Microstructure characteristics, degradation behaviors and film formation mechanism of Zn-1Mg-0.25Nd-xSn in the Kokubo's electrolyte

Till now, the novel Zn-based alloys have attracted extensive attention, due to the excessive dissolution rate in the Mg-based alloys and the detrimental products in the Fe-based biomaterials. In this study, the novel degradable Zn-1 Mg-0.25Nd-xSn alloys were fabricated, and the microstructure, degradation and film formation mechanism were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analyzer (EPMA), atomic force microscopy (AFM), confocal laser scanning microscopy (3D/CLSM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the morphology of interdendritic beta-lamellar and primary eta Zn obviously changed as the Sn contents increased, whilst the corrosion initiates as a consequence of relative Volta potential differences between the Zn-rich and micro-eutectic phases. Therein, the optimalizing corrosion rate was obtained in the Zn-1 Mg-0.25Nd-0.3Sn, which was associated with the formation of insoluble Zn-5(OH)(8)Cl-2, Zn-3(PO4)(2), Sn(OH)(2)/Sn(OH)(4), reducing the reaction activities of the Zn matrix. Besides, the REs-rich products incorporated into the passive layer and absorbed OH-, forming a uniform and dense degradation layer. However, as the Sn contents further increased, the formation of abundant micro-galvanic nucleation sites facilitates the metastable pits dissolution and the probability of transition from metastable to stable.

Automated summary

Novel degradable Zn-1 Mg-0.25Nd-xSn alloys were fabricated and investigated for their microstructure, degradation, and film formation mechanism using various microscopy techniques. The optimal corrosion rate was observed in the Zn-1 Mg-0.25Nd-0.3Sn alloy, attributed to the formation of insoluble compounds and reduction in reaction activities of the Zn matrix. Incorporation of rare earth products into the passive layer also contributed to the uniform and dense degradation layer.