The consolidation of SiC ceramics using MAX phases as a new family of sintering activators

WOZNIAK J. ¹, PETRUS M. ¹, CYGAN T. ¹, OLSZYNA A. ¹

¹ Faculty of Materials Science and Engineering Warsaw University of Technology, Warszawa, Poland

Non-oxide ceramic materials, like silicon carbide, tungsten carbide, or silicon nitride, show several unique properties compared to other materials. They exhibit fascinating properties, including high melting temperature, extraordinary hardness, exceptional stiffness, high resistance to chemical agents, and stability of their properties over a wide temperature range. Unfortunately, achieving full dense ceramic sinters is difficult due to their strong covalent bond, low grain-boundary diffusion coefficient, and the inevitable presence of oxide contaminations on the raw materials. Consequently, it is necessary to apply high processing temperatures, high pressure, novel sintering technique, or the use of sintering aids. Another of their disadvantages, significantly limiting the application potential, is the low fracture toughness. One of the methods of increasing fracture toughness is the production of ceramic matrix composites. The ideal material to act as a reinforcement should improve fracture toughness without reducing other properties, such as hardness or thermal stability. One of the latest trends in research on the production of dense ceramic sinters with high mechanical properties is the simultaneous use of novel sintering techniques combined with the use of a new group of sintering aids. The new group of sintering additives uses the phenomenon of decomposition of the phases used to produce compounds responsible for the intensification of sintering processes and also playing the role of reinforcing phase. One such material group is the MAX phases, which have been gaining popularity recently. During their decomposition, products are formed that react with oxides on the surface of ceramic particles, modifying the sintering process through transient plastic phase processing and introducing the liquid phase sintering (LPS). So far, the influence of the Ti3AlC2 phase on the sintering process of such TiB2, B4C, and ZrB2 materials has been described. It has been shown that the sintered temperature is reduced with a simultaneous improvement in mechanical properties.

Moreover, the world literature lacks research on the influence of MAX phases on other ceramic materials, such as SiC, WC, or Si3N4. Their use has potentially many benefits. It will enable sinter production with high mechanical properties while significantly reducing the sintering temperature. It will also allow for greater control and the possibility of designing the microstructure. The scientific goal is to provide new knowledge on MAX phases, which simultaneously act as a sintering additive facilitating the densification process and as a precursor for the formation of a reinforcing phase. The SiC+xTi3AlC2 composites were produced (x= 2.5-20 vol. % with step 2.5). The influence of the MAX phases on the degree of sinter consolidation, as well as the mechanical properties of the sinter (i.e., hardness, fracture toughness), was tested. In addition, the sinters were subjected to microstructure analysis using SEM and HRTEM microscopy).

Keywords: Sintering, Spark Plasma Sintering, hard-to-sinter ceramic, MAX phases, silicon carbide