CE08 - Matériaux métalliques et inorganiques et procédés associés

Interactions of Electric CUrrents and Microstructures Evolutions – ECUME

Submission summary

Applying an electric current to a metallic alloy is of great interest for designing improved materials. First, it allows an in situ monitoring of microstructure evolutions during heat or thermomechanical treatments. Second, it can be used to efficiently tune microstructures. However, despite the great potential of these methods, their full application up to a possible industrial scale requires a better basic understanding of the interactions between electric currents and microstructure evolutions. The aim of the present project is precisely to build a modeling framework at the scale of the microstructure following a phase field approach, that will be applied to two complementary situations where dedicated experiments will be performed on simple metallic alloys: (i) monitoring of phase transformations by electrical resistivity and (ii) transformation of microstructures by application of intense electric currents.

The phase field modeling will incorporate the concurrent action of the driving forces at play, namely free energies of the evolving phases, kinetics of the separating interfaces, elastic relaxation due to eigenstrains and, finally, electrokinetics and mass transport by electromigration. The model will encompass both the electric response of an evolving microstructure and its control by mass transport generated by intense applied currents. The model will be implemented in 3D, recreating realistic situations with complex 3D arrangements of precipitates and interfaces.

First, neglecting electromigration when the applied electric field is small enough, the model will be used to predict the average electric resistivity of a microstructure that emerges during a phase transformation. These simulations will go beyond the commonly used simple homogenization schemes, which cannot properly account for the highly inhomogeneous current densities generated by complex 3D arrangements of moving interfaces. More precisely, the model will be used to quantitatively analyze dedicated experiments in the Ti-15%Mo alloy. First, using the beta -> alpha transformation at high temperature, complex microstructures will be generated during isothermal or cyclic thermal treatments. Second, using the beta -> omega transformation at low temperature, isothermal treatments will be used to obtain microstructures with inhomogeneous Mo concentration fields. These microstructures will be characterized using electron microscopy (SEM, TEM) and High Energy Xray diffraction. The corresponding resistivity measurements will be performed and compared to the predictions of the phase field model.

Second, taking into account atomic transport by electromigration, the model will be able to investigate how an electric current can be used to control microstructural changes that occur during a phase transformation. We will in particular investigate the sensitivity of the structural response to the different experimental settings that can be used for the electrical current (direct, alternative, pulsed). A particular attention will be paid to the interplay between length scales that may be generated by pulsed currents and intrinsic length scales (diffusion length, precipitate size, inter-precipitate distance). The concurrent action of these length scales may generate particular morphologies and, thereby, offer a way to control the microstructures. Concerning the experiments, a new experimental setup will be designed to comply with the specificities of the different materials to be investigated (temperatures, heating and cooling rates and controlled atmosphere) and to offer the possibility to deliver continuous or pulsed currents. Investigations on the Fe-C system will focus on the propagation of ferrite/austenite interfaces and the impact of an applied current on the fast interstitial C atoms. Finally, investigations on the substitutional Fe-Cu system will be focused on the action of an applied current on the nucleation and growth mechanisms.

Project coordination

Yann Le Bouar (Laboratoire d'étude des microstructures)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IJL Institut Jean Lamour (Matériaux - Métallurgie - Nanosciences - Plasmas - Surfaces)
LEM Laboratoire d'étude des microstructures
MATEIS Matériaux : Ingénierie et Science

Help of the ANR 498,386 euros
Beginning and duration of the scientific project: January 2019 - 48 Months

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