Fluoride-doped MWCNT/Si3N4 composite with improved mechanical and structural properties

Abstract

The addition of carbon nanotubes (CNT) in ceramic composites has stimulated a substantial interest due to their high mechanical, thermal and electrical properties. This approach used fluoride additives (AlF3 and MgF2) to prepare multi-walled carbon nanotubes/silicon nitride (MWCNT/Si3N4) composite densified at 1700 °C for 1 h by hot press (HP) sintering. The microstructural analyses of MWCNT/Si3N4 composites indicate that the fluoride additives have substantially improved densification and the transformation of α-Si3N4 to β-Si3N4. As observed, the mechanical properties, i.e. flexural strength, fracture toughness, Young's modulus and hardness of MWCNT/Si3N4 composites are improved with an increasing concentration of MWCNT. These results attributed to the highly dense composites, strong interfacial interaction and the pull-out mechanism of MWCNT and β-Si3N4. The maximum values of fracture toughness flexural strength, Young's modulus, and hardness were 12.76 ± 1.15 MPa.m0.5, 883 ±46 MPa, 260 ±9 GPa, and 26.4 ± 1.3 GPa, respectively. The improved mechanical properties also ascribed to the synergistic strengthening and toughening influence of MWCNT and β-Si3N4.