Anticorrosion behaviour and tribological properties of AZ31 magnesium alloy coated with Nb2O5/Nb2O5-Mg/Mg layer by magnetron sputtering

Abstract

Magnesium alloys are attracting increasing attention for the fabrication of temporary implants because of their superior biodegradability and biocompatibility. However, their high degradation rate under physiological conditions limits their clinical applications. In this work, a Nb₂O₅/Nb₂O₅-Mg/Mg multilayer coating was prepared on the surface of AZ31 magnesium alloy by magnetron sputtering in order to improve its corrosion resistance. The microstructure and performance of the layers were studied by SEM, AFM, EDS, and XPS, and a scratch tester, nanoindenter, friction tester, and electrochemical workstation, using Nb₂O₅ monolayer coating as a control. The results show that these two coatings significantly improved the mechanical, tribological, and anticorrosion performance of AZ31 magnesium alloy. Compared with a Nb₂O₅ monolayer coating, the multilayer coating exhibits an increased adhesion by about 10.6 times, and a decreased wear rate and corrosion current density by one order of magnitude, meaning higher damage resistance. This study provides a feasible strategy for enhancing the properties of ceramic layers on magnesium alloys for medical applications.

Fig. 1. SEM sectional micrographs of coated Si specimens: (a) Nb₂O₅, (b) M-Nb₂O₅.

Fig. 2. SEM and 3D AFM images of the coating samples: (a) Nb₂O₅, (b) M-Nb₂O₅.

Fig. 3. XRD patterns of naked AZ31 and coated AZ31 specimens.

Fig. 4. Scratch curves, morphologies of scratch track, and the EDS spectrum taken from the specified location for the studied coatings: (a) Nb₂O₅, (b) M-Nb₂O₅.

Fig. 5. SEM pictures and section profiles of the wear track of specimens: (a) naked AZ31, (b) Nb₂O₅ and (c) M-Nb₂O₅.

Fig. 6. Polarization curves of un-coated and coated AZ31 alloys in SBF solution.

Fig. 7. (a) Nyquist plots, (b) Bode impedance and (c) phase angle plots, and (d) corresponding EC of bare AZ31 alloy and coating samples in SBF solution.

Fig. 8. SEM micrographs and EDS results at specific locations of the specimens after polarization experiments: (a) naked AZ31, (b) Nb₂O₅ and (c) M-Nb₂O₅.