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Deep eutectic solvents (DESs) are green anhydrous solvents that have recently been proposed in sustainable non-aqueous metal electrodeposition processes. The use of DESs over aqueous solutions allows metal electrodeposition without significant side reactions, such as the evolution of hydrogen gas, which is responsible for embrittlement phenomena. In the current work, the electrolytic deposition of Fe-Mn alloys, which present good application in temporary biomedical devices, using DESs was assessed. Three DESs were studied: (a) choline chloride and ethylene glycol (ChCl/EG), (b) choline chloride and glycerol (ChCl/Gly), and (c) choline chloride and urea (ChCl/Urea). The physicochemical properties (viscosity and conductivity) of the three DESs of interest, with and without the presence of dissolved Fe and Mn salts, were thoroughly studied. Cyclic voltammetry analyses showed that the reduction potential of both metals was within the potential window for the three DESs studied, which allowed the successful electrodeposition of Fe-Mn alloys. The deposit obtained from the ChCl/Urea DES presented the highest amount of Mn (49.71 at%). The latter, as well as the fact that the ChCl/Urea based electrolyte showed good stability at T = 80 °C after four electrodeposition cycles, are promising indicators of the potential success of the use of non-aqueous electrodeposition of Fe-Mn alloys using DESs.

Fe–Mn alloys are promising candidates for less-invasive and temporary implants such as bioabsorbable stents. However, their composition and microstructure must be tailored to assess an adequate corrosion rate for the desirable lifespan of the stent. This study aimed to evaluate the development of Fe–Mn alloy and its structure and properties correlation when processed by electrodeposition. Planar samples were produced by potentiostatic deposition at two different potentials, −1.3 and −1.7 V vs. Ag/AgCl, from a chloride-based acidic electrolyte with different amounts of NH4Cl. It was verified that, in more negative deposition potentials, the deposition interface changes from planar to dendritic, leading to more ramified deposits with a high level of defects like cracks and pores. More negative potentials also increased the Mn content in the deposit from 0.8 to 5.2 wt.% Mn. The microstructure was composed of a single phase of (Fe, Mn) solid solution in the −1.3 V vs. Ag/AgCl deposit, while the deposit obtained at −1.7 V vs. Ag/AgCl exhibit two phases, one rich in Mn and the other rich in Fe. A higher concentration of NH4Cl in the electrolyte leads to an increase in the Mn content (5.2 wt.% Mn), maintaining the monophasic microstructure. Although several challenges still remain, these results prove that is possible to obtain Fe–Mn bioabsorbable alloys by electrodeposition, which opens a new processing route for these alloys.

The present work aims at exploring the influence of laser welding on the functional behaviour of a Fe-20Mn-0.6C (wt.%) bioabsorbable alloy. At first, the selection of the most suitable process speed (40 mm/s) was done in order to obtain a full penetration joint with limited taper. Then, microstructural and mechanical analyses of welded sheets confirmed suitable performance of the joint, without porosity, thus preserving chemical composition, mechanical resistance and ductility even after welding. In particular, the base material comprised both γ austenite and ε martensite, while the welded samples showed a further type of martensite, namely α’. Moreover, ultimate tensile strength (1095 MPa and 1104 MPa in base and welded material, respectively) and elongation to failure (61.3% and 60.9%, respectively) were almost not influenced by the welding process. Considering the absorbable nature of these alloys, static immersion degradation tests were carried out, and confirmed that the surface of the welded bead did not exhibit a significant variation of the material degradation rate after 14 days in modified Hanks’ solution. Finally, a significant accumulation of degradation products, mainly (Fe,Mn)CO3, was observed along the joining line.

Abstract This study investigated the sublimation of Mn and microstructural evolution of binary Fe/Mn compacts sintered at various temperatures in a vacuum. A high sintering temperature or a lengthy holding time promotes powder densification. Due to sublimation of Mn, the weight loss of the compacts mainly occurs during the isothermal holding stage of the sintering process; it increases significantly from 1.5 wt.% for sintering at 1000 °C to 8.6 wt.% at 1200 °C. For the first time, the phase evolution in the binary elemental compacts was clarified using in situ neutron diffraction. The γ-austenite phase emerges during temperature ramping to 536 °C, while β-Mn and α-Fe disappear at 774 °C and 881 °C. The neutron diffraction also revealed that single phase γ-austenite forms in the Fe-Mn compacts if the temperature is ≥ 881 °C. Highlights • In situ and real-time neutron diffraction was used to identify phase transition. • Sublimation behavior of Mn in Fe/Mn powder mixtures was investigated. • The sintered microstructure is related to sublimation of Mn. [ABSTRACT FROM AUTHOR]

