Abstract
Aluminium oxide ceramic composite coatings containing hexagonal BN (h-BN) powder were produced successfully by a two-step microarc oxidation process. The incorporation of h-BN powder was achieved by means of wiping an emulsion into the pretreated coatings between these two steps. The thermal shock resistance of the fabricated samples was tested via quenching method. The morphological characteristics and the distribution of elements were analysed by SEM, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The microhardness of samples was determined by employing a Vickers indenter. The phase composition of composite ceramic coatings was investigated by X-ray diffraction. The results showed that the inclusion of h-BN powder has no influence on the growth and microhardness of alumina ceramic coatings. However, the modified coatings exhibit lower area and number of pores than conventional coatings. More significantly, the incorporation of a certain amount of h-BN powder improves the thermal shock resistance of aluminium oxide ceramic composite coatings even in a thick coating.
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