Fig.1 shows XRD patterns of reactive sprayed composite coatings as a function of different spray parameters. It is found that the reaction products are Fe, Al2O3, FeAl204 spinel, and a small amount of FeO wustite in four coatings. No pure Al or Fe2O3 phases can be detected, which implies that the reaction between Al and Fe2O3 has been completed. In addition, there seems to be more Fe phase in the coating S2.
Fig.1. XRD patterns of the composite coatings deposited by different spray parameters:(a)S1,(b)S2,(c)S3 and(d)S4.
Fig.2 displays the back scattering electron (BSE) images of cross-section morphologies of the coatings. The coatings show typical lamellar microstructure. They are extremely dense and almost imporous in comparison with monophase Al2O3 coatings deposited by normal plasma spray process. Unmelted or unreactive particles cannot be found in the coatings. Moreover, it is clearly observed that three different colored phases, namely white, grey and black, were formed during the reaction, and they are uniformly overlapped each other. Furthermore, in order to determine the element composition of these phases, the coating S2(Fig.2(b)) was used to act EDS analysis due to its more homogeneous microstructure. The EDS patterns are shown in Fig.4. Combined with XRD results of the composite coatings, the white phase corresponding to zone A can be assigned to a Fe-rich phase(Fig.3(a)); the grey zone B should be dedicated to a FeAl2O4-rich phase(Fig.3(b)), and the black zone C is highly rich in Al2O3 phase(Fig.3(c)). Thus, it can be concluded that the microstructure of the composite coatings built of three phases with different morphologies according to the observation of BSE images. The grey FeAl2O4-rich phase as the main framework possesses lamellar splat microstructure. The small ball-like Fe-rich metal particles are dispersed into the whole frame-work, meanwhile, the smaller black splats of Al2O3-rich phase were embedded into the FeAl2O4-rich phase matrix.
Fig.2. Cross-sectional morphologies of the composite coatings deposited by different spray parameters:(a)S1,(b)S2,(c)S3 and(d)S4.
Fig.3. EDS patterns corresponding to three zones of composite coating S2:(a) zone A.(b) zone Band(c) zone C.
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