The influence of a magnetic transition on Fe and Mn diffusion in bcc Fe–Mn alloys as a function of Mn concentration is studied combining experimental measurements and DFT-informed modeling. The radiotracer technique in combination with precise mechanical sectioning or ion-beam sputtering is used to determine the diffusion rates of 59Fe and 54Mn in a series of Fe–Mn alloys with up to 1.9 at.%Mn. The solvent and solute enhancement factors are determined. While the diffusion rates of Fe atoms are found to be almost independent on the Mn content in the Fe–Mn alloys in both para- as well ferro-magnetic states, Mn diffusion is strongly enhanced by an increase of Mn concentration in these alloys, especially in the paramagnetic state. The experimental findings are supported by theoretical results, which are analyzed in terms of an equilibrium vacancy concentration, atomic jump frequencies, Mn–vacancy binding energy, short-range ordering tendency and kinetic correlation factors. [Display omitted] [ABSTRACT FROM AUTHOR]

The deformation-intensified atomic Mn-related separation of the bcc solid solution has been found in FeMn alloys ( x = 4.5-9.9) subjected to ball milling using Mössbauer spectroscopy. In the near surrounding of iron atoms, the atomic separation is similar to that observed upon the annealing of the alloys in a temperature range of 400-500°С. It has been found that the deformation-intensified atomic separation leads to the stabilization of the bcc phase with regard to the α → γ transformation, as well as to the expansion of the field of the existence of the bcc phase during heating. [ABSTRACT FROM AUTHOR]

Abstract: Microstructure and texture evolution during cold rolling and subsequent annealing were studied in an Fe–22 wt.% Mn–0.376 wt.% C alloy. During rolling the deformation mechanisms were found to be dislocation slip, mechanical twinning, deformation-induced ε-martensite transformation and shear banding. At higher strains, the brass-type texture with a spread towards the Goss-type texture dominated. A decrease in the Cu- and S- components was attributed to the preferential transformation to ε-martensite in Cu- and S-oriented grains. The texture of ε-martensite was sharp and could be described as {1129}〈3362〉. The orientation relationship {111} γ //{0001} ε and 〈110〉 γ //〈11–20〉 ε between ε-martensite and austenite was observed but only certain variants were selected. On subsequent annealing, the ε-martensite transformed reversely to austenite by a diffusionless mechanism. Changes in length along rolling, normal and transverse directions on heating were anisotropic due to a combination of volume expansion and shape memory effects. The S-texture component increased significantly due to transformation from the ε-martensite. [Copyright &y& Elsevier]

Abstract: High Mn steels demonstrate an exceptional combination of high strength and ductility owing to their sustained high work hardening rate during deformation. In the present work, the microstructural evolution and work hardening of Fe–30Mn and Fe–24Mn alloys during uniaxial tensile testing at 293K and 77K were investigated. The Fe–30Mn alloy did not undergo significant strain-induced phase transformations or twinning during deformation at 293K, whereas these transformations were observed during deformation at 77K. A modified Kocks–Mecking model was successfully applied to describe the strain hardening behavior of Fe–30Mn at both temperatures, and quantitatively identified the influence of stacking fault energy and strain-induced phase transformations on dynamic recovery. The Fe–24Mn alloy underwent extensive ε martensite transformation during deformation at both test temperatures. An analytical micromechanical model was successfully used to describe the work hardening of Fe–24Mn and permitted the calculation of the ε martensite stress–strain curve and tensile properties. [Copyright &y& Elsevier]

Abstract: The effects of the Mo and Co on the magnetic properties and the characteristics of martensitic transformation of the Fe–Mn alloy have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimeter (DSC), and Mössbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, ɛ(h.c.p.) and α′(b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. The Mo or Co (5wt%) addition to the Fe-13%Mn alloy does not change coexistence of ɛ and α′ martensites between 10–15wt%Mn content. However, it stabilizes the parent phase leading to the depression of the transformation temperatures. In addition, Mössbauer spectra of the alloys reveal a paramagnetic character with a singlet for the γ(f.c.c.) austenite and ɛ martensite phases and a ferromagnetic character with a broad sextet for α′ martensite phase. The volume fractions of the phases change and the amount of α′ martensite increases significantly with the Mo or Co addition. Third element addition also influences internal magnetic field and particularly, the addition of the Mo considerably decreases the internal magnetic field in the Fe–Mn alloy. [Copyright &y& Elsevier]

Powder sintering at 1200 °C for 180 min was used to produce Fe–Mn based alloys with tensile properties and an elastic modulus suitable for biodegradable implant applications. The effect of the addition of manganese on the microstructure, tensile properties and fracture behaviour of the Fe–Mn alloys was investigated. The Fe–35Mn alloy with a microstructure dominated by the Austenite phase showed the best set of tensile properties, including ultimate tensile strength and Young's modulus, suitable for orthopaedic implant applications. The fracture surface of the Fe–35Mn alloy showed signs of complex multimode fracture behaviour, consisting of interconnected pores and large segments with signs of ductile fracture, including the presence of dimples as well as micro-voids. [ABSTRACT FROM AUTHOR]