Relationship Between Structure and Functional Properties of Ultrafine-Grained Fe-Mn-Si Alloys for Temporary Implants

This paper presents a study of microstructure formation in bioresorbable Fe-Mn-Si alloys for temporary implants under high-pressure torsion (HPT) at room temperature and at 300 °C. The effect of silicon on the mechanism of microstructure formation under HPT and, as a consequence, on the mechanical, corrosion and biological properties of the alloys is studied. It is established that Si promotes martensitic transformation. HPT leads to an increase in the microhardness values of the studied alloys from ~1560 MPa in the initial state to ~5500 MPa (160–560 HV) due to structure refinement and phase transformation. An increase in the electrochemical corrosion rate of Fe-Mn-Si alloys to ~0.5 mm/year is established due to grain refinement to nanosize and the formation of strain-induced martensite. In vitro cytotoxicity and induced hemolysis studies showed that Fe-Mn, Fe-Mn-3.7Si, and Fe-Mn-5Si alloys after annealing and HPT can be characterized as biocompatible.