Investigation of solid particle erosion wear behaviour of thermal barrier coatings at high temperature

In this study, High Temperature Solid Particle Erosion (HTSPE) wear behaviours of Thermal Barrier Coatings (TBC), which are applied for the purpose of increasing the strength and heat insulation on the materials having high temperature working conditions used in systems such as energy conversion plants, aerospace systems, jet engines and gas turbines, were examined. In the experiments, current and comprehensive parameters affecting erosion wear were investigated using variable operating temperatures at working conditions and different abrasive particle impact angles and constant impact velocity and abrasive particle size. In order to observe the comparative effects of erosion wear tests, studies on erosion resistance at room temperature (21°C) and high temperatures (300°C and 600°C) have been focused. Erosion tests were carried out in a specially designed HTSPE test ring in accordance with ASTM G211 internationally accepted standard test method. For this purpose, the air at the inlet of the compressor was heated and pressurized and then combined with abrasive particles and hit the test sample surface. Abrasive particle impact velocity was determined as ~ 97 m/s by widely used, simple, and cheap double disc method which stated in the literature. High strength super alloy Inconel 718 was selected as a substrate material and two different bond coatings (NiCrAlY and NiCoCrAlY) obtained by applying Atmospheric Plasma Spray (APS) method on the surface of this material and, ceramic top coating (ZrO2–8Y2O3) were applied separately on these two bond coatings in the experiments. Four different test specimens were obtained as a result of APS coatings. The hardness, surface roughness and porosity measurements were performed to determine the mechanical properties of the experimental groups. Student t test comparisons were performed to determine if the means of two sets of data are significantly different from each other. These samples were subjected to HTSPE tests with three different impact angles (30°, 60° and 90°), three different temperature values, under the effect of 400 µm alumina (Al2O3) abrasive particles and constant impact velocity. According to the experimental results, erosion rate graphs were formed according to temperature, angle, abrasive size and velocity effect and SEM images of surface deformations of test specimens were obtained and interpreted wear conditions. In addition, the elemental homogeneity conditions in the samples were proved by taking images from the surfaces of the test samples coated by APS method, with EDX and EDX mapping. As a result of the experiments, it was found that only bond coated specimens showed ductile material behaviour and maximum erosion wear occurred at 30° abrasive particle impact angle, while ceramic top coated samples showed brittle material behaviour and maximum erosion wear angle was at 90° abrasive particle impact angle. This showed that, when the erosion rate comparisons were made in the specimens due to the difference in impact angle, resistance to erosion wear tended to increase in the experiments at 600°C as a result of the thermal barrier efficiency. Cobalt (Co) only contributed positively to increase the erosion resistance in the bond coated specimens, while the erosion rate increased with the increased porosity of ceramic topcoats with cobalt added bond coating.