Microstructure evolution and mechanical properties of high-content TiC reinforced Inconel 718 composites fabricated by laser-directed energy deposition

Abstract

Although increasing the content of ceramic reinforcement in metal matrix composites can improve some mechanical properties of processed parts, it brings significant challenges to forming technologies such as laser additive manufacturing. In this study, the high-content 60 wt. % TiC reinforced Inconel 718 composites were fabricated by laser-directed energy deposition (LDED). The influence of the laser energy density (E) on the forming quality, microstructure development, and mechanical properties of the high-content TiC/Inconel 718 composites was investigated. It revealed that a smooth and continuous TiC/Inconel 718 deposition layer was fabricated at a proper E of 144.44 J/mm2. It is identified by x-ray diffraction that the high-content TiC/Inconel 718 composites contained two phases of Ni-Cr-Fe and TiC, and the Ni-Cr-Fe phase is the matrix phase of Inconel 718 superalloy. During the LDED process, the TiC particles melt and then precipitate without any phase changes. With increasing laser energy input, the TiC grain morphologies gradually experienced successive changes from an irregular shape to significantly refined and smoothened as an octahedron shape, and then to further refined as a near-octahedral shape with the growing tips. The dispersion state of the TiC reinforcing particles was homogenized due to the efficient Marangoni convection within the molten pool. At the optimized E of 144.44 J/mm2, the high-content TiC/Inconel 718 composite showed a relatively high average microhardness of 495.08 HV0.5, a low average coefficient of friction of 0.65, and a wear rate of 0.72 × 10−4 mm3/(N m). This research provides a fundamental understanding of high-content ceramic reinforced nickel matrix composites by laser-directed energy deposition.