Study by optical emission spectroscopy of a physical vapour deposition process for the synthesis of complex AlCuFe(B) coatings

Abstract

abstract Article history:Received 18 May 2010Accepted in revised form 18 May 2010Available online 23 May 2010Keywords:PVDQuasicrystalOptical emission spectroscopy We investigate the formation of complex Al Cu metallic phases by magnetron dc sputtering of elementaltargets followed by low temperature annealing. We show that all stable low temperature phases of the Al Cusystem can be grown this way and suggest that some of these phases could be used as an interfacial layer toimprove the adhesion of quasicrystalline AlCuFe coatings on metal substrate. Then we introduce opticalemission spectroscopy as a tool to monitor the composition of thin lms obtained by sputtering Al 63 Cu 25 Fe 12 and Al 59.5 Cu 25.3 Fe 12.2 B 3 targets. This method should improve the synthesis of complex metallic alloy phasesas new coating materials of industrial interest.© 2010 Elsevier B.V. All rights reserved. 1. IntroductionQuasicrystals are solids with long-range order but no translationperiodicity, exhibiting non-crystallographic rotational axis like ve-fold or tenfold symmetries[1]. They usually form in relatively narrowregions of binary or ternary phase diagrams. Their structural andchemical complexity is frequently associated with unique physicalproperties not encountered in simple metallic systems. Following thediscovery of quasicrystals by Shechtman et al., there has been anintense renewal of interest for binary Al-transition metal(s) systemscontaining complex metallic alloys (CMA) with very large unit cellsand exhibiting local cluster features similar to those found inquasicrystalline phases[2 10]. It was found that both quasicrystalsand CMA possess speci c properties like low friction, poor wettingand good corrosion resistance which are of interest to develop newcoating materials[11 14]. Those surface properties are related totheir peculiar electronic structure characterized by a low density of Al3p states at the Fermi level, usually associated with a poor metallicbehavior. In particular, experiments show that their surface energy isrelatively low compared to normal metallic systems which makes thedeposition of CMA and quasicrystals on metallic substrates verychallenging[14,15].Strategies can be developed to circumvent the poor adhesion ofthese alloys on metallic substrates for example by using an interfaciallayer such as to obtain a gradient of properties between the substrateand the surface[16].Resortingto PVD processes to deposit both the buffer layer and thequasicrystal is a technologically reliable method as already describedby several groups[17 20]. A crucial point in such PVD processes is thecontrol of the chemical composition of the deposit, due to the limitedcompositional ranges of quasicrystalline and CMA phases. In thisarticle, we present a study of the synthesis of new coatings containingCMAphasesintheAl Cusystembyreactivediffusioninthesolidstatebetween bilayers deposited by dc magnetron sputtering. The aim is todevelop an interfacial layer to improve the adhesion between aquasicrystalline Al Cu Fe thin lm and a metal substrate. Then, wedescribe some rst results on the possibility to follow the compositionof thin lms in the Al Cu Fe system by optical emission spectroscopy.This possibility is particularly interesting to check any drift with timein the deposition process.2. Experimental detailsThe Al/Cu and Al/Cu/Fe multilayers can be grown by dc magnetronsputtering using the experimental set-up shown inFig. 1. The basepressure in the sputtering system is 1.10