Electrochemical behaviour of chromium nitride coatings with various preferred orientations deposited on steel by unbalanced magnetron sputtering

Abstract

Chromium nitride coatings Cr₂N(111) and preferred orientations of CrN(111) and CrN(200) were successfully deposited on AISI 304 stainless steel by an unbalanced magnetron sputtering method. The electrochemical corrosion properties of the deposited films were studied in a 0·5M H₂SO₄ + 1M NaCl aqueous solution at ambient temperature by electrochemical measurements, including the corrosion potential E_corr, linear polarisation, potentiodynamic polarisation and electrochemical impedance spectroscopy. The structural characterisation and surface morphology were investigated using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The experimental results indicated that the CrN(200) coating possesses the best corrosion resistance property, followed by the CrN(111) coating, while the Cr₂N coating has the least resistance among the three types of CrN(111), CrN(200) and Cr₂N(111) coatings. The porosity, corresponding to the ratio of the polarisation resistance of the uncoated and the coated substrates, was higher in the Cr₂N(111) coating than in the other CrN coatings. The CrN(200) coating had a dense microstructure almost without porosity. The void defects of CrN(111) and Cr₂N(111) coatings are responsible for the decrease in corrosion protection.