The structure and morphology of the surface of duplex layers after saturation of the base layer with carbon

Abstract

The paper presents a new method of obtaining aluminium-oxide-based, duplex-type layers. In the first stage, the base layer is produced via the hard anodising of aluminium alloys in order to obtain the optimal structural and morphological properties. Following anodising, the samples with an Al2O3 layer are rinsed in distilled water in order to remove the electrolyte. Graphite was introduced into the structure of aluminium oxide during a thermal treatment in a solid medium consisting of graphite dust. Afterwards, the properties of the obtained layers were determined using a scanning electron microscope, a transmission electron microscope and an atomic force microscope (AFM), as well as X-ray diffraction. The structure of the duplex-type layers contains carbon and other precipitates, which are typical for an alloy with additions of Fe, Mn, Cr and other elements. Carbon precipitates have a relatively weak connection with the matrix, as an envelope with numerous discontinuities forms around each carbon precipitate. Carbon precipitates are considerably larger than alloy precipitates, have micrometre dimensions, occur in groups and are composed of small grouped nanometric particles that form larger agglomerates. This means that there are nanometric particles inside the micrometric ones. Keywords: aluminium alloys, nano-layers, SEM, AFM, EDŜ lanek predstavlja novo metodo za izdelavo dupleksne plasti aluminijevega oksida. V prvi stopnji se izdela osnovna plast s trdim anodiziranjem aluminijevih zlitin, da se dobi optimalno strukturo in morfolo{ke lastnosti. Po anodizaciji so vzorci z Al2O3 plastjo potopljeni v destilirano vodo, da se izpere elektrolit. V strukturo aluminijevega oksida se uvede grafit med toplotno obdelavo v trdem mediju, ki je vseboval grafitni prah. Potem so bile dolo~ene lastnosti dobljenih plasti, s pomo~jo vrsti~nega elektronskega mikroskopa, presevnega mikroskopa in mikroskopa na atomsko silo (AFM), kot tudi z rentgensko difrakcijo. Struktura dupleksnih plasti je vsebovala izlo~ke ogljika in druge izlo~ke, ki so zna~ilni za zlitine, z dodatkom Fe, Mn, Cr in drugih elementov. Izlo~ki ogljika imajo relativno {ibko povezavo z osnovo, saj nastaja okrog vsakega izlo~ka ogljika ovojnica s {tevilnimi diskontinuitetami. Izlo~ki ogljika so mnogo ve~ji kot izlo~ki zlitin, imajo mikrometrske dimenzije, se pojavljajo v skupinah in so sestavljeni iz malih gru~nanometri~nih delcev, ki tvorijo ve~je skupke. To pomeni, da so znotraj mikrometrskih delcev prisotni nanometrski delci.

Effect of the base material condition on the structure and properties of Al2O3 oxide layers

“…In this connection, the knowledge of the mechanism of formation and growth of oxide layers obtained via the hard anodizing method is essential. Based on the outcomes of the research on obtaining oxide layers on aluminium in the first few seconds of electrodeposition, it can be affirmed that the initially active places are roughness peaks of the substrate metal's surface, as well as the places with crystal lattice deformations and other defects of the anode surface [1][2][3] .…”