The use of high entropy alloys with different compositions in thermal barrier coating systems and investigation of their high-temperature behavior

Thermal barrier coatings (TBCs) are complex systems that are especially used in high-temperature applications in the aerospace sector to provide thermal insulation and boost turbine efficiency. In general, TBC systems consist of a metal bond coated on a superalloy material and a ceramic top coating layer. In ceramic-based TBC systems used as top coatings, there are several elements that cause damage at high temperatures and restrict the system's lifetime. The main reasons for these disadvantages are thermal generalization inconsistencies between layers, changes in the thermal conductivity ratio, thermal shock effects and additional tensions resulting from sudden temperature changes, damage to the crystal cage structure following the change of the structure of the cage, high-temperature oxidation, hot corrosion effect, sintering effect, and erosive wear damage. With the advancement of today's technology, materials that are used in areas such as aircraft engine parts operating at high temperatures, hot components of aircraft, turbine wings/wings, space, aviation, and nuclear industries have increased the need for materials that provide thermal insulation, longer part life, fuel savings, high phase stability, and energy efficiency. These exceptional fundamental qualities have caused the emergence and rapid development of high-entropy alloys (HEAs) as an alternative coating material. As part of the thesis, metal bonding coatings, including CoNiCrAlY, were generated using the high-speed oxy-acetylated fuel coating (HVOF) technique on the Inconel 718 super alloy sub-material. Metal powders of varied compositions are combined using the mechanical alloying (MA) process and are generated as top-coating powders with HEA properties. HEA powders, generated in different compositions, are sprayed onto metal bond coatings using atmospheric plasma spray coating (APS) technology and have two different HEA contents (AlCoCrFeNiTi and AlCoCrFeNiZr). Manufactured in varied compositions, TBC systems have been submitted to isothermal oxidation tests for 5, 25, 50, and 100 hours at temperatures of 1000°C, 1100°C, and 1200°C, respectively, equal to those under service circumstances in the aviation industry. The heat corrosion tests of TBC systems were conducted at 700°C, 800°C, and 900°C for 1, 3, 5, and 10 hours. The findings of the isothermal oxidation and hot corrosion experiments have been examined and studied in depth. The differences acquired by analyzing the development of thermal-growing oxide (TGO) structure and growth behaviors have been recognized and described, taking into account studies in the literature. Micro-structural and mechanical parameters of TBC systems before and after manufacture and after high-temperature tests were determined and compared with stereo microscopes, SEM (scanning electron microscope), EDX-elemental mapping, porosity analysis, XRD (x-ray diffraction), and hardness tests. The findings have been compared in depth with current studies in the literature.