 2000⁰C for samples with sintering aids. For samples with SiC and B4C additives, higher temperatures were not applied because liquid phase appeared in 2000⁰C and further heating could have cause damage of dye and equipment. In High Pressure-High Temperature (HP-HT) method, the temperature of process was 1900 ± 50⁰C and the pressure 7.2 GPa. After sintering samples were prepared for further investigation by cutting grinding and polishing. Samples achieved using HP-HT method exhibited the highest mechanical properties. The hardness of the monolith was approximately 15,2 GPa which after the SiC addition increased to a value of 18 GPa. The highest hardness was measured for the system ZrB2+B4C with a value of approximately 20 GPa.