Effects of nitrogen gas ratio on the structural and corrosion properties of ZrN thin films grown on biodegradable magnesium alloy by ion-beam sputtering

Studies on the corrosion resistance of magnesium alloys, which are widely applied as biomaterials, have increased in recent years. In this work, zirconium nitride (ZrN) coatings were deposited on AZ91 magnesium alloy through ion-beam sputtering at 473 K with 0.3, 0.4, 0.5, and 0.6 nitrogen proportions [F(N-2)] in ionized gas. X-ray diffraction, profilometry, hardness tests, scanning electron microscopy, and potentiodynamic polarization techniques were used to analyze the structure, thickness, adhesion, microstructure, and corrosion resistance of coated samples, respectively. Results showed that the (111) crystalline orientation dominated in all coatings. Williamson-Hall technique revealed that the crystallite size of ZrN films decreased from 73 to 20 nm with increasing F(N-2), and compressive microstrain increased from 0.004 to 0.030. Film thicknesses were inversely correlated with N-2 amount and significantly decreased from 1.7 to 0.8 mu m. The maximum dP/dr ratio, a dependent factor of adhesion, was 0.04 kg/cm for the film deposited under the F(N-2) value of 0.5. The corrosion potential of coated samples was not significantly different from that of uncoated AZ91. Under the F(N-2) value of 0.6, corrosion current density slightly decreased from 14 to 9.7 mu A/cm(2) and significantly increased to 13.5 mu A/cm(2). Results indicated that ZrN film deposited under the F(N-2) value of 0.5 showed high adhesion and corrosion resistance.