Experimental Research On The Preparation Technology Of High-temperature Oxidation Resistance Coatings On TiAl Alloy Surface

TiAl intermetallics alloys (TiAl alloy for short) are new type high temperature structural materials applied for aerospace and aircraft industries because of their low density, high strength and good creep resistance. The problem of poor ductility of these materials at room temperature has been mostly solved by alloying and microstructure controlling. Thus the problem of farther improving high-temperature oxidation resistance has become one of the most important research subjects. In this paper, high-temperature oxidation resistance of several coatings fabricated by different techniques on TiAl alloy was researched. The surface morphology, microstructure and phase of the coatings before and after oxidation were investigated using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). The oxidation mechanism of the different coatings was also disscused based on the oxidation kinetics, oxides morphology and microstructure, etc.(1). High-temperature oxidation behavior of double glow plasma surface chromized layers was studied. The results showed that a compact Cr2O3 oxide film was formed on the surface of the chromized layer after high-temperature oxidation. Although the oxide layer appeared local spalling phenomenon after a long-term oxidation, a new Cr2O3 layer can be reformed soon. Therefore, the chromized layer had a good high-temperature oxidation resistance.(2). High-temperature oxidation resistance of NiCoCrAl-Y2O3 coatings prepared by the technologies of the plasma spraying and plasma spraying-laser remelting was analyzed. The results showed that plasma-sprayed NiCoCrAl-Y2O3 coating had some defects, such as loose, porous and microcrack. The coating had a higher compactness, the lamellar structure of plasma-sparyed coating was eliminated and the bond state between the coating and substrate became metallurgical combination from mechanical combination after laser remelting. So the laser-remelted sample had better high- temperature oxidation resistance than the plasma-sprayed coating did.(3) High-temperature oxidation behavior of conventional and nanostructured thermal barrier coatings (TBCs) obtained by the techniques of the plasma spraying and plasma spraying-laser remelting was evaluated. The results showed that to the same material, the high temperature oxidation resistance of the laser-remelted TBCs was better than the plasma-sprayed TBCs'. To the same technologies, the high temperature oxidation resistance of the nanostructured TBCs was better than the conventional TBCs', but the improving effect was not significant.