Study on Solidification Microstructure and Mechanical Properties of Inconel 718 Alloy Fabricated by CMT MIX+Synchropulse Direct Energy Deposition-Arc

Thin-walled Inconel 718 components are fabricated using CMT MIX+Synchropulse (CSP) as the heat source, and the solidification microstructure transformation under multi-layer and multi-pass thermal history and its relationship with the mechanical properties are investigated. The results indicate that the solidification microstructure of CSP-DED-Arc Inconel 718 alloy primarily consists of γ+TiN+(Nb,Ti)C+NbC +Laves. Significant morphological variations in the Laves phase are observed across different regions of the sample. At the bottom of the thin-walled sample, where the cooling rate is high, the Laves phase predominantly exhibits granular or short rod-like morphology. In the middle and upper regions, characterized by slower cooling rates and a prolonged high-temperature exposure, the Laves phase mainly assumes a long chain-like morphology, with sufficient time for the precipitation of γ″. At the top region, despite a slow cooling rate, the absence of subsequent thermal cycling inhibits the γ″ precipitation, resulting in a blocky Laves phase morphology. Influenced by the morphology of the Laves phase and the precipitation behavior of γ″, both the microhardness and tensile strength along the build direction of the thin-walled alloy initially increase and then decrease with the number of deposited layers. The values in the middle region are the highest, those in the bottom region follow and those in the top region are the lowest. The elongation after fracture follows the opposite trend. The tensile strength in the wall axis direction is lower than that in the build direction direction, while the elongation after fracture is higher than that in the build direction direction.