Strengthening and toughening effects of MWCNTs on Si2BC3N ceramics sintered by SPS technique

MWCNTs modified Si2BC3N ceramics were prepared through SPS sintering mechanically alloyed amorphous Si2BC3N powder and MWCNTs at 1900 °C in N2 atmosphere. The phase evolutions, microstructures and mechanical properties of the prepared ceramic were characterized by XRD, SEM and TEM (SAED and HRTEM), as well as the properties testing. The results show that the Si2BC3N ceramics are mainly composed of β-SiC, α-SiC and BN(C) phases. The introduction of MWCNTs can stimulate the formation of β-SiC in comparison with the pure Si2BC3N ceramics. Meanwhile, the particle sizes of BN(C) and SiC are reduced with the introduction of MWCNTs. Furthermore, the MWCNTs are mainly embedded in the Si2BC3N matrixes, contributing to enhanced bonding. Judging from the interfacial characteristic, the strengthening and toughening mechanisms of MWCNTs in Si2BC3N ceramics can be classified as “crack bridging”, “pull-out” and “crack deflection”. Based on these effects, the 1 vol% MWCNTs incorporated Si2BC3N ceramics have much higher flexural strength and fracture toughness of 462.1 MPa and 5.54 MPa·m1/2, respectively.