Direct Laser-Deposited IN718 Alloy: Effect of Heat Treatment Route on Microstructural Evolution and Mechanical Properties

The laser-based additive manufacturing techniques are widely used for the refurbishment of worn-out components. The post-processing treatments on additive manufactured parts will improve the material properties and meet the functional requirements. In this study, the multilayered deposition of Inconel 718, a nickel-based alloy is performed using fiber-coupled diode laser with 4 kW maximum output and 5.5 mm spot diameter of direct laser deposition technique. The fabricated samples were subjected to two different stages of heat treatment namely (i) solution-treated and (ii) solution-treated plus direct aged, aiming to study both stages of microstructural and mechanical properties of the deposit. Microstructural observations are carried out using SEM with EDS and microhardness measurements through Vickers indentation method. Further, the influence of different stages of heat treatment on microstructure formation is investigated individually for all multilayered samples. The heat treatment results show that, at different stages, the morphology and hardness differ irrespective of the number of layers. In addition, solution treatment with direct aging reveals precipitation of γ′ (Ni3Ti) and γ′′ (Ni3Nb) phases in the Ni-γ matrix. Further, a 40 to 50% increment in microhardness was obtained and the two-stage heat treatment process has given better results.