Role of molten pool shape and in-situ nano (Nb,Ti)C precipitation on mechanical properties in laser directed energy deposited IN718/TiC_p composite

The microstructure and mechanical properties of laser directed energy deposited TiC strengthened IN718 composite were investigated by mixing IN718 and 1 wt%TiC powders. It is confirmed that the nano (Nb,Ti)C phase is uniformly in-situ precipitated during laser directed energy deposition process, with an average size of 56.85 nm and an aspect ratio of 4.12. The microstructure exhibits a weaker grain texture and 36 % reduction in grain size, compared to that of the pure IN718. Specifically, the Laves phase presents a block-like distribution with an average size of 1.29 μm within the inter-dendritic regions, contrasting with the chain-like distribution observed in pure IN718, which has an average size of 3.1 μm. The weaker texture observed in the IN718/TiC_p composite can be attributed to changes in the molten pool shape. And the incorporation of TiC promotes HAGBs proportion within the composite by enhancing the trend of columnar-to-equiaxed transition. The IN718/TiC_p composite exhibits an increase of 32.2 % in yield strength and an increase of 16.8 % in ultimate tensile strength compared to the IN718 deposit. These improvements are primarily attributed to the dispersion strengthening and solution strengthening induced by in-situ precipitation of the nano (Nb,Ti)C phase.