Post-Processing of Inconel 718 Alloy Fabricated by Additive Manufacturing: Selective Laser Melting

The review analyses Inconel 718 (IN718) alloy, which is the nickel-based superalloy and has great application in industries due to its superior mechanical properties even at elevated temperatures by means of the solid-solution strengthening and precipitation strengthening. However, because of the tool over-wear, poor part surface integrity, high hardness and low thermal-conductivity properties, it is difficult to manufacture finished products with using conventional machining methods. It is especially urgent for the products of complex designs. In this regard, justification is given for the widespread use of modern additive manufacturing (AM) for the fabrication of the products from IN718. The most popular is AM based on the selective laser melting (SLM) technique, which can fabricate complex geometries with superior material properties. At the same time, the metal parts fabricated by SLM suffer from excessive residual porosity, residual tensile stress in the near-surface layer, and the formation of a relatively rough surface. In addition, the SLM-inherited surface defects can cause stress concentration to initiate cracks, reducing the fatigue strength of the printed parts. The review focuses on identifying potential solutions to the surface-finish complex additive manufactured to improve the surface properties to meet the industry requirements. Therefore, the improvement of the IN718-alloy-parts’ surface properties printed by the SLM becomes especially relevant. Currently, different surface post-processing technologies are being developed to obtain the expected surface quality of the SLM-components. As demonstrated, the finish surface enhancement treatments led to significant improvement in the wear resistance, corrosion resistance, increase in fatigue life, and tensile strength of the metallic materials. Therefore, adapting surface post-processing technologies has become a growing area of interest as an effective tool for improving the functionality and service lifetime of SLM IN718-alloy components. The review aims to analyse the main results of the most systematic studies of the currently developed surface post-treatments aimed to improving the surface-structure quality and properties of the IN718 parts fabricated by SLM. These results contribute to a better understanding of the role of the various-parameters’ effects on the surface improvements during the surface post-processing and changes in the structure–phase state, and physical, chemical and mechanical properties. Examples of the effects of a series of surface post-processing methods are presented: laser polishing, mechanical magnetic polishing, cutting finish-machining operations, shot peening, sandblasting technique, ultrasonic-impact treatment, and electrochemical polishing.