Papers by Keyword: Electron Beam Deposition

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Authors: Naoki Oyanagi, Shin Ichi Nishizawa, Kazuo Arai
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Authors: Boris A. Movchan, Kostyantyn Yu. Yakovchuk
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
1681
Authors: Marcia S. Domack, Karen M. Taminger, Matthew Begley
Abstract: The electron beam freeform fabrication (EBF3) layer-additive manufacturing process has been developed to directly fabricate complex geometry components. EBF3 introduces metal wire into a molten pool created on the surface of a substrate by a focused electron beam. Part geometry is achieved by translating the substrate with respect to the beam to build the part one layer at a time. Tensile properties have been demonstrated for electron beam deposited aluminum and titanium alloys that are comparable to wrought products, although the microstructures of the deposits exhibit features more typical of cast material. Understanding the metallurgical mechanisms controlling mechanical properties is essential to maximizing application of the EBF3 process. In the current study, mechanical properties and resulting microstructures were examined for aluminum alloy 2219 fabricated over a range of EBF3 process variables. Material performance was evaluated based on tensile properties and results were compared with properties of Al 2219 wrought products. Unique microstructures were observed within the deposited layers and at interlayer boundaries, which varied within the deposit height due to microstructural evolution associated with the complex thermal history experienced during subsequent layer deposition. Microstructures exhibited irregularly shaped grains, typically with interior dendritic structures, which were described based on overall grain size, morphology, distribution, and dendrite spacing, and were correlated with deposition parameters. Fracture features were compared with microstructural elements to define fracture paths and aid in definition of basic processingmicrostructure- property correlations.
1291
Authors: F. Danie Auret, A.G.M. Das, C. Nyamhere, M. Hayes, N.G. van der Berg
Abstract: In this study we have investigated the thermal stability (in the range 100 oC - 900 oC) of defects introduced in p-Si by electron beam deposition (EBD) of Ti and Ti/Mo Schottky contacts. The depletion regions below these contacts were probed by conventional deep level transient spectroscopy (DLTS) as well as Laplace (high-resolution) DLTS (L-DLTS). We have chosen Ti as the Schottky contact because the barrier height of Ti/p-Si (0.53 eV) is close to that of TiSi2/p-Si (0.50 eV) that forms after annealing at 600 – 650 oC. The Mo was added on top of the Ti in order to prevent annealing degradation. These contacts were annealed in Ar at temperatures of up to 900 oC in 100 oC steps for half-hour periods. Current – voltage (I-V) and capacitance – voltage (C-V) measurements were used to monitor the quality of the Schottky contacts. DLTS was performed after each annealing cycle to monitor the presence of the EBD-induced defects and to obtain heir electronic properties. We have found that that the Ti/Mo contacts were superior to the Ti contacts. Their (Ti/Mo) barrier height after EBD was 0.52 eV and it gradually increased to 0.56 eV after annealing at 500 oC - 600oC and then dropped to 0.50 eV annealing at 700 oC. DLTS revealed that the main defects introduced during metallization are hole traps H(0.17), H(0.23), H(0.37) and H(0.49). Annealing at 350 oC introduced an additional hole trap H(0.39). After annealing at 550 oC all defects were removed from the depletion region.
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