Simulating Polarization Curves of Commonly Identified Intermetallic Particles from High Strength Aluminum Alloys Via First Principles
Authors: Li Sirui , Zhu Yakun , Taylor Christopher , Frankel Gerald S. 
Published: February 2020

In this talk, first principles density functional theory (DFT) implemented in the Vienna Ab-initio Simulation Package (VASP) is coupled with micro-kinetic modeling to simulate the polarization curves of some commonly identified intermetallic particles (IMPs). First principles DFT calculation is used to characterize the adsorption energies for the cathodic reaction intermediates on intermetallic surfaces. The species include atomic oxygen (O) and hydroxyl (OH) as intermediates for the oxygen reduction reaction. We will show that when coupling the ground state energy calculations with an appropriate micro-kinetic model[1–4], we can simulate simple polarization curves of the IMPs. One of the most desirable properties obtained from the simulated polarization curve is corrosion potential of the IMPs. Corrosion potential can indicate the relative nobilities of IMPs with respect to the alloy matrix. Experimentally the corrosion potential of IMPs on the range of microns are measured via a micro-capillary cell technique. On the simulation side, however, a method that can be directly compared to experimental data has not yet been fully realized. Whereas attempts to estimate corrosion potentials from the surface work functions obtained by DFT calculations have been made in recent literature [7]. we contend here that a model founded in electrode kinetics will be more successful in bridging simulation and experiment.

We started with Al7FeCu2, one of the most commonly identified cathodic IMP in high strength aluminum alloy. Our simulated for this IMP is -336.7 mV vs NHE, which is in good agreement with experimental data: -307 mV vs NHE[5]. We also aim to extend our current model to more reactive IMPs that contain Mg, such as Mg2Si and MgZn2, since these particles are measured to be more anodic than the aluminum matrix. For Mg containing particles, the cathodic reaction is the hydrogen evolution reaction (HER), and the reaction mechanism on the atomic scale has been proposed by Taylor[6]. Results for both anodic and cathodic particles based on the above DFT plus microkinetic model will be presented in this presentation.

Reference:

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[6] C.D. Taylor, A First-Principles Surface Reaction Kinetic Model for Hydrogen Evolution under Cathodic and Anodic Conditions on Magnesium, J. Electrochem. Soc. 163 (2016) C602–C608. doi:10.1149/2.1171609jes.

[7] Y. Zhu, J. Poplawsky, S. Li, R. Unocic, C. D. Taylor, J. Locke, E. Marquis, G. S. Frankel, Probe to the localized