Abstract
The feasibility of using a high-entropy rare-earth oxide (REO) as a top coating material for thermal barrier coatings was explored using the atmospheric plasma spray technique. The microstructure and Vickers hardness of the coating layer were compared to those of an 8 mol % yttria-stabilized zirconia (8YSZ) top coating material. Macroscopic observations revealed the formation of a well-coated surface with no surface defects or delamination. Scanning electron microscopy images showed the presence of several parallel and vertical microcracks in the REO and 8YSZ coating layers. The origin of these cracks is attributed to differences in the coefficient of thermal expansion, very fast cooling, and process parameters. X-ray diffraction demonstrated the high phase stability and excellent thermal properties of REO due to the absence of phase transformation after plasma spray processing. The measured Vickers hardness of REO was 425 HV, which is lower than that of sintered REO powder and the 8YSZ coating.
Highlights
Thermal barrier coatings (TBCs), which are protective ceramic coatings applied to the surfaces of hot metallic sections, are widely used in gas turbines and aircraft engines, among others
The Co–Ni–Cr–Al–Y (Amdry 365-2) and rare-earth oxide (REO) powders were plasma sprayed onto the surface of a metallic substrate
SEM analysis demonstrated that REO could be coated without delamination or surface defects, similar to 8 mol % yttriastabilized zirconia (8YSZ)
Summary
Thermal barrier coatings (TBCs), which are protective ceramic coatings applied to the surfaces of hot metallic sections, are widely used in gas turbines and aircraft engines, among others. New research studies have revealed that formation of a single-phase solid solution in high-entropy materials is an effective method for enhancing the thermal properties of TBCs [28,29]. Recent studies have demonstrated that forming a high-entropy solid solution is an effective method for improving the thermal insulation properties of thermal barrier materials [16,32,33]. With the advancement of TBCs over recent decades, various methods have been developed to synthesize new TBCs with more promising properties and applications These methods are broadly divided into several categories, including the use of lasers, thermal spraying, vapor deposition, powder metallurgy, and chemical-based methods [35,36]. Research on applying high-entropy materials to the top coating of TBCs has recently been initiated.
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