Influence of TiC addition on the microstructures of TiC/IN718 composites fabricated by blue diode laser additive manufacturing

This study investigates the influence of TiC addition on defect formation, microstructural evolution, and microhardness in Inconel 718 (IN718) metal matrix composites (MMCs) manufactured using a blue-diode laser powder bed fusion (LPBF) system. Porosity and defects in the samples were analyzed using microscopes and an X-ray computed tomography system (X-ray CT). The microstructures of the baseline IN718 and MMCs were observed using microscopy and wavelength-dispersive spectrometry techniques. The microhardness measurements were conducted to confirm the effect of TiC addition and carbide precipitation. It was found that TiC addition had three main effects: (1) increased porosity from 0.02 to 0.07% at 200 mm/s scan speed and from 11.52 to 23.48% at 400 mm/s scan speed compared to the baseline IN718, (2) precipitated (Nb,Ti)C, and (3) enhanced grain refinement from an average grain size of greater than 9.44 to 8.80 µm at 200 mm/s and 5.07 µm at 400 mm/s scan speed. The partial remelting in the layer-by-layer process promotes TiC dissolution, enabling the formation of complex (Nb,Ti)C carbide precipitates. These precipitates subsequently serve as nucleation sites and form refined equiaxed grain structures. Higher microhardness values of 389.71 and 381.27 HV0.2 at 200 and 400 mm/s scan speeds, respectively, are important evidence of the improved mechanical properties through complex microstructural evolution. This study provides insights into the microstructural evolution of the MMC system fabricated by the blue diode LPBF process. It offers potential approaches for microstructural control in additively manufactured superalloy components for aerospace and energy applications.