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WEB Phase field modeling of TWIP beta-metastable titanium alloys

Friday (25.09.2020)
11:35 - 11:50 M: Modelling and Simulation 1
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Recently, new beta-metastable TRIP/TWIP titanium alloys have been developed that exhibit improved mechanical properties, i.e. high strength and ductility, accompanied by an unprecedented strain hardening for titanium alloys at ambient temperature. These mechanical properties are attributed to complex microstructures engendered by the mechanical destabilization of the initial bcc phase during deformation. Indeed, the microstructure features numerous twins following the peculiar {332}<11-3> twinning mode, specific to beta-titanium alloys, as well as orthorhombic alpha'' and simple hexagonal omega phases ensued from concomitant displacive transformations. Moreover, observations have revealed the possible activation of secondary deformation mechanisms, such as secondary twins and/or alpha'' inside primary twins.

In view of better understand the formation of the complex microstructures described above, we have developed a phase field model focusing on the {332}<11-3> twinning mode.

Phase field models proposed so far for deformation twinning exhibit several essential flaws preventing them to be applied in our case. First, some of them formulate the elastic energy using the small strain approximation. Considering the large shear componentes of the eigenstrain associated with twinning (~35% for {332}<11-3> twins), the use of the infinitesimal strain theory is not justified, in particular because the accommodation mechanism resulting from the crystalline rotations are not correctly accounted for. Second, the proposed models are all restricted to primary twinning by construction, meaning that the free energy landscape is built in such a way that it cannot allow the formation of secondary twinning.

In this work, we propose a phase-field model free of the first deficiency, relying on a finite strain formalism. We will show the capabilities of this model to simulate the formation and evolution of the complex microstructures observed in TWIP titanium alloys. In addition, a comparison with a model formulated in a small strain formalism will be presented to show the influence of the geometrical non-linearities introduced in the finite strains framework.

Finally, the analysis of particular locations in the microstructure where stresses and strain are the largest will suggest a further extension of the model to handle secondary twinning.

Prof. Benoit Appolaire
Institut Jean Lamour
Additional Authors:
  • Juba Hamma
  • Prof. Yann Le Bouar
  • Prof. Alphonse Finel