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The European Journal of Orthodontics Advance Access originally published online on September 5, 2006
The European Journal of Orthodontics 2007 29(1):8-13; doi:10.1093/ejo/cjl038
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© The Author 2006. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved.
The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact journals.permissions@oxfordjournals.org.

Improvement of pseudoelasticity and ductility of Beta III titanium alloy—application to orthodontic wires

P Laheurte*, A Eberhardt**, MJ Philippe* and L Deblock***

* LETAM (CNRS—UMR 7078), Université de Metz
** LPMM (CNRS—UMR 7554), ENIM Metz
*** Private practice, Vandoeuvre-les-Nancy, France

Address for correspondence Dr P. Laheurte, LETAM/ISGMP, Université de Metz, Ile du Saulcy, 57 000 Metz, France. E-mail: laheurte{at}letam.sciences.univ-metz.fr


  Abstract

The pseudoelasticity of metastable Beta III titanium alloy (TMATM) used for orthodontic applications is obtained by cold wiredrawing. This wire has higher rigidity than cold-drawn NiTi (NitinolTM, superelastic NiTi SE) and lower recoverable deformation. The low ductility value of Beta III is due to the deformation imposed by wiredrawing. The aim of this research was to improve the behaviour of this alloy by modifying the microstructural parameters to decrease the rigidity and increase the recoverable deformation and ductility of the alloy. The effects of second phase precipitate, grain size, and deformation on the wire mechanical properties were also examined.

The isothermal precipitation of alpha ({alpha}) or omega ({omega}isoth) phases precludes the expression of the pseudoelastic effect. The presence of an {omega}isoth phase considerably increases fracture strength, whereas the {alpha} phase strongly decreases the ductility and adversely affects the strain recovery ({varepsilon}r).

To control the grain size, the growth of the recrystallized grains was studied by considering several parameters, which are known to have an influence on grain size, including the cold rolled strain, the temperature, the time of annealing, and the initial grain size. A structure with coarse grains, quenched from a temperature higher than the beta transus (Tß), associated with a plastic pre-deformation, contributed to an improved pseudoelastic behaviour, due to the presence of a reversible martensite phase ({alpha}'') induced by the pre-deformation.


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