Microstructure and properties of Nb2O5/Mg gradient coating on AZ31 magnesium alloy by magnetron sputtering

Abstract

A Nb 2 O 5 /Mg gradient coating was synthesized on AZ31 magnesium alloy through the magnetron sputtering technique. The microstructure and properties of the coating were investigated by SEM, AFM, EDS and XPS, scratch tester, nanoindenter, friction tester, and electrochemical workstation, with a Nb 2 O 5 monolayer coating as a control. The results show that all the as-disposed films have an amorphous columnar structure, and can improve the mechanical, anti-wear and anti-corrosion properties of AZ31 magnesium alloy. The Nb 2 O 5 /Mg gradient coating shows a gradual change in chemical composition through its depth, decreasing the residual stress of the coating/substrate system, thus reducing the risk of film cracking, and increasing compactness of the coating. Compared with a Nb 2 O 5 single-layer film of the same thickness, the gradient coating exhibits increased adhesion, H/E and H 3 /E 2 increased by about 16 times, 7.8% and 100% respectively, and a wear rate reduced by more than an order of magnitude. In addition, the gradient coating has better corrosion resistance, having a two orders of magnitude lower current density and one order of magnitude higher polarization resistance. This study provides a workable strategy for improving the performance of ceramic coatings on magnesium alloy, for medical applications. • Nb 2 O 5 /Mg gradient coating was applied to AZ31 magnesium alloy using magnetron sputtering. • The gradient coating is compact, without cracks. • The gradient coating show higher adhesive, mechanical, and anti-corrosion properties than the monolayer coating.