Investigation of oxidation and hot corrosion behavior of coatings with manganese slag content

Slag, a waste product of metal production, is the residue or residual material, mostly oxides, that forms on the surface during the smelting of processed metal ore. This slag is treated as a by-product of metal production and is often used in recycling processes. In general, slag recycling is both environmentally and economically important. Recovering waste slag reduces raw material consumption, saves energy and reduces environmental impact. Therefore, the effective management and recycling of slag in the metal industry is of great importance. Slag is an alternative candidate for use in high temperature application areas, considering its mechanical properties, the valuable elements it contains and environmental pollution due to its significant amount of release in the industry. In addition, slag material provides advantages such as high temperature resistance, thermal insulation, lightness, durability and strength. Thanks to these properties, slag materials have started to be used as top coating material in the production of thermal barrier coatings used to increase productivity and performance in many industrial sectors, especially in the aerospace industry. In this study, metallic based bond coatings with CoNiCrAlY content were produced on nickel based Inconel 718 super alloy materials with a diameter of 25.4 mm and a thickness of 5 mm using high velocity oxy fuel (HVOF) technique. Thermal barrier coatings (TBC) system was obtained by using atmospheric plasma spray (APS) coating method of manganese slag with oxide content produced during manganese production on metallic based CoNiCrAlY bond coatings. The produced TBC systems were subjected to isothermal oxidation tests at 600°C for 5, 25, 50 and 100 hours. X-ray diffractometer (XRD) analyses, scanning electron microscopy (SEM) analyses, energy dispersive spectrometer elemental mapping (EDS) analyses, porosity and hardness measurements were performed to determine the formation of damage mechanisms, structural and microstructural change processes before and after oxidation and hot corrosion tests of TBC systems. Compared to the metallic and ceramic coating materials used in conventional TBC systems, the use of Manganese slag in the upper ceramic coating structure has enabled the use of a waste product material in a surface engineering method such as thermal spray coating. The oxidation and hot corrosion damage formation processes of the TBC system successfully produced using Manganese slag were evaluated. It has been observed that the TBC system with Manganese slag content maintains its strength without structural degradation at the specified temperature and time processes and can be used in alternative industrial applications.