Improvement of the electrochemical behaviour of AlN films produced by reactive sputtering using various under-layers

Aluminium nitride films were deposited by reactive sputtering on steel subs trates (H 11) with the aim of realising anti-corrosion coatings. The porosi ty of the films combined with their inadequate thickness cause the good ini tial corrosion resistance of the samples to decrease drastically during imm ersion time in a 0.5 M NaCl solution. In order to create a corrosion barrie r between AlN and steel, three types of under-layers were investigated: nic kel under-layers (with a thickness of about 10 mum) deposited by both elect rochemical and electroless methods, and titanium under-layers (with a thick ness of about 1 mum) obtained by sputtering. The structure and morphology o f the samples were studied from X-ray diffraction (XRD), atomic force micro scopy (AFM) and scanning electron microscopy (SEM) observations. Electroche mical impedance spectroscopy (EIS) tests versus immersion time were carried out in a 0.5 M NaCl solution in order to compare their corrosion resistanc e. It appears that AlN/electroless nickel shows the best corrosion resistan ce, whereas the AlN/electrochemical nickel and AlN/titanium samples are alm ost in the same range. (C) 2001 Elsevier Science Ltd. All rights reserved.