In situ formation of Si3N4–SiC nanocomposites through polymer-derived SiAlCN ceramics and spark plasma sintering

Abstract In this paper, fully dense Si3N4/SiC nano-composites were fabricated through polymer-derived ceramics (PDCs) method and spark plasma sintering technique. Polymer-derived SiAlCN ceramic was synthesized by using polysilazane as preceramic precursor, aluminum tri-sec-butoxide as Al source. Then Si3N4/SiC composites with nanometer sized Si3N4 and SiC phases were formed spontaneously during spark plasma sintering through in-situ phase separation of amorphous SiAlCN ceramics. It's found that with the increasement of Al contents, the densification rate was accelerated significantly and serious degradation of Si3N4 phase was avoided by restricting carbothermal reaction. At the same time, Al contained composites show excellent oxidation/corrosion resistance at 1350 °C and 50% H2O - 50% O2 water vapor environment than that of Al free samples. The Si3N4/SiC composites derived from Al contained PDCs overcomes the trade-off between abnormal grain growth and serious degradation of Si3N4 phase, which is a very tough problem for traditional PDC route (without Al) to fabricate Si3N4/SiC composites. For traditional PDC route, (I) if with traditional sintering additives, abnormal grain growth occurs, nano grains cannot be achieved; (II) if without traditional sintering additives, serious degradation of Si3N4 occurs, Si3N4 and SiC composite cannot be formed. Therefore, Al contained polymer-derived ceramics route opens a promising avenue to fabricate Si3N4/SiC nano-composites with fine grain size, uniform microstructure and excellent oxidation/corrosion resistance.