Effect of silver in thermal treatments of Fe-Mn-C degradable metals: Implications for stent processing

Abstract

Twinning-induced plasticity (TWIP) steels are considered excellent materials for manufacturing products requiring extremely high mechanical properties for various applications including thin medical devices, such as biodegradable intravascular stents. It is also proven that the addition of Ag can guarantee an appropriate degradation while implanted in human body without affecting its bioactive properties. In order to develop an optimized manufacturing process for thin stents, the effect of Ag on the recrystallization behavior of TWIP steels needs to be elucidated. This is of major importance since manufacturing stents involves several intermediate recrystallization annealing treatments. In this work, the recrystallization mechanism of two Fe-Mn-C steels with and without Ag was thoroughly investigated by microstructural and mechanical analyses. It was observed that Ag promoted a finer microstructure with a different texture evolution, while the recrystallization kinetics resulted unaffected. The presence of Ag also reduced the effectiveness of the recrystallization treatment. This behavior was attributed to the presence of Ag-rich second phase particles, precipitation of carbides and to the preferential development of grains possessing a {111} orientation upon thermal treatment. The prominence of {111} grains can also give rise to premature twinning, explaining the role of Ag in reducing the ductility of TWIP steels already observed in other works. Furthermore, in vitro biological performances were unaffected by Ag. These findings could allow the design of efficient treatments for supporting the transformation of Fe-Mn-C steels alloyed with Ag into commercial products.

Microstructural Parameters of Cold‐Rolled and Annealed Fe–24Mn–3Al–1Ni–2Si–0.06C Steel Obtained by X‐Ray Diffraction

“…This interaction does not inhibit recrystallization due to the high dislocation density obtained after cold-rolling Twip steel. According to literature, [20,36] a wide temperature range was expected between the start and finish of recrystallization temperature when precipitation occurs during recovery and recrystallization. To support the precipitation discussion, the first derivative curves obtained from dilatometric tests after cold rolling are in the supplementary material, Figure S1 (Supporting Information).…”

“…[6,18,19] Recently, recrystallization was investigated in Twip steel after various heat treatments, aimed to obtain a satisfactory microstructure and improved mechanical properties. [20,21] A quantitative estimation of dislocation density, stacking faults, and twin probability can be obtained by X-Ray diffraction (XRD). XRD provides an average representation of data in a larger area and, although influenced by stacking faults, twins, texture, and instrumental parameters, this technique has been successfully used.…”

“…[ 6,18,19 ] Recently, recrystallization was investigated in Twip steel after various heat treatments, aimed to obtain a satisfactory microstructure and improved mechanical properties. [ 20,21 ]…”

Effects of Different CO2 Concentrations and Degradation Media on Static Corrosion of Commercially Pure Zinc

“…The introduction of Mn allowed the increase of the degradation rate of Fe-based alloys, so that the corrosion rate would span in the range 515-520 µm/year, about twice faster than that of pure Fe [8,9]; this was found for an Fe-12Mn-1.2C alloy, leading to a general improvement of the mechanical properties and to a lower corrosion rate, approximatively of 0.20 ± 0.05 mm/year [10]. The formation of a degradation product layer on sample surfaces, after static degradation tests, especially for higher amounts of Mn, was assessed considering different environmental conditions, such as 5 vol.% CO 2 [11][12][13]. However, even the corrosion rate of this group of alloys, with or without C, is generally considered too low for many temporary implant applications [3].…”

Plasma Immersion Ion Implantation of a Fe-Mn-C Based Steel for Biomedical Applications: Effect of Gases and Treatment Times on the Surface Properties

“…In particular, focus was recently directed on alloying and microstructural leveling to meet biocompatibility and biodegradability requirements, and the modulation of the surface-medium interface in corrosion and cytocompatibility processes [5,6]. Fe-Mn-C steels were expressly designed to present a corrosion rate higher than regular Fe-Mn alloys, without inducing sensible cytotoxicity [7]. Recent advances highlighted the importance of surface-medium interface in corrosion and cytocompatibility [8].…”