Improved ductility of spark plasma sintered aluminium-carbon nanotube composite through the addition of titanium carbide microparticles

The prevalence of low fracture strain in metal matrix composites (MMCs), in comparison to the unreinforced matrix material, has always been a challenge, especially in CNT reinforced composites. The study investigates the improvement in the ductility of carbon nanotubes (CNT) reinforced aluminium matrix composite, through the introduction of 2.5 mu m titanium carbide (TiC) particles as a second reinforcement phase. The bimodal hybrid composite is fabricated by successive application of flake powder metallurgy of Al powder, solution coating of CNT on Al powder, spark plasma sintering, and hot extrusion of the resulting billet. Field-emission scanning electron microscopy (FE-SEM) analysis reveals that the solution coating process produced Al powder perfectly coated with individual CNTs. The pure Al so fabricated had a tensile strength of 125 MPa and elongation of 40%, while the tensile strength and elongation of the Al-0.5CNT composite of 232 MPa and 5.2%, respectively, is considered typical. However, introducing 2.5 wt% TiC microparticles to form Al-2.5TiC-0.5CNT hybrid composite, reduced the UTS to 186 MPa while the elongation increased to 33%. The role of dislocation generation and annihilation by the reinforcement phase is explored to explain the novel behaviour of the bimodal hybrid composite. The adverse effect of microparticles on the strength of the hybrid composite is contextualized in terms of strengthening mechanisms and a theoretical estimation.