In-situ fabrication of Ti-TiC<inf>x</inf> metal matrix composite by laser powder bed fusion with enhanced elastic modulus and superior ductility

The production of high stiffness Ti-based Metal Matrix Composites (Ti-MMCs) displaying significant ductility is extremely challenging due to the high reinforcement content required. This study outlines the production process of stiffness-driven Ti-TiC MMCs displaying a remarkable ductility. The process consists in powder Mechanical Blending, Laser Powder Bed Fusion (LPBF), and a heat treatment. A TiC fraction of more than 20 vol% was formed in-situ through the reaction of titanium with carbon during the LPBF process. The as-built sub-stoichiometric TiC dendrites are converted in equiaxed TiC grains during the heat treatment. The TiC C/Ti ratio was found to be close to 0.5 in as-built conditions, and 0.7 in heat treated conditions, resulting in an effective reinforcement content nearly twice the one expected for stoichiometric TiC, leading to stronger reinforcement. The mechanical analysis revealed a Young's modulus of up to 149 GPa and total elongations of up to 2.8 %. The former represents a 27 % improvement compared to commercially pure Titanium and the latter exceeds by 115 % reported values for LPBF Ti-MMCs with similar Young's modulus. It is enabled by the in-situ formation of defect-free TiC reinforcements during the LPBF process combined with their globularisation through heat treatment.