Induction effect of α-Al2O3 seeds on formation of alumina coatings prepared by double glow plasma technique

(FeAl/Al) + alpha-Al2O3 coatings were deposited directly onto the 316 L stainless steel substrate and then oxidized at a temperature as low as 580 degrees C using double glow plasma technique. The complex Al target containing 10 wt.% alpha-Al2O3 seeds was used in the experiment. The microstructure, chemical composition and phase components of the sputter-deposited and oxidized coatings were characterized respectively by glancing-angle X-ray diffraction (GAXRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), field emission transmission electron microscopy (FETEM) and high-resolution transmission electron microscopy (HRTEM). The results indicated that the coatings were very dense and uniform. Cross-sectional FETEM observation indicated the thickness of the film was about 5.83 mu m, by which the deposition rate was calculated as high as similar to 1.46 mu m/h. The surface of the coatings was composed of pure alpha-Al2O3 while the inner layer of the coatings was mostly alpha-Al2O3 with little gamma-Al2O3. These intriguing results were attributed to the dual effects of both the alpha-Al2O3 seeds and the high-energy ion bombardment, which provided more nuclei for the growth of alpha-Al2O3 and more energetic species at the surface of the coatings respectively. Furthermore, the coatings were well-bonded to the substrates because a SS/FeAl/(Al2O3 + Fe2O3)/Al2O3 structure was formed at the interface so as to improve the coefficients of thermal expansion mismatch between the substrate and the deposited coatings. (C) 2013 Elsevier B.V. All rights reserved.