In situ toughened SiC ceramics with Al-B-C additions and oxide-coated SiC platelet/SiC composites.

摘要

This work aimed at fabrication and characterization of high toughness SiC ceramics through the applications of in situ toughening and SiC platelet reinforcement. The processing-microstructure-property relations of hot pressed SiC with Al, B, and C additions (designated as ABC-SiC) were investigated. Through a liquid phase sintering mechanism, dense SiC was obtained by hot pressing at a temperature as low as 1700;The mechanical properties of the toughened SiC and the composites were evaluated in comparison with a commercial Hexoloy SiC under identical test conditions. The R-curve behavior was examined using the strength-indentation load relationship and compared with that directly measured using precracked compact tension specimens. The in situ toughened ABC-SiC exhibited much improved flaw tolerance and significantly rising R-curve behavior. A steady-state toughness in excess of 9 MPam;Higher fracture toughness was also achieved by the reinforcement of SiC platelets, encapsulated with alumina, yttria, or silica, in a SiC matrix. The coating prevented sintering reaction between the platelets and the matrix, enhanced densification of the composites, and more importantly provided a weak interface which promoted crack deflection and platelet pullout. The composite with alumina-coated platelets in a fine-grained matrix showed higher toughness than the corresponding monolithic material. Coupled toughening from coated-platelet reinforcement and matrix grain bridging resulted in a toughness of 8 MPam