Tailoring Laves phase and mechanical properties of directed energy deposited Inconel 718 thin-wall via a gradient laser power method

Directed energy deposition (DED) of Inconel 718 is a promising process for the reconstruction of aerospace components, but a large number of Laves phases precipitated in inter-dendrites can impair the mechanical properties of the reconstructed parts. This paper puts forward a gradient laser power (GLP) deposition method to tailor the morphology and content of the Laves phase effectively, thereby enhancing the mechanical properties. The deposited Inconel 718 parts with the same volume as the Inconel 718 substrate were fabricated by different laser powers to simulate the practical thin-wall repair. An infrared camera was utilized to capture the thermal information during the DED process. The thermal-history-dependent microstructure, residual stress, microhardness and tensile properties were comprehensively investigated. The results indicate that the GLP method not only alleviates heat accumulation but also increases cooling rates and lateral heat dissipation. For GLP samples, the discrete and fine Laves phases tailored with a uniform distribution are featured by fine columnar dendrites with random growth direction, in sharp contrast to their long-chain interconnected configurations obtained by the conventional constant laser power (CLP) deposition method. Compared with CLP samples, GLP samples show compressive residual stress, high hardness and excellent ductility of elongation 30.09 % with comparable strength.