Densification and Degradation Mechanisms of NITE-SiCf/SiC Composites Using Pr3Si2C2 Additive

A novel Pr 3 Si 2 C 2 additive was introduced to lower the sintering temperature of NITE-SiC f /SiC composites to 1550°C–1650°C. Pr 3 Si 2 C 2 effectively promoted densification, achieving 3.11 g/cm 3 density and 4.9% open porosity at 1600°C. However, the densification process causes severe thermochemical damage to the interphase layers and fibers. At 1550°C–1600°C, a kinetically-dominated “transient Pr-rich layer” is formed at the fiber/interphase boundary. This stems from a three-order-of-magnitude disparity in Pr-ion diffusion coefficients between the BN interphase and SiC fiber (At 1550°C, D BN ≈ 9.66 × 10 −13 m 2 /s vs. D SiC ≈ 8.31 × 10 −16 m 2 /s). Above 1650°C, Pr 3 Si 2 C 2 decomposition products react with the BN to form SiC, Pr 25 B 14 C 26 , and Pr 6 O 11 , shifting interfacial bonding from weak (23 MPa) to strong (154 MPa). Concomitantly, the Pr-bearing liquid phase infiltrates fibers along grain boundaries, inducing abnormal grain growth (from 8.8 to 54 nm) via Ostwald ripening. This caused monofilament tensile strength to drop from 2771.5 to 624.6 MPa and the Weibull modulus from 6.11 to 3.65. Combined interfacial degradation and fiber lead to a decline in composite performance, with the fracture mode shifting from pseudoplastic to brittle. This study elucidates the corrosion mechanisms of Pr 3 Si 2 C 2 on SiC fibers and BN interphases, providing a crucial theoretical foundation for optimizing the processing window of NITE-SiC f /SiC composites.