Tailored microstructure and enhanced high temperature behavior of TiC/ Inconel 718 composites through dual-gradient printing strategy in direct energy deposition

The mismatch between the content of ceramics and laser power can lead to defects such as pores, microcracks, and grain coarsening, which resulted in the contradiction between tensile strength, ductility, and hightemperature behavior of TiC/superalloy composites. In this study, control methods for the microstructure evolution of TiC/Inconel 718 composites were investigated through dual-gradient printing strategy in direct energy deposition. Results indicated that this strategy, which involved a gradual increase in laser power and TiC addition amount in direct energy deposition processing, facilitated the transformation of Inconel 718-5 wt%TiC dual-gradient materials from columnar crystals to equiaxed crystals and the formation of carbides. This strategy effectively increased the number of heterogeneous nucleation points and solidification rate, while reducing temperature gradients, thereby forming a gradient-evolved microstructure. A significant amount of intragranular and intergranular carbides of the dual-gradient materials has enhanced stability of grains and grain boundaries at both room temperature and high temperature. Meanwhile, the internal fine equiaxed grains and carbides of Inconel 718-5 wt%TiC dual-gradient materials provided greater toughness. Inconel 718-5 wt%TiC dual-gradient materials exhibits a room temperature tensile strength of 859 MPa and an elongation of 18.2 %, along with a high temperature tensile strength of 746 MPa and a unit area oxidation weight gain of 0.5 mg/cm2. The dualgradient printing strategy has addressed the contradiction between high tensile strength, low ductility, and high-temperature performance of TiC/Inconel 718 composites.