Advanced Graded Protective Coatings, Deposited by EB-PVD

Abstract

Electron beam technology (EB-PVD) and equipment for one-stage deposition of advanced graded protective coatings using a composite ceramic ingot for evaporation are described. This technology allows replacing the flat interface between coating layers by a graded transition zones and achieve of a high degree of reproducibility of the composition, structure and lifetime of the functionally graded coating in compare with traditional multi-stages technologies of protective coating deposition.A design of the composite ceramic ingot is considered, as well as the ability to regulate in a broad range the composition, structure and properties of all levels of the graded protective coating including transition zones and coating layers. Examples and variants of advanced graded protective coatings with their structures and properties are given (thermal barrier, hard erosion-resistant and damping coatings) for aerospace and gas-turbine industry application deposited by one-stage EB-PVD process. Total cost of one-stage EB-PVD deposition process at least 2 times less in compare with traditional technological processes of protective coating deposition due to using only one EB-PVD unit and elimination of multistage nature of process cycle.Laboratory and productive electron-beam units designed and manufactured at ICEBT are considered. Development of modern protective coatings, technologies and equipment for their application is focused, primarily, on improvement of the durability and main service properties of the coating/protected item system, ensuring a reliable reproducibility of the coating structure and properties, shortening the cost and time of the entire technological cycle of their deposition. The existing traditional technologies of deposition of multilayer protective coatings, for instance, thermal barrier coatings (TBC), containing a oxidation-resistant metal bond coat and outer low thermal-conducting ceramic layer, are multi-stage, with combination of such processes as diffusion saturation, galvanic coating, plasma spraying and electron beam deposition [1-3]. Use of diverse expensive equipment, availability of intermediate mechanical and thermal treatments, as well as the operations of surface cleaning, apply considerable limitations both on widening of the sphere of such coating application, and their further development in terms of improvement of the structure and properties. The one-stage electron beam technology developed at ICEBT for deposition of advanced protective coatings based on evaporation of a composite ingot and allowing deposition of functionally graded coatings in one process cycle, meets the above goals to a considerable extent [4,5]. The technology is based on the use of the known phenomenon of fractionating at evaporation of multicomponent systems, containing elements with different melting temperature and vapour pressure, and their subsequent condensation under vacuum, allowing the flat interface, for instance between the metal and ceramic layers, to be replaced by a transition zone of the graded composition and structure. Fig.1 gives the schematic and appearance of a composite ingot used for one-stage deposition of advanced graded protective coatings in vacuum by its electron beam evaporation from one crucible. The ingot base material determines the purpose of the graded coating. For instance, Al2O3, TiC, TiB2, B4C, MgO, etc. can be used as the base of the ingot for deposition of hard wear-resistant, erosion-resistant and damping coatings. For the case of TBC, this is zirconium dioxide with additives