Preparation and high temperature oxidation behavior of refractory disilicide coatings for γ-TiAl intermetallic compounds

Novel refractory disilicide layers were applied to gamma-TiAl to enhance oxidation resistance at 1050 degrees C. NbSi2 and MoSi2 layers were prepared by joining thin Nb and Mo foils to gamma-TiAl surfaces, and siliconizing the combinations (Nb/gamma-TiAl, and Mo/gamma-TiAl) using molten salts. The coatings and their oxidation behavior were characterized using X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy techniques. Isothermal oxidation tests showed that the oxidation resistance of uncoated gamma-TiAl at 1050 degrees C in air was insufficient, and scale spallation occurred. NbSi2 coatings were formed and adhered firmly to the gamma-TiAI substrate, whereas Mo film detached from the substrate surface causing failure of the MoSi2 coatings. Oxidation of the NbSi2-coated gamma-TiAl (NbSi2/Nb/gamma-TiAl) at 1050 degrees C in air showed improved oxidation resistance at exposure times up to 100 h. Microstructural and compositional developments of the coatin, at prolonged time were discussed. The NbSi2 coatings provided sufficient oxidation resistance for gamma-TiAl at 1050 C in air, and have potential use in high temperature applications. (C) 2007 Elsevier Ltd. All rights reserved.