41 research outputs found
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 αⳠformation, 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}ă113ă twinning system was observed to be activated by electron backscattered diffraction analyses
New method to characterize a machining system: application in turning
Many studies simulates the machining process by using a single degree of
freedom spring-mass sytem to model the tool stiffness, or the workpiece
stiffness, or the unit tool-workpiece stiffness in modelings 2D. Others impose
the tool action, or use more or less complex modelings of the efforts applied
by the tool taking account the tool geometry. Thus, all these models remain
two-dimensional or sometimes partially three-dimensional. This paper aims at
developing an experimental method allowing to determine accurately the real
three-dimensional behaviour of a machining system (machine tool, cutting tool,
tool-holder and associated system of force metrology six-component
dynamometer). In the work-space model of machining, a new experimental
procedure is implemented to determine the machining system elastic behaviour.
An experimental study of machining system is presented. We propose a machining
system static characterization. A decomposition in two distinct blocks of the
system "Workpiece-Tool-Machine" is realized. The block Tool and the block
Workpiece are studied and characterized separately by matrix stiffness and
displacement (three translations and three rotations). The Castigliano's theory
allows us to calculate the total stiffness matrix and the total displacement
matrix. A stiffness center point and a plan of tool tip static displacement are
presented in agreement with the turning machining dynamic model and especially
during the self induced vibration. These results are necessary to have a good
three-dimensional machining system dynamic characterization
Improvement of Superelastic Performance of Ti-Nb Binary Alloys for Biomedical Applications
International audienceRecently, beta-Ti-based alloys consisting of non-cytotoxic elements and possessing a low elastic modulus attracted considerable attention for biomedical applications. In addition to low elastic modulus, these alloys must also present a high strength level required to endure stresses. However, it is not easy to find a thermomechanical route in order to achieve low elastic modulus and high strength simultaneously. In this study, we show that severe cold-rolling deformation followed by a short aging treatment on Ti-Nb binary alloys, in order to produce ultrafine grains and/or omega phase, is an effective way to improve both strength and superelasticity. High stress (900 MPa), low modulus (35 GPa), and high recoverable strain (2.5%) are obtained using this route. The obtained results on mechanical properties are explained in relation with microstructure evolution during thermomechanical processing
A thermo-mechanical treatment to improve the superelastic performances of biomedical Ti-26Nb and Ti-20Nb-6Zr (at%) alloys
International audienc
Influence of a short thermal treatment on the superelastic properties of a titanium-based alloy
International audienc
Superelastic property induced by low-temperature heating of a shape memory Tiâ24Nbâ0.5Si biomedical alloy
International audienceIn this study, we have explored a new way to obtain a superelastic titanium-based alloy. Contrary to the classical method consisting to obtain the ÎČ microstructure directly by water quenching from the high temperature ÎČ-phase domain, this way consists in obtaining first a shape memory alloy displaying a fully α'' martensitic microstructure and then a superelastic behavior after applying a low temperature heating
In situ synchrotron X-ray diffraction study of the martensitic transformation in superelastic Ti-24Nb-0.5N and Ti-24Nb-0.5O alloys.
International audienceMechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compns. of metastable ÎČ titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to det. the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic ÎČ titanium alloys. Synchrotron X-ray diffraction (SXRD) expts. proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the ÎČ phase to the α'' phase. The evolution of vol. fraction of α'' martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a non-conventional behavior. SXRD expts. showed a huge ability of the ÎČ phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the ÎČ phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the ÎČ phase and a reversible SIM transformation. In both alloys, the lattice parameters of the α'' martensite evolve similarly in accordance with the initial texture of the ÎČ phase and the crystallog. of the transformation
Elaboration et caractérisation d'alliages de type Ti-Nb-X (X = O, N) pour des applications biomédicales Synthesis and characterisation of Ti-Nb-X (X = O, N) alloys for biomedical application
Dans cette Ă©tude, trois alliages de titane ÎČ-mĂ©tastables de composition Ti-27Nb, Ti-24Nb-0.5N et Ti-24Nb-0.5O ont Ă©tĂ© Ă©laborĂ©s par fusion. Ces trois alliages prĂ©sentent des propriĂ©tĂ©s superĂ©lastiques lors des essais de traction. Des essais de traction in-situ sous rayonnement synchrotron nous ont permis de monter que cette superĂ©lasticitĂ© est due Ă une transformation martensitique rĂ©versible ÎČ â αâ bien connue pour deux alliages alors que celui contenant de l'oxygĂšne prĂ©sente un comportement moins conventionnel. Les tempĂ©ratures caractĂ©ristiques (MS, MF) de la transformation martensitique ÎČ (austĂ©nite) vers αâ (martensite) et celles (AS, AF) de la transformation inverse αâ vers ÎČ ont aussi Ă©tĂ© dĂ©terminĂ©es par des essais mĂ©caniques dynamiques. Ces tempĂ©ratures caractĂ©ristiques augmentent linĂ©airement avec la contrainte externe et cette augmentation suit la relation de Clausius Clapeyron. <br> Ti-Nb based alloys are well known to their good mechanical properties, shape memory effect, superelasticity, as well as good biocompatibility. Our study is focused on the improvement of their mechanical properties by adding alloying element such as oxygen or nitrogen. Superelasticity was drastically improved by addition of a few amount (0.5 at %) of oxygen or nitrogen. Martensitic transformation between the ÎČ parent phase (austenite) and αâ product phase (martensite), responsible for the superelastic property, has been extensively studied by Dynamic Mechanical Analysis (DMA) and in-situ tensile test under X-ray synchrotron diffraction