Manufacture and characterisation of in situ titanium carbide reinforced Ti6Al4V composites by selective laser melting

Metal matrix composites (MMCs) offer various advantages over metallic alloys due to their low density, high strength, and tailorable properties. However, their manufacture with conventional methods is challenging due to the presence of hard particles. Selective laser melting (SLM) is a promising method for manufacturing MMCs, but the preparation of homogeneous powder feedstocks is a challenge for its widespread adaptation. This study examines the manufacture and characterisation of in situ TiC reinforced Ti6Al4V matrix composites using carbon-coated near-spherical Ti6Al4V powder feedstock via SLM. Spherical homogeneously coated carbon-Ti6Al4V composite powders were prepared by direct mixing to retain the flowability of particles. In situ TiC-Ti6Al4V composites were manufactured using this powder feedstock. TiCTi6Al4V composites' microstructure was examined using optical microscopy, X-ray diffraction, X-ray computed tomography, scanning electron microscopy, and electron backscatter diffraction. Microhardness tests, dry reciprocating wear tests and in situ SEM scratch tests were employed to assess the performance of Ti6Al4V-TiC composites. Nearly fully dense parts with homogeneously distributed TiC nanoparticles smaller than 500 nm size was achieved with optimum processing parameters. Lower SLM energy density led to lack of fusion defects, while high energy density resulted in keyhole pores. TiC presence induced parent ß grain and martensite lath refinement. Grain boundary length increased more than twice with TiC particle formation, and martensite lath size was reduced ~ 30%. The hardness of TiC-Ti6Al4V composites was measured as ~100 HV higher than their unreinforced equivalents. The wear rate of Ti6Al4V-TiC composites was measured as higher than unreinforced Ti6Al4V parts. In situ SEM scratch tests were showed that TiC particles may come off from the Ti6Al4V matrix under frictional forces, and third body abrasion may cause the higher wear rate. This study showed that nearly fully dense in situ TiC-Ti6Al4V composites can be manufactured using directly mixed composite powder feedstock.