Effect of carbon nanotubes on the microstructure and tribological properties of in situ synthesized MWCNTs/Ti6Al4V composites fabricated by Selective laser melting

• TiCx/Ti6Al4V composites have been in situ manufactured by SLM. • The effect of MWCNTs on surface quality and microstructure evolution is studied. • Fine lamellar substoichiometric TiCx is formed through an in-situ reaction. • The formation mechanism of substoichiometric TiCx nanoparticles is revealed. Multi-walled carbon nanotubes (MWCNTs)/Ti6Al4V composites have been in situ manufactured by selective laser melting (SLM) of 1 wt.% MWCNTs modified Ti6Al4V composite powder. The effect of MWCNTs and volume energy density on microstructure evolution and wear properties of the SLM-fabricated Ti6Al4V alloys is investigated. The addition of MWCNTs has an insignificant influence on the surface quality, but changes the epitaxial growth of β grains in molten pool. Fine lamellar substoichiometric TiCx is formed via an in-situ reaction. High hardness of 471 ± 12 HV 0.2 is obtained for the MWCNTs/Ti6Al4V composites, increasing by ∼ 30% compared to that of the Ti6Al4V alloy. The MWCNTs/Ti6Al4V composites exhibit high coefficient of friction (COF) and a low wear rate due to favorable bonding of TiCx/matrix and in-situ synthesis of nanoscaled hard TiCx.