Microstructure evolution and high-temperature strength retention of SiC ceramics densified using Pr3Si2C2-xOx sintering additive

Pr 3 Si 2 C 2-x O x was employed as a sintering additive to enable low-temperature densification of SiC ceramics. Dense SiC ceramics were obtained through hot pressing at 1550 °C under 20 MPa. During sintering, Pr 3 Si 2 C 2-x O x undergoes oxygen-assisted phase transformation, decomposing into SiC and crystalline Pr-O compounds that form stable solid-solid interfaces at grain boundaries. Microstructural analysis using TEM, HRTEM, and EDS confirmed the formation of these crystalline intergranular phases, while EELS demonstrated partial oxygen substitution in the Pr 3 Si 2 C 2 lattice. Mechanical testing under an Ar atmosphere revealed that the sample with Pr:Si atomic ratio of 1:7 retained a flexural strength of 313 MPa at 1400 °C, corresponding to 95% of its room-temperature strength. Compared with conventional liquid-phase-sintered SiC, the crystalline grain-boundary phases significantly suppress intergranular softening at elevated temperatures. This work establishes a clear link between additive-induced microstructural evolution and high-temperature mechanical stability, providing a promising strategy for the low-temperature fabrication of high-performance SiC ceramics.