Mechanical properties of AlN thin films deposited on Al 5083 substrates by magnetron sputtering under different bias voltages

Mechanical properties of AlN thin films deposited on Al 5083 substrates by magnetron sputtering under different bias voltages

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  Mechanical properties ofAlN thin films deposited on Al 5083 substrates by magnetron sputtering under different bias voltages M. Piccoli1, J. García Molleja2*, J. Bürgi3 1Department of Engineering, University of Rome ‘Roma Tre’, Via della Vasca Navale 79, 00146 Rome, Italy 2Yachay Tech University, School of Physical Sciences and Nanotechnology, 100119 Urcuquí, Ecuador 3Instituto de Física Rosario (Conicet-UNR), Bv. 27 de Febrero 210 bis, S2000EZP Rosario, Argentina MOTIVATION Aluminum nitride (AlN) is a ceramic compound with many interesting properties, like a high band gap, high sound speed and good resonator performance. This is the reason that AlN can be used in optics, electronics and telecommunication fields. Furthermore, AlN can act as protective coating on substrates with a poor wear resistance and low hardness. In this work thin AlN films were deposited on Al 5083 alloy substrates in order to investigate the AlN mechanical properties and its adhesion properties in order to protect the selected substrate. This aluminum alloy, in particular, was chosen because it is used in automotive industry, especially in high friction environments. EXPERIMENTAL AlN films were deposited by sputtering magnetron technique (75% N2 – 25% Ar) and different substrate bias conditions (self-bias, 60 V, 100 V and 150 V) in order to analyze the influence of this experimental parameter on adhesion properties. The morphology of the AlN coatings was obtained with SEM and SAED; film hardness and elastic modulus were calculated after microindentation tests; residual stress was determined using a new characterization technique called ‘FIB pillar’ [1] and film adhesion was obtained after scratch tests. *Corresponding author: [email protected] RESULTS The film microstructure and residual stresses are linked to the film hardness. Furthermore, high bias voltages develop a residual stress increase in films due to the increased peening effect of the incoming ions and a progressive deterioration of film adherence [2]. CONCLUSIONS Protective AlN films on Al 5083 alloys were deposited by magnetron sputtering under different bias conditions. Substrate bias promotes finer AlN grains in the columnar structure of the film, higher hardness and elastic modulus and a rise of film residual stress, confirmed by the FIB pillar technique. However, when high bias voltages are used, a threshold is detected where the film adhesive performance is reduced. ACKNOWLEDGMENTS Authors are indebted to Marco Sebastiani and Daniele de Felicis for the development of the FIB pillar technique. Authors thank the collaboration of Edoardo Bemporad and Jorge Feugeas. Also, Universitat de Barcelona (Spain) is acknowledged. REFERENCES [1] M. Sebastiani, G. Bolelli, L. Lusvarghi, P.P. Bandyopadhyay, E. Bemporad, Surface and Coatings Technology 23 (2012) 4872- 4880. [2] E. Chason, B.W. Sheldon, L.B. Freund, J.A. Floro, S.J. Hearne, Physical Review Letters 88 (2002) 156103. More bias develops more residual stress, thus finer grains with higher hardness. Film adherence falls after a threshold.