Microstructures and degradation mechanism in simulated body fluid of biomedical Mg-Zn-Ca alloy processed by high pressure torsion

In this paper, biomedical Mg-Zn-Ca alloy was processed by high pressure torsion (HPT) up to a maximum of 5 revolutions at room temperature and 7.5 GPa. The microstructures of as-received material and HPT material were studied, as well as the corrosion properties and degradation mechanism of the alloy immersed in simulation body fluid (SBF). It revealed that the average grain size of as-received material was 11 mu m and most of the second phases distributed along the grain boundaries. The corrosion pits formed near the grain boundaries where the corrosion rate was much faster than that of other areas. After HPT processing for 5 revolutions, not only the grain size was significantly refined to 130-150 nm, but also the second phases distributed uniformly. These microstructural variations caused the entire surface of the alloy corroded almost at the same corrosion rate. The corrosion interface of the center region and the edge region presented the uniform and gentle profile curve without any obvious corrosion pits. The HPT material in SBF tended to degrade by uniform corrosion mode. (C) 2016 Published by Elsevier Ltd.