Monitoring of the microstructures and compositions of Mg-Zn-Ca Alloys to control degradation and hydrogen evolution for biodegradable implants

摘要

This work studied the corrosion behavior of Mg-Zn-Ca alloys of different microstructures in simulated body fluids to understand corrosion mechanism and their relationship with solidification behavior. Magnesium and its alloys are being considered as very promising biocorroding materials but their degradation in body fluid media comes together with hydrogen generation which is a huge challenge. Especially there is still a lack of information about the degradation level related to the grain size. The aim of this work was to investigate the possibility of controlling grain size to allow the monitoring of the degradation itself to forecast life time of implants. In addition by controlling degradation, hydrogen evolution may be prognosticated and kept in acceptable predictable ranges. This work reports on the degradation of two (Zn-poor and Zn-rich) Mg-Zn-Ca crystalline alloys produced by mold casting yielding different kinds of microstructures with several sizes. The dependence of corrosion rates and hydrogen evolution on the alloy composition and on the size and kind of microstructure were analyzed in comparison with amorphous alloys of similar compositions. Zn-rich composition with average grain sizes of-190 nm presented much lower and acceptable levels of hydrogen evolution. This was explained by the higher stability of the oxide film. Mg-Zn-Ca crystalline alloys with Zn-alloying threshold and homogeneous grain size (<500 nm) appear of great interest for use as implants.