Evaluation of the properties of Inconel® 625 preforms manufactured using WAAM technology

Additive manufacturing is a constantly evolving technology that makes possible to manufacture highly complex parts by adding material layer by layer, as opposed to the various conventional manufacturing methods. Among additive manufacturing technologies, the Wire Arc Additive Manufacturing (WAAM) process stands out for its ability to manufacture large components with high mechanical properties and is a candidate to replace components manufactured by processes such as casting and forging. In order to increase the maturity of the process and understand the limits of the technology, this work objective is to evaluate the mechanical and metallurgical properties of a preform manufactured by the WAAM process on a substrate of the same alloy, comparing them with the reference material. To this end, the WAAM process was used to manufacture an Inconel® 625 preform, using wires as the deposition raw material and a substrate of the same alloy supplied forged. In order to select the processing window for the material, a Design of Experiment (DOE) was carried out, using deposition parameters as factors, such as: welding speed, stick-out, wire feed speed, shielding gas type and flow rate, among others, with the response of the experiment (DOE) being the geometric variables of the deposited layers (layer height and width) and the thermal input generated. After processing the information and selecting the processing window, four preforms were manufactured, following the same parameterization. After this, representative samples were taken to characterize the mechanical properties achieved and evaluate the metallurgical behaviour. Samples were prepared for macro and micrographic analysis through an optical microscope, a scanning electron microscope, mechanical hardness tests and tensile test specimens in three directions: vertical, horizontal and at the intersection with the substrate. After carrying out the mechanical tests on the preform and the substrate, the differences in mechanical properties were evaluated, with the sample manufactured by WAAM caracterizing lower strength and tensile limits than the forged Inconel® 625 substrate, however, with greater elongation when compared to the same forged material. The presence of solidification dendrites with porosity in the interdendritic regions and niobium microsegregation in the interdendritic regions were also observed. One hypothesis for the observations in this work is associated with anisotropy arising from the multiple thermal cycles that occur in the process, making it possible to obtain better properties after carrying out a heat treatment compatible with the microstructure of interest.