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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 e 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.

Powder sintering at 1200 &deg, C for 180 min was used to produce Fe&ndash, 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&ndash, Mn alloys was investigated. The Fe&ndash, 35Mn alloy with a microstructure dominated by the Austenite phase showed the best set of tensile properties, including ultimate tensile strength and Young&rsquo, s modulus, suitable for orthopaedic implant applications. The fracture surface of the Fe&ndash, 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.

Among iron-based materials, the Fe-Mn system appears to be highly suitable for the development of biodegradable metals for orthopaedic and vascular applications. The versatility of tailoring such steels by alloying provides many opportunities to customise biodegradable devices. In the field of applications where a high load-bearing capacity is required, the addition of Si could constitute an effective strategy to improve the mechanical properties while maintaining a similar corrosion susceptibility and biocompatibility. In this study, the microstructure, mechanical properties, and corrosion behaviour of Fe-30 Mn-5Si (wt.%) alloy are presented, discussed, and assessed in comparison with a binary Fe-30 Mn formulation. Emphasis is placed on characterising the alloys in processed conditions by using conventional thermomechanical rolling and annealing techniques, which are feasible and allow for scale-up. Such techniques affect phases equilibrium, internal stresses and grain size, thus altering the degradation behaviour. The addition of Si resulted in excellent microstructural homogeneity and was used to tailor the relative abundances of austenitic and martensitic phases by applying different heat treatment strategies. As a result, the mechanical resistance was improved by 70 % compared to the base alloy, the strain hardening ability was improved while keeping good ductility. Electrochemical corrosion tests and static degradation experiments showed that both alloys corrode at a similar rate, although the addition of Si appeared to induce a slower degradation in the initial stage and a faster one in the long term.

WOS: 000266117900037 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 Mossbauer spectroscopy. Experiments reveal that two types of thermal-induced martensites, epsilon(h.c.p.) and alpha'(b.c.c.) martensites, form in the as-quenched alloys and these transformations have athermal characters. The Mo or Co (5 wt%) addition to the Fe-13%Mn alloy does not change coexistence of epsilon and alpha' martensites between 10-15 wt%Mn content. However, it stabilizes the parent phase leading to the depression of the transformation temperatures. In addition, Mossbauer spectra of the alloys reveal a paramagnetic character with a singlet for the gamma(fc.c.) austenite and epsilon martensite phases and a ferromagnetic character with a broad sextet for alpha' martensite phase. The volume fractions of the phases change and the amount of alpha' 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. (C) 2008 Elsevier B.V. All rights reserved.

This article, which continues the series started by Cotes et al. (Metall. Mater. Trans. A , 1995, vol. 26A, p. 1957-69), presents a study of the energetics of the heterogeneous nucleation of hcp martensite in the fcc matrix of the Fe-Mn system. A major goal of the work is the exploration of the various qualitative and quantitative consequences of applying the Olson and Cohen approach (OCA) to the most reliable information on the Fe-Mn system. To this end, an extensive assessment of the quantities involved in the OCA is performed. The selected Gibbs energy and the lattice parameter descriptions for fcc and hcp are based on recent experimental studies. Explicit calculations are presented of the key quantities in the OCA, including those quantities that have not yet been measured. In particular, a probable range of values is established for the surface energy parameter σ, which plays a crucial role in the treatment of the nucleation size. On these bases, values are derived for the probable number of atomic planes ( n C) of the embryo, which, according to the OCA, is at the condition of spontaneous growth. Predictions of the Mn content upon n C are also reported. The present attempt to calculate in detail the energetics of the fcc -hcp martensitic transformation also revealed the lack of thermophysical data for Fe-Mn alloys. The need for experimental studies of various relevant quantities is emphasized., Facultad de Ciencias Exactas

Clear experimental evidence of re-entrant spin glass state has been revealed in Er doped CeFe2 compounds. The zero field cooled - field cooled bifurcation in dc magnetization, frequency dependence of freezing temperature, relaxation in zero field cooled magnetization and presence of large remanence confirm the spin glass state in these compounds. Frequency dependence is found to follow the critical slowing down mechanism. The random substitution of Er and the change in the valence state of Ce along with an enhancement of the ferromagnetic component in the Fe sublattice seem to be responsible for the spin glass state. Using detailed experimental protocols, we also prove that the low temperature state in these compounds is not a magnetic glass. The absence of exchange bias gives an indication that there is no coexistence of ferromagnetism and spin glass state in these compounds. The RSG state is found to be associated with the randomly magnetized clusters instead of atomic level randomness., 19 pages, 9 figures

We calculate the electronic properties of austenite and martensite Fe-9%Mn alloys using the self consistent full-potential linearized-plane-wave method under the generalized gradient approximation full lattice relaxation. By minimizing total-energy, the lattice constants in their ground states were determined. We discuss the total energy dependence of the volume, and density of states (DOS). © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2008., 43, This work was supported by the Dumlupınar University within research Project No. 43.