Improvement of Mechanical Properties of Natural Mullite/SiC Nanocomposites

Abstract

The natural aullite (fabricated from natural kaolin and Al₂O₃ powders)/SiC nanocomposites were prepared by pressureless reaction-sintering at 1700'C. These composites were composed of mullite with columnartyped grains, fine SiC dispersions and amorphous grain boundary phases. The larger SiC particles (>0.3μm) were dispersed at the grain boundaries, while the finer SiC particles (<0.2 μm) were located not only at the grain boundaries but also within the mullite matrix grains. The microstructure of these composites could be controlled by changing SiC dispersions, heating rate and sintering time. The mechanical properties were strongly improved. The Vickers hardness, fracture toughness and fracture strength were 10 GPa, 2.7 MPam^1/2 and 490 MPa, respectively, which are comparable with those of highly pure mullite and their composites. In this paper, special emphasis was placed on the understanding of effects of SiC dispersions and sintering conditions on mechanical properties.