Additive manufacturing (AM), the name itself describes the manufacturing process of building 3-dimensional (3D) objects by layer-upon-layer addition, where the production of the end product is technique and principle specific. A diverse set of processes are used to form feedstock (wire, sheets, and powders) to 3D geometries, where all the metal additive manufacturing parts undergo melting and bonds together into a dense component. Standard metal AM has four categories namely Powder Bed Fusion (PBF), Direct Energy Deposition (DED), Binder Jetting (BJ), Sheet Lamination (SL). The focus of work is mainly concentrated on the PBF category which has two subclasses i.e., Laser Melting Powder Bed Fusion (LM-PBF) and Electron Beam Powder Bed Fusion (EB-PBF)s. EB-PBF process gives a greater advantage over the other processes is that this process uses vacuum in its cell, protecting sensitive locations from contamination and likely entrapment of gas porosity originating from the process gas used in other laser-based processes. EB-PBF process utilizes a high-energy electron beam to melt metallic powders in layer by layer order to build the final parts. Alloy 718 is nickel-based superalloy and investigations based on sulfur-induced corrosion are not explored, as well as the oxidation performances are studied to establish a comparation between either of the cases. Industrially used Alloy 718 is selected for corrosion and erosion-corrosion investigations. Surface modifications techniques such as thermal spraying was explored by depositing NiCoCrAlY coatings using high velocity air-fuel process. Studies were also explored to understand the influence of post-processing such as combined hot isostatic pressing and heat treatment. This work investigates the influence of thermal spraying, i.e., HVAF-sprayed NiCoCrAlY coating and thermal post-treatment (i.e., HIP-HT) on sulfur-induced high-temperature corrosion and erosion-corrosion performances of EB-PBF-built Alloy 718. A continuous Cr-rich oxide scale was found on the uncoated samples exposed to ambient air, whereas a very thin Al-rich oxide scale was formed on the coated samples. With the salt, a discontinuous Nb-rich globular oxide scale was identified at distinct locations on all the coated and uncoated samples. The corrosion products on the coated and uncoated samples were significantly affected by the impingement of the erosive particles, which resulted in high-stress concentration zones and the formation of cracks in the underlying materials.