Studies On Compositions, Structure And Properties Of Fe-Al Intermetallics Prepared By Electroplating Al From Ionic Liquid At The Substrate Of 304 Foils

Aluminide coatings, which can form compact surface oxidation layers, are widely used in aeronautics & astronautics, nuclear reactors, fire-powered stations, petrochemical equipments because of their excellent anti-oxidation and anti-sulfide properties. Fe-Al intermetallics coating, one of the most representatives among them, also has its unique property like tritium resistant property despite its excellent anti-oxidation property. Traditional methods of the preparation of Fe-Al alloy coating like packed aluminisation and hot-dip plating aluminisation are conducted at high temperature, which will make detrimental harm to the mechanical properties of the substrate materials.Though there are some methods of Fe-Al alloy coating preparation at low temperature like low-temperature aluminisation and low-temperature hot-dip plating aluminisation, the prepared coatings are composed of several Fe-Al phases which can’t be easily discerned by X-ray diffraction. Therefore, the key point is how to prepare the single-phase Fe-Al intermetallics and analyzing the prepared phases with the help of more accurately TEM method. In this thesis, Fe-Al intermetallics are prepared at the substrate of 304 foils.Three kinds of Fe/Al thickness ratio specified samples were prepared through 304 foils electrodepositing Al from AICl3-EMIC (molar ratio 2:1) ionic liquid which correspond to three kinds of phase region specified Fe-Al alloys followed by low-temperature heat treatment. The metallurgical features and phase structures of these single-phased Fe-Al intermetallics under different Fe/Al thickness ratios were studied by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), through electron microscope (TEM) and X-ray diffraction (XRD). Results show that the obtained Fe-Al intermetallics are composed of FeAl phase. FeAl2+Al2Fe phase. Fe2Al5 phase respectively. During the analyzing process, the solid-soluted alloy elements do some effect on the lattice structures of Fe-Al intermetallics. And it is concluded as follows:the lattice structures of gained Fe-Al intermetallics are distorted which can be seen in the displacement of diffraction peaks at the XRD analysis and the difference of appearances under the SEM observation due to the existence of alloy elements like Cr. Ni. Mn.Also the mechanical properties and oxidation behaviors of prepared Fe-AI alloys were studied. The mechanical properties were measured through Vickers hardness tester. Results showed that the hardness of Fe-Al alloys were increased when the content of Al increased, while the toughness of correspond Fe-Al alloys acted conversely. While the oxidation properties of the three single-phased Fe-Al alloys were identified by oxidation test, surface oxides state inspection and anti-oxidation evaluation. The corresponding heat treatments were conducted at 740℃for 100 h under the air condition. The oxidization-products on the surfaces of Fe-Al alloys were studied by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), while the surface elements states were analyzed by characteristic X-ray diffraction. It turned out that a thin Al2O3 film formed at the surfaces of the three Fe-Al alloys after long time oxidation under the air. The existence of this thin film can effectively prevent substrates from further oxidation. Also the result showed that the thickness of these films increased when the Al content increased which means the anti-oxidation property of Fe2Al5 phase is the best among them.