Grain size evolution and mechanical properties of thermomechanically processed pure iron for biodegradable medical implant application

A high strength-ductility combination is a critical mechanical property requirement for biodegradable metals such as pure iron (Fe) deployed for cardiovascular implant applications. However, improving strength and ductility simultaneously is a very challenging task because strength and ductility are mutually exclusive. The main target of this work was to achieve homogeneous and fine grain structure in pure iron (Fe) that would enable adequate strengthductility combination via thermomechanical process of cold rolling and recrystallization annealing. Pure Fe samples were subjected to various degrees of cold rolling followed by recrystallization annealing at 550°C, 670°C, 800°C and 900°C, microstructural examination and the mechanical property evaluation. Thermomechanical processing restored ductility, refined microstructure reducing grain size from 29.6 µm to 14.6 µm and 13.8 µm, which led to 44.7% and 48.2% increase in yield strengths for the pure Fe cold rolled to 75% and 85% reduction and annealed at 550°C, respectively.Keywords: grain size evolution, mechanical properties, pure iron, thermomechanical processing, biodegradable