High-Temperature Mechanical Property Improvements of SiC Ceramics by NITE Process

Abstract

Dense SiC ceramics fabricated by NITE process (NITE-SiC), using SiC nano-powder, were subjected to exposure tests from 1000 to 1800 � C in an argon-oxygen gas mixture with an oxygen partial pressure of 0.1 Pa. The thermal stability of NITE-SiC was examined through mass change, 3-point bending test, XRD analysis and TEM/SEM observation. The NITE-SiC presented excellent bending strength (above 800 MPa) up to � 1800 � C while the conventional liquid-phase sintered SiC ceramics (LPS-SiC), using SiC sub-micron powder, indicated severe degradation at 1300 � C due to volatilization and softening of amorphous grain boundary phase. The in situ 3-point bending test at 1300 � C was carried out to evaluate in-service fracture behavior, where excellent improvements in bending strength, elastic modulus and fracture behavior were confirmed, compared with the conventional LPS-SiC. These are interpreted by the modification with reduction and crystallization of grain boundary phase (Y3Al5O12). The decomposition of Y3Al5O12 were caused by the reactions with CO gas on the surface of NITE-SiC exposed at 1800 � C, but the severe degradation was not identified in strength.