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Friction stir welding was used to produce butt joints on 6 mm thick plates of UNS S32101 lean duplex stainless steel, S32205 duplex stainless steel, and S32750 and S32760 superduplex stainless steels. Fully consolidated joints were achieved, with full penetration, using heat input of 1.37-1.50 kJ/mm. Specimens submitted to tensile testing performed perpendicular to the welding direction showed failure on the base metal, reflecting better mechanical performance of the welded joints. Furthermore, tensile testing along the joints revealed higher yield and tensile strengths in all cases, as well as increased elongation. Microstructural evaluation showed that there was pronounced grain refinement in the welded joints of all the materials studied, achieving grain sizes as small as 1 µm. The differences in the ferrite and austenite grain sizes in the stir zone, such as the degree of grain refinement, could be explained by the combination of dynamic recrystallization of austenite during the welding process and the recrystallization and growth of the ferrite grains, promoted firstly by the severe deformation and secondly by the high temperature inherent to the FSW process. Superduplex stainless steel FSW joints were more able to maintain a balanced microstructure, compared to conventional and lean duplex stainless steels, due to greater homogeneity of recrystallization in the welded joint.

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During friction stir welding or processing (FSP), temperature and deformation have influence on the final microstructure and mechanical properties. Studying microstructures before and after welding might help interpreting mechanical and corrosion resistance; however, microstructural evolution during the process remains unknown. In this study, a FSP model of pipeline steel plates was developed. Thermocouples were inserted in different positions and temperature cycles were collected during FSP. The collected data was used to complete the numerical model based on computational fluid dynamics (CFD). The CFD model simulated the material flow and heat transfer in FSP considering the material as a fluid. The standard error between the peak temperatures of the simulation and experimental results was below 1%. The model allowed correlating peak temperatures and cooling rates to the obtained microstructures after FSP. Numerical results showed that peak temperatures and dwell times in the stir zone were high enough to cause grain coarsening. This observation was demonstrated upon prior-austenite grain size measurements.

this study compared Zr-Mo alloys with commercial metallic biomaterials. it was observed that the Zr-Mo alloys exhibited favourable mechanical properties, particularly the Zr-10Mo alloy, which showed the highest strength to Young's modulus ratio among all evaluated metals. these alloys also exhibited the lowest magnetic susceptibilities, which are important for magnetic resonance imaging (MRi). However, both Zr-and ti-based metals yielded comparable artifacts. it was concluded that the magnetic susceptibility must differ considerably to afford significantly improved MRI quality owing to the increased importance of non-susceptibility-related artifacts when comparing materials with relatively similar magnetic susceptibilities. Metals are still competitive with other classes of materials in the application and development of medical implants in various fields of medicine, such as orthopaedics, neurology, cardiology, and dentistry. Owing to their combined properties, including strength and toughness, and the possibility of employing cost-effective manufacturing processes, metals are typically the best biomaterial choice when compared to ceramics and polymers, as well as composites. The use of metallic devices in the human body is usually required for the replacement and stabilization of damaged bone tissues in orthopaedic practice. The classical examples of such applications include temporary plates and screws, and permanent total hip replacements. Other applications include usage in vascular stents, aneurysm clips, pacemakers, dental implants, wire sutures, etc. 1-3. Despite being similar to Ti alloys, particularly in their physical metallurgy and other properties 4 , Zr-based alloys have received comparatively little attention as biomaterials. Zr and its alloys exhibit excellent biocompatibility, good corrosion behaviour, and favourable mechanical properties 5-11. Specifically, these alloys are suitable for applications in orthopaedic and dentistry owing to their low Young's modulus. A major issue associated with using metallic materials in long-term implants is the mismatch between the bone and the employed device. Rigid implants can promote the stress shielding effect and cause bone resorption, strongly affecting the medium-to long-term quality of the surgical intervention 12. Accordingly, alloys with a low Young's modulus have been targeted for this type of application 13,14. In this regard, Zr alloys are similar to Ti alloys. For instance, Guo et al. 10 reported a Young's modulus of only 44 GPa for a β-type Zr-12Nb-4Sn alloy, which is relatively close to that of human cortical bone (around 20 GPa 15) and is similar to as the best results reported for Ti alloys 16. More recently, increasing interest in Zr and its alloys has been justified by their reduced magnetic susceptibility, which has been claimed to reduce the magnetic resonance imaging (MRI) artifacts 7,10,11,17,18. MRI is a powerful non-invasive tool for medical diagnosis that relies on the nuclear magnetic resonance phenomenon. It presents a high spatial...

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