Microstructure and degradation performance of biodegradable Mg-Si-Sr implant alloys

- Mg2Si, Mg17Sr2, MgSiSr and MgSi2Sr are present in the Mg rich corner alloys.
- Intermetallic size and morphology depends on the solidification sequence.
- Mass loss and potentiodynamic polarization tests show similar degradation trends.
- The intermetallics, impurities and alloy content influence the degradation rate.

In this work the microstructure and degradation behavior of several as-cast alloy compositions belonging to the Mg rich corner of the Mg-Si-Sr system are presented and related. The intermetallic phases are identified and analyzed describing the microstructure evolution during solidification. It is intended in this work to obtain insight in the behavior of the ternary alloys in in vitro tests and to analyze the degradation behavior of the alloys under physiologically relevant conditions. The as-cast specimens have been exposed to immersion tests, both mass loss (ML) and potentiodynamic polarization (PDP). The degradation rate (DR) have been assessed and correlated to microstructure features, impurity levels and alloy composition. The initial reactions resulted to be more severe while the degradation stabilizes with time. A higher DR is related with a high content of the Mg17Sr2 phase and with the presence of coarse particles of the intermetallics Mg2Si, MgSiSr and MgSi2Sr. Specimens with a higher DR typically have higher levels of impurities and alloy contents.

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