FABRICATION OF NOVEL ALUMINA COMPOSITES REINFORCED BY SiC NANO-PARTICLES AND MULTI-WALLED CARBON NANOTUBES

摘要

A novel microstructure design of three phase alumina composites reinforced by nanosize SiC particles and multiwalled carbon nanotubes (MWNTs) is proposed. Alumina composites reinforced by different MWNTs contents ranging from 5, 7 and 10 vol% along with concurrent reinforcement of low volume fractions of SiC nanoparticles ranging from 1, 2 and 3 vol% were fabricated by spark plasma sintering technique based on proposed microstructure design. The nanocomposites have shown significant improvements in fracture toughness and bending strength, while hardness remains almost stable. The enhancement in fracture toughness was observed by change in fracture mode of alumina from intergranular to transgranular due to presence of SiC nanosize particles at the intragranular positions and further improvement has also been observed due to presence of MWNTs at intergranular positions making intertwining network structure around alumina grains in the matrix. The overall improvements in mechanical properties were ascribed to the complementary effect of MWNTs and SiC in strengthening and toughening of alumina matrix. The three hallmarks of toughening mechanisms in ceramic fiber composites i.e. crack deflection at the MWNTs/matrix interface, crack bridging by MWNTs at the grain boundaries and MWNTs pullout at the fracture surface were observed at the nano scale in the composites.