Fabrication, microstructure, and properties of SiC/Al4SiC4 multiphase ceramics via an in-situ formed liquid phase sintering

The SiC/Al4SiC4 composites with the improved mechanical properties and thermal conductivity were fabricated by the in-situ reaction of polycarbosilane (PCS) and Al powders using spark plasma sintering. The addition of 5 wt% yttrium (Y) sintering additive was useful to obtain fully dense samples after sintering at a relatively low temperature of 1650 degrees C, due to the formation of a liquid phase during sintering. The average particle size of the in-situ formed SiC was ~300 nm. The fracture toughness (4.9 MP center dot m(1/2)), Vickers hardness (16.3 GPa), and thermal conductivity (15.8 W/(m center dot K)) of the SiC/Al4SiC4 composite sintered at 1650 degrees C were significantly higher than the hardness (13.2 GPa), fracture toughness (2.16 MPa center dot m(1/2)), and thermal conductivity (7.8 W/(m center dot K)) of the monolithic Al4SiC4 ceramics. The improved mechanical and thermal properties of the composites were attributed to the high density, fine grain size, as well as the optimized grain boundary structure of the SiC/Al4SiC4 composites.