Abstract
The plasma spray process is used extensively in the aerospace industry for manufacturing key components exposed to excessively high temperatures, aggressive chemical environments, wear, abrasion, erosion and cavitation. The process covers a large field of parameters so that almost every layer can be combined with any other as well as with the base material. Coatings can be deposited uniformly; therefore, they allow worn components to be brought to final dimensions in the process of aircraft repair. This research shows an effective procedure of the application of plasma spray coatings on the parts of the Astazou IIIB turbo - jet engine in the process of repair. The engine manufacturer, Turbomeca, has prescribed that powders should be deposited by plasma spray systems under designation Metco 3M and 7M for the prescribed parameters of powder deposition, so that during the application of other plasma spray depositing systems the parameters must be tested and optimized. The aim was to apply the Plasmadyne plasma spray system during the repair process and to optimize the parameters, which will enable producing coatings that fulfill all the criteria prescribed in the engine manufacturer standard. The optimization of the parameters was carried out with a plasma gun MINI - GUN II with a large number of samples. This paper presents the optimal parameters of the deposition on the ASTAZOU III B engine casing, casing frame, duct and oil tank. The assessment of the coating mechanical properties was done by the HV0.3 microhardness testing method. Tensile bond strength of the coatings was investigated by a tensile test. The microstructures of the coating layers were evaluated on an optical microscope - OM. The analysis of the microstructures and the mechanical characteristics of the coatings was done in accordance with the TURBOMECA standard. The quality of the deposited coatings was confirmed by a 42-hour test of the ASTAZUOIIIB engine parts on a test stand. The performed tests have confirmed the quality of the coatings thus enabling the application of the plasma spray technology in the process of the ASTAZOUIIIB engine overhaul.
Highlights
The development of jet engines and the demands for increased resistance to oxidation, hot corrosion and sulphuring of engine parts influenced the development of the thermal spray process and nickelbased powders
This paper presents the optimum parameters with which coatings are deposited on turbine casing, casing frame, duct and oil tank as well as the mechanical and structural characteristics of the coatings tested on the Astazou III B turbojet engine on the test stand
There were no unfused powder particles of 45-60 μm, whose presence is allowed in a content of up to 15% by the Turbomeca standard (Turbojet engine-standard practices manuel, TURBOMECA)
Summary
The development of jet engines and the demands for increased resistance to oxidation, hot corrosion and sulphuring of engine parts influenced the development of the thermal spray process and nickelbased powders. The most effective protection of substrates from oxidation at temperatures above 800°C is provided by coatings which form oxides of the α-Al2O3 and Cr2O3 type. Coatings forming a continuous layer of α-Al2O3 are applied since this type of oxide is superior and more reliable as compared to other types of oxides (Mrdak, 2012, pp.182201). The diffusion processes are beginning to show their effects The nature of these effects depends on the content of the chemical elements in the coating and the diffusion parameters. NiO oxide is subjected to tensile stresses as a metal base, so that the elastic deformation of the metal substrate causes breakage and peeling of the oxide layer on the coating surface (Mrdak, 2012, pp.182201).
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