Microstructure and high-temperature oxidation resistance of iridium coating electrodeposited from chloride-based molten salts
[Introduction]With the rapid advancement of aerospace technology,the performance requirements for the hot-end components of aircraft are becoming increasingly stringent.Iridium(Ir),known for its exceptional melting point,excellent corrosion resistance,and high strength,along with stable physicochemical properties,is considered as the ideal protective coating material for hot-end components.[Method]Iridium coating was prepared on high-purity rhenium substrate by electrodeposition in NaCl-KCl-CsCl-IrCl3 molten salts.The suitable temperature range for electroplating was firstly determined through thermogravimetric analysis.The effects of temperature and cathodic current density on the surface morphology and elemental composition of Ir coating were studied by scanning electron microscopy(SEM)and energy-dispersive spectroscopy(EDS).The phase structure of Ir coating obtained under the optimized conditions was analyzed by X-ray diffraction(XRD),and its resistance to high-temperature oxidation was tested by high-temperature ablation.[Result]The NaCl-KCl-CsCl-IrCl3 molten salts began to melt at 490℃and volatilize at 596 ℃.The volatilization rate of the molten salts was increased with the increasing of temperature,and up to 0.5%/min at a temperature of 650℃.The suitable electrodeposition temperature was from 550℃to 650℃.The Ir coating electrodeposited at temperature 600℃and cathodic current density 0.2 A/cm2 was continuous,compact,highly pure,and featured a face-centered cubic polycrystalline structure with preferred orientation of(111)and good resistance to high-temperature oxidation.[Conclusion]A continuous,compact,and pure Ir coating can be prepared by adjusting the electrodeposition parameters of chloride-based molten salts,and its resistance to high-temperature oxidation can be further improved.
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