Effect of silicon content on the corrosion behaviors of CrAlSiN thin films deposited by magnetron co-sputtering

One CrAlN and four CrAlSiN thin films containing 0.8-7.3 at. % Si were grown by a magnetron co-sputtering process using pure Cr, Al, and Si targets. The microstructure of the CrAlSiN coating changed from a coarse columnar structure to a dense and compact morphology as Si content increased from 0.8 to 7.3 at. % due to the formation of more amounts of amorphous silicon nitride phase to block the growth of columnar grains. Pitting corrosion was the main corrosion failure mechanism for each coating. According to the potentiodynamic polarization test, the lowest corrosion current density, the highest pitting potential, and the widest passivation range were obtained on the 7.3 at. % Si contained CrAlSiN coating. After the electrochemical impedance spectroscopy study of CrAlN and CrAlSiN thin films in 3.5 wt. % NaCl aqueous solution for 100 h immersion, the corrosion resistance of CrAlSiN thin films was 14 times higher than the CrAlN film due to its fine nanocolumnar microstructure to effectively retard the attack of corrosive electrolyte through the defects of coating.