Microstructure and mechanical properties of TiC/Ti6Al4V nanocomposites fabricated by gas-liquid reaction laser powder bed fusion

Herein, we report a novel method for in-situ synthesis of nanometer-scaled TiC-reinforced Ti6Al4V-matrix composites (TMCs) via laser powder bed fusion (LPBF). The formation mechanism can be summarized as insitu additive manufacturing (AM) via a gas-liquid reaction. Here, gas means the laser-induced pyrolysis methane gas (CH4) generates gaseous carbon (C) atoms/ions and liquid means that the laser beam irradiates Ti6Al4V powder to create a Ti matrix melt pool. TiC, which is the reaction product of gaseous C atom/ion with liquid Ti atom, initially undergoes nucleation and growth, and subsequently precipitates from the Ti matrix melt pool during fast LPBF cooling process. Finally, the TiC-reinforced TMCs are fabricated via a layer-wise gas-liquid reaction. With this method, three nanocomposites (Sample 2, 3 and 7) fabricated in low CH4 concentration (9 vol % and 19 vol%) exhibited good dispersion, clean interface and strong interfacial bonding between the TiC reinforcement and Ti matrix. Thus, it achieved a good combination of simultaneously high strength and high plasticity. The effects of CH4 concentration, laser power and scanning speed on the microstructures and mechanical properties including microhardness, compression behaviors and wear resistance were systematically studied. And the strengthening and toughening mechanisms of the TMCs were elucidated. The proposed in-situ AM method via the gas-liquid reaction would carve a new path for manufacturing uniformly dispersed nanophase reinforced composites with excellent mechanical properties and complex geometries.