Abstract
The effects of exposure to overheating (temperature above 1000 °C) on the degradation (modification) of layers of coatings (coatings based on aluminum) of uncooled polycrystalline rotor blades of aircraft turbine jet engines were investigated under laboratory conditions. In order to determine the nature of the changes as well as the structural changes in the various zones, a multi-factor analysis of the layers of the coating, including the observation of the surface of the blades, using, among others, electron microscopy, structural tests, surface morphology, and chemical composition testing, was carried out. As a result of the possibility of strengthening the physical foundations of the non-destructive testing of blades, the undertaken research mainly focused on the characteristics of the changes occurring in the outermost layers of the coatings. The obtained results indicate the structural degradation of the coatings, particularly the unfavorable changes, become visible after heating to 1050 °C. The main, strongly interacting, negative phenomena include pore formation, external diffusion of Fe and Cr to the surface, and the formation and subsequent thickening of Fe-Cr particles on the surface of the alumina layer.
Highlights
Aircraft engine turbine rotor blades are exposed to very demanding in-service conditions such as, among others, varying mechanical aerodynamic/thermal loads and the generally high-temperature of exhaust gases
The basic requirement for an aluminide layer is connected with high temperature oxidation and the protection of turbine blades against hot corrosion
Acting as a protective coating, the layer is exposed to high temperatures, which may cause its structural degradation/modification
Summary
Aircraft engine turbine rotor blades are exposed to very demanding in-service conditions such as, among others, varying mechanical aerodynamic/thermal loads and the generally high-temperature of exhaust gases. There is a strong tendency to improve the performance of aircraft engines by increasing the temperature of its exhaust gases. Aluminum diffusion coatings can be produced using, among others, the pack cementation, the out of pack, the slurry processes, or the chemical vapor deposition methods [6,7,8,9,10]. Aluminum coating utilizing CVD (Chemical Vapour Deposition), one of the most up to date techniques, allows for the covering of complex-shaped elements, both internal and external, thanks to which it has found use in coating turbine blades with cooling channels [3,4,5,11]
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