High‐Temperature Structural and Dielectric Stability of Hot‐Pressed SiC sf /Y ₂ Si ₂ O ₇ Composites in Vacuum and Argon

High‐temperature stability of structural–functional ceramic composites is essential for their application in extreme environments. In this work, short silicon carbide fiber‐reinforced yttrium disilicate (SiC sf /Y 2 Si 2 O 7 ) composites with a relative density of ∼95% were fabricated by hot pressing, and their structural and dielectric stability was evaluated after heat treatment at 1000°C in vacuum and argon atmospheres. The composites exhibited excellent stability under both nonoxidizing conditions. After argon treatment, more than 95% of the flexural strength, flexural modulus, and fracture toughness was retained, indicating strong intrinsic structural stability. Under vacuum, representing a low‐pressure nonoxidizing environment, the composites retained over 85% of their initial flexural strength and 97% of their fracture toughness. Meanwhile, effective K u ‐band microwave attenuation was maintained, with minimum reflection losses of −17.12 dB and −12.43 dB after argon and vacuum treatments, respectively. XRD, XPS, and TEM analyses confirmed the phase stability of the β‐Y 2 Si 2 O 7 matrix and the preservation of fiber–matrix interfaces after high‐temperature exposure. The retained dielectric response was mainly attributed to the stable microstructure, interfacial polarization, and conduction loss associated with SiC sf . These results demonstrate that SiC sf /Y 2 Si 2 O 7 composites are promising structural–functional ceramic materials for high‐temperature low‐oxygen environments.