Novel performance in physical and corrosion resistance HfN/VN coating system
By Escobar, C.; Villarreal, M.; Caicedo, J.C.; Aperador, W. & Prieto, P.
Published in Surface and Coatings Technology
2013
Abstract
4140 steel substrates were coated with hafnium nitride/vanadium nitride multilayered with the objective of improving their corrosion resistance. The multilayered coatings were grown via a reactive r.f. magnetron sputtering technique by systematically varying the bilayer period (Λ) and the bilayer number (n) while maintaining constant the total coating thickness (~ 1.2 μm). The coatings were characterized by X-ray diffraction (XRD), electron and transmission microscopy. The electrochemical properties were studied by Electrochemical Impedance Spectroscopy and Tafel curves. XRD results showed preferential growth in the face-centered cubic (111) crystal structure for [HfN/VN]n multilayered coatings. The best enhancement of the mechanical behavior was obtained when the bilayer period (Λ) 15 nm (n = 80) which yielded the highest hardness (37 GPa) and elastic modulus (351 GPa). The values for the hardness and elastic modulus are: 1.48 and 1.32 times greater than the coating with n = 1, respectively. The maximum corrosion resistance was obtained for coatings with (Λ) equal to 15 nm, corresponding to bilayer n = 80. Polarization resistance and corrosion rate was around 112.19 kΩ cm2 and 0.094 ∗ 10- 3 mmy respectively, these values were 172.6 and 0.007 times better than those shown by the uncoated 4140 steel substrate (0.65 kΩ cm2 and 0.014 mmy, respectively).