Abstract
The paper presents the comparison of the structures of the zirconium modified aluminide coatings deposited on pure nickel by the CVD and PVD methods. In the CVD process, zirconium was deposited from the ZrCl3 gas phase at the 1000°C. Zirconium thin layer (1 or 7 μm thick) and aluminum thin layer (1.0, 0.7 or 0.5 μm thick) were deposited by the EB-PVD method. Deposition velocity was about 1 ?m/min. The layers obtained by the Electron Beam Evaporation method were subjected to diffusion treatment for 2 h in the argon atmosphere. The obtained coatings were examined by the use of an optical microscope (microstructure and coating thickness) a scanning electron microscope (chemical composition on the cross-section of the modified aluminide coating) and XRD phase analysis. Microstructures and phase compositions of coatings obtained by different methods differ significantly. NiAl(Zr), Ni3Al and Ni(Al) phases were found in the CVD aluminide coatings, whereas Ni5Zr, Ni7Zr2 and γNi(Al,Zr) were observed in coatings obtained by the PVD method. The results indicate that the microstructure of the coating is strongly influenced by the method of manufacturing.
Highlights
The improvement of engine turbines efficiency is achieved by the use of effective cooling systems of turbine blades and by diffusion protective coatings on nickel-based superalloys [1,2,3]
The microstructures of zirconium doped aluminide coatings deposited for 2 and 5 hours by the chemical vapor deposition (CVD) method at 1020 ̊C are presented in Figures 3 and 4, and the chemical compositions on the cross sections are shown in Tables 1 and 2
The microstructure of the coatings obtained in the CVD and electron beam physical vapor deposition (EB-PVD) processes were examined by the use of Nikon Epiphot 300 optical microscope, a scanning Hitachi S-3400N scanning electron microscope (SEM) and an energy dispersive spectroscope (EDS)
Summary
The improvement of engine turbines efficiency is achieved by the use of effective cooling systems of turbine blades and by diffusion protective coatings on nickel-based superalloys [1,2,3]. It is the aluminum oxide layer that limits the amount of oxygen that can diffuse into critical engine components causing a catastrophic failure. TBCs are used to protect superalloy engine components from the harsh environments that they are exposed to as a result of operation in gas turbine engines. Temperature in these engines can exceed 1650 ̊C and metal temperature can reach 1200 ̊C. Bond coats are designed to form an external protective α-Al2O3 scale during high temperature operation. Adhesion of this thermally-grown scale is necessary to maintain the ceramic top coat. Any spallation of the alumina scale results in loss of the overlying ceramic coating
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