Tailoring degradation and biomineralization of Mg–Nb composites via micro-galvanic effects

In this work, Mg–niobium (Nb) composites containing 0–20 wt.% Nb were systematically developed to elucidate the correlation between Nb content, corrosion resistance, and in vitro biomineralization behavior in simulated body fluid (SBF). Electrochemical measurements, including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS), were complemented by long-term immersion and detailed microstructural and surface characterization. The results reveal a pronounced non-linear dependence of corrosion performance on Nb content. Among the investigated compositions, the Mg–15Nb composite exhibited the most favorable electrochemical response, delivering the highest film resistance (R f ≈ 1210 Ω·cm²), the highest polarization resistance (R p ≈ 1360 Ω·cm²), and the lowest corrosion current density (I corr ≈ 0.52 × 10⁻⁴ A/cm²), representing a substantial improvement over monolithic Mg. This enhanced electrochemical stability is consistent with immersion findings, in which Mg–15Nb exhibited a significantly reduced degradation rate (∼0.5 mm/y) compared to monolithic Mg (∼2.5 mm/y). Microstructural and surface analyses indicate that Mg–15Nb exhibits a relatively homogeneous Nb distribution and refined grains, accompanied by the formation of a dense and comparatively continuous Ca–P-rich corrosion-product layer, with HAP-related diffraction features identified by XRD and carbonate- and phosphate-related functional groups detected by FTIR. This favorable surface evolution and enhanced in vitro biomineralization are consistent with a contribution from micro-galvanic interactions inferred from the combined electrochemical, microstructural, and surface-characterization results. In contrast, increasing the Nb content to 20 wt.% is associated with pronounced particle clustering and a corresponding deterioration in electrochemical performance, in vitro biomineralization capability, and corrosion resistance, consistent with more localized electrochemical activity and an inferred contribution from micro-galvanic interactions. Overall, 15 wt.% Nb represents the most favorable composition within the selected powder-metallurgy processing conditions for balancing degradation control and in vitro biomineralization capability.