Modifications of an electrolytic aluminum oxide film under the treatment with microdischarges during plasma electrolytic oxidation, a self-organized dielectric barrier discharge (DBD) and a DBD-like plasma jet

Surface modifications of aluminium and aluminium oxide induced by a treatment with a He-plasma jet and plasma electrolytic oxidation

“…Figure 4 shows SEM images and EDS spectra of an analogous prepared aluminium substrate after a 5 min treatment with the He-plasma jet. Current-voltage characteristics of the treatment are very similar to those presented in [14] and are not presented here. During the treatment the distance between the nozzle of the plasma jet and the substrate surface amounts to 2 cm.…”

“…To better visualize the plasma interaction with the treated surface an additional gold layer is deposited before a plasma treatment based on results presented in [14,16]. Similar to [16], a gold layer with a thickness of 100 nm on the surface of a pretreated aluminium substrate stops the erosion process completely.…”

“…In a previous study [14], an amorphous aluminium oxide film was deposited on an aluminium substrate by a high voltage anodisation process and afterwards treated with microdischarges during high voltage PEO and with microdischarges at atmospheric pressure, namely a self-organized DBD (dielectric barrier discharge) and a DBD-like plasma jet operated with He/N 2 (95%/5%) gas flow. Despite strong differences in measured discharge characteristics the observed erosion trace characteristics, especially dimension, form and material distribution, left by all three microdischarges on the aluminium oxide surface were very similar and hence, a similar formation mechanism was assumed.…”

“…Despite strong differences in measured discharge characteristics the observed erosion trace characteristics, especially dimension, form and material distribution, left by all three microdischarges on the aluminium oxide surface were very similar and hence, a similar formation mechanism was assumed. Based on results of previous studies [14][15][16][17][18][19], the formation of plasma spots with a core and with a helical electric current and toroidal heating of the treated surface, was supposed. The following general conclusions of those studies were drawn: (a) a relatively cold plasma with a diameter of several hundred micrometers can be contracted to a plasma spot core with a diameter of about one micrometre, (b) the treated material can be destructed and partially extracted without melting and vaporisation, (c) plasmoids can be produced in the afterglow phase of plasma spots [19].…”

“…To figure out their ignition process and microdischarge nature, it is helpful to understand, how microdischarges can penetrate through slits and defects in dielectric coatings and if PEO microdischarges interact in a comparable way with certain surfaces like other atmospheric pressure plasma sources. Therefore, aluminium substrates and aluminium substrates pretreated with an anodisation procedure are treated with a DBD-like He-plasma jet and PEO process based on the first results presented in [14]. At that, gas flow swirls, a formation of artificial hot spots using substrate surface scratching, and an anodising pretreatment are used for the instigation of material erosion and possibly oxidation by the considered He-plasma jet.…”