Characterization of Al2O3 coatings oxidized from Al with different proportion of seed crystals at a lower temperature

Al layer with alpha-Al2O3 seed crystals was prepared on the surface of 316L stainless steel (SS) by a double cathodes discharge technique, in which the mixed targets of pure Al doped with different proportions of alpha-Al2O3 were used. Then, Al2O3 coatings were obtained after plasma oxidization at 580 degrees C. The phase composition, microstructure and morphology of the coatings were studied respectively by means of glancing-angle (1) X-ray diffractometry (GAXRD) and scanning electron microscopy (SEM). Furthermore, the bonding force and corrosion resistance of the coatings were measured. The results indicated that alpha-Al2O3 nucleated and grew surrounding the seed crystals as the Volmer-Weber Mode. The Al2O3 coating was compact, performing a good corrosion resistance and metallurgical bonding. The inducing effects of alpha-Al2O3 with different fractions were discussed. alpha-Al2O3 (5.5 wt.%) was distributed in the Al layer when the target possessing 10% alpha-Al2O3 was used. After plasma oxidation, 65.54 wt.% alpha-Al2O3 was obtained which was 10.34% more than that obtained by the oxidation of pure Al at the same condition. However, the inducing effects became weak with the further increment of content of alpha-Al2O3 seed crystals. (C) 2013 Elsevier B.V. All rights