Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys

International audienceIn this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α″ formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332}〈113〉 twinning system was observed to be activated by electron backscattered diffraction analyses

Investigation of early stage deformation mechanisms in a metastable β titanium alloy showing combined twinning-induced plasticity and transformation-induced plasticity effects

International audienceAs expected from the alloy design procedure, combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects are activated in a metastable β Ti-12(wt.%)Mo alloy. In-situ Synchrotron X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) observations were carried out to investigate the deformation mechanisms and microstructure evolution sequence. In the early deformation stage, primary strain/stress induced phase transformations (β->ω and β->α'') and primary mechanical twinning ({332} and {112}) are simultaneously activated. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {332} twinning and the subsequence secondary mechanisms dominate the early stage deformation process. The evolution of the deformation microstructure results in a high strain hardening rate (~2GPa) bringing about high tensile strength (~1GPa) and large uniform elongation (> 0.38)

Superelastic Behavior of Biomedical Metallic Alloys

In this this work, superelastic NiTi and Ni-free Ti-23Hf-3Mo-4Sn biomedical alloys were investigated by tensile tests in relationship with their microstructures. To follow the stress-induced martensitic transformations occurring in these alloys, in situ tensile tests under synchrotron beam were conducted. In NiTi, an intermediate trigonal R phase, which is first stress-induced before the B19 ' martensitic phase, was identified. However, the Ti-23Hf-3Mo-4Sn alloy does not present a transitional phase, and a direct beta into alpha '' reversible stress-induced martensitic transformation was observed. With NiTi, all the applied strain is recovered after unloading, and no residual plastic deformation occurs. However, the strain is not completely recovered with the Ti-23Hf-3Mo-4Sn alloy, and residual plastic strain was observed to prevent a complete recovery, thus explaining why the strain recovery is lower for Ti-23Hf-3Mo-4Sn compared with NiTi. We also showed that the maximum strain recovery depends on the texture in the Ti-23Hf-3Mo-4Sn alloy. The favorable texture leading to the highest strain recovery (4.6 pct) is the {111}< 110 and rang;(beta) texture, which can be obtained by a short-time solution treatment (0.3 ks) at 1073 K with this alloy

Red de monitoreo de eventos hidrológicos extremos en la vertiente sur del Río Salado, provincia de Buenos Aires

Se ha demostrado que los eventos hidrológicos extremos en la provincia de Buenos Aires constituyen una característica de la misma, considerando los balances de agua en el suelo (zona no saturada) de vital importancia. Estos balances indican que la cuenca del Río Salado es la más sensible a los excesos hídricos, y la región sudoeste de la provincia, la más perjudicada durante las deficiencias hídricas (Scarpati y Capriolo, 2013). Por ello toman importancia las tareas de prevención como son las obras civiles y las redes de monitoreo de las condiciones principales que intervienen en este tipo de fenómenos, con el fin de dar alerta a las autoridades competentes ya sea en períodos de inundaciones o de sequías. Una red de monitoreo comprende las actividades relativas a la recolección de datos, diseñados y procesados con un objetivo definido (Guía de prácticas hidrológicas, 1994). Consiste en un arreglo de sensores que conforman las estaciones y en un sistema de comunicación que permite la transmisión de los datos a los centros de monitoreo. Su principal función es el estudio de procesos fundamentales que se dan en el medio ambiente, como así también proveer alerta de amenazas, como por ejemplo de inundaciones, erupciones volcánicas, terremotos, tsunamis, etc. (Hart y Martinez, 2006). El monitoreo y la recolección de datos hidro-meteorológicos es importante debido a que los eventos naturales como precipitaciones, temperaturas, velocidades del viento, entre otros, son irrepetibles en la naturaleza (Fattorelli y Fernández, 2011). El diseño de una red hidro-meteorológica comprende principalmente el conocimiento hidrológico y climático de la zona en la cual se establecerá

Preparation of H-bar cross-sectional specimen for in situ TEM straining experiments: a FIB-based method applied to a nitrided Ti-6Al-4V alloy

International audienceThe in situ tensile straining of cross-sectional specimens inside a TEM is intrinsically very difficult to perform despite its obvious interest to study interfaces of surface treated materials. We have combined a FIB-based method to produce H-bar specimens of a nitrided Ti-6Al-4V alloy and in situ TEM straining stage, to successfully study the plastic deformation mechanisms that are activated close to the nitrided surface in the Ti-based alloy

Microstructure, thermo-mechanical properties and Portevin-Le Chatelier effect in metastable β Ti-xMo alloys

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