Properties and corrosion behaviour of reactive magnetron sputtered TiAlN coatings on AISI 316L SS in simulated bodily fluid

Because of their superior properties, titanium aluminium nitride (TiAlN) films are increasingly applied as protective layers on cutting and forming tools and turbine compressor blades and as biocompatible barriers. TiAlN films were deposited on AISI 316L stainless steel substrates by reactive magnetron sputtering using a target consisting of equal segments of titanium and aluminium. X-ray diffraction characterisation showed that the coating structure was face centred cubic. AFM and SEM studies indicated that the coatings are regular with dense shpherical granular structure. The coatings were also characterised using photoluminescence spectroscopy and Raman microscopy to elucidate the optical and acoustic phonon modes of the cubic lattices. Characteristic peaks were observed at 250, 620 and 1180 cm⁻¹ in laser Raman studies. Polarisation and impedance spectroscopy studies on TiAlN and TiN coated specimens were conducted in Fusuyama simulated body fluid. The charge transfer resistance R _ct increased in the order: uncoated 316L substrate; 2 μm TiN film; 3 μm TiN film; 2 μm TiAlN film. Thus, the TiAlN coating has the highest corrosion resistance, and was also found to have the most noble corrosion potential and lowest corrosion rate in the polarisation tests.