Microstructure and Properties of Nb/Nb5Si3 Composites Strengthened with Multiwalled Carbon Nanotubes by SPS

Abstract

Multiwalled carbon nanotubes (MWCNTs) were modified noncovalently with cetyltrimethylammonium bromide. The Nb/Nb5Si3 in situ composite material that was strengthened with MWCNTs was prepared by SPS. The effect of MWCNT content on the microstructure and properties of Nb/Nb5Si3 in situ composites was investigated. The results showed that the composites consisted of Nb, α-Nb5Si3 and β-Nb5Si3 phases. With the addition of over 2 wt% MWCNT, a new Nb4C3 phase was formed in the composites. The properties of the Nb/Nb5Si3 in situ composites were affected by MWCNT addition. The relative density, Vickers hardness and fracture toughness increased with increasing MWCNT addition. When the MWCNT addition was 2 wt%, the relative density and Vickers hardness reached a maximum and increased by ~ 1.4% and ~ 18%, respectively (relative to 0 wt% MWCNT addition). When the MWCNT content exceeded 2 wt%, the relative density and the Vickers hardness decreased. However, the fracture toughness of the Nb/Nb5Si3 composites with 3 wt% MWCNTs reached a maximum (an increase of ~ 68% relative to 0 wt% MWCNT addition). Scanning electron micrographs of the fractography showed brittle cleavage and partial intercrystalline composite fracture. The composite toughening mechanisms arose mainly because of MWCNT removal and bridging.