Realization and characterization of double-layer Ca-P coating on WE43 Mg alloy for biomedical applications

Biodegradable magnesium (Mg) and some of its alloys are expected to degrade in the human body in consort with the bone tissue healing process. However, the rapid corrosion rate of Mg and its alloys in the physiological environment hinder their applications as implant materials. In this study, we fabricated a double-layer Ca-P coating on the surface of WE43 Mg alloy with enhanced corrosion resistance. The WE43 alloy was firstly anodized and then coated with dicalcium phosphate dihydrate (CaHPO4·2H2O, DCPD) and hydroxyapatite (Ca10(PO4)6(OH)2, HA) layers, consecutively. The coating morphologies and mechanical properties of the DCPD- and HA-coated samples were characterized using SEM, XRD, FTIR, microhardness and pull-out tests. The corrosion behavior of the coated and uncoated samples was assessed by immersion in modified simulated body fluid (m-SBF) and potentiodynamic polarization tests. Results indicated that the DCPD coating was transformed into a compact and crack-free HA coating through an alkali treatment. The microhardness and adhesion strength of the HA-coating were significantly enhanced compared to the other samples. The HA-coated WE43 exhibited the lowest hydrogen gas evolution, degradation rate and the highest corrosion resistance in m-SBF among all samples.