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Contribution à l'étude du comportement pseudo-élastique d'un alliage bêta métastable applications aux arcs orthodontiques :

Abstract : Titanium alloys are generally used in aeronautics for their excellent specific strength. In biomedical engineering titanium alloys are appreciated for showing usually biocompatibility and often a weak modulus of elasticity. In orthodontics, moreover, one seeks for aptitude of shape recovering which is very marked in NiTi. However, these last alloys have a reduced ductility that limits the aptitude for working and requires the use of preformed arc. Metastable titanium Beta III, currently marketed in a strongly hardened state is an acceptable compromise between ductility, apparent elasticity modulus and aptitude of shape recovering. This explains its success since its marketing in the Eighties. In addition, it does not contain nickel and it is weldable. It owes its properties to its pseudoelasticity, which is seldom exploited apart from orthodontics. This pseudoelasticity is the result of a work hardening induced by the working process, here wiredrawing. In this work we studied the role of the microstructure on the pseudoelastic effect and sought the means of acting on this microstructure to improve the pseudoelastic effect. The elaboration of these alloys, in addition to the problems involved in titanium, is made difficult by the high melting point of molybdenum. This is why we chose to start from products in the form of wire - available on the market - and to ignore the composition parameter in our study. Thus the only remaining optimisation parameters are the phases involved, the size of grain and the work hardening of the alloy. The study showed that the increase in the grain size and the predeformation significantly improve the pseudoelastic effect, whereas the presence of a second phase reduces or even cancels this effect. Moreover the alloy maintains a good ductility which makes it well suited to working.
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Pascal Laheurte. Contribution à l'étude du comportement pseudo-élastique d'un alliage bêta métastable applications aux arcs orthodontiques :. Autre. Université Paul Verlaine - Metz, 2003. Français. ⟨NNT : 2003METZ027S⟩. ⟨tel-01749795⟩



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