Formation of the gradient metal matrix Ti-TiB-TiC composite by 3D-printing with coaxial electron-beam technology and cored wire

A metal matrix composite (MMC) based on titanium matrix reinforced with TiB and TiC particles was obtained by 3D printing by electron beam melting and cored wire as feedstock material. The wire was made of a mixture of fine Ti and B₄C powders wrapped into titanium foil. MMC was formed due to the in-situ reaction between Ti and B₄C, the component ratio was selected to achieve 40 % (vol.) of reinforcing TiC +TiB phases in the titanium matrix. MMC layers were deposited on the surface of the base Ti-6Al-4V plate. During 3D printing, a gradient in the composition and microstructure state of the MMC was formed. The bottom layer adjacent to the Ti-6Al-4V substrate has a relatively low concentration of TiC and TiB particles (not more than 30 vol%) while approaching the surface, the concentration of hardening particles increases to almost 90 %. This gradient microstructure ensures a smooth change in hardness by more than 2 times along the height of the MMC layer. Thermodynamic calculations and a model experiment on the in-situ interaction between Ti and boron carbide have shown the possibility of implementing various reaction mechanisms between them depending on the ratio of the initial materials and the reaction temperature. The microstructure of 3D printed MMC are compared with the results of calculations and a model experiment.