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

ABSTRACT 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.