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

Abstract

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.

GRAIN SIZE EVOLUTION, MECHANICAL AND CORROSION BEHAVIOUR OF PRECIPITATE STRENGTHENED Cu-Ni ALLOY

“…Grain size determination of an alloy is an important procedure for structural analysis, where certain degree of properties enhancement is established. Grain size is the fundamental structural characteristic that enhances the crystallinity of metals according to their physical and mechanical behaviour [16]. Mechanical properties like UTS, hardness, impact strength, and ductility have been reported to have linear relationship with fine grain size dispersal [17].…”

“…For decades, a wide range of processing procedures, including casting, forging, rolling, drawing, and extrusion, have been used along with heat treatment to modify the microstructure and improve the mechanical characteristics of metals used in various applications. The grain size distribution, as well as other parameters, are regulated in order to obtain excellent mechanical properties and corrosion resistance [16] [25]. The changes in the passive layer characteristics due to alloy processing techniques, environment, and impurity concentration, microstructural refinement of Cu-Ni alloy can result in a significant improvement in corrosion response [26].…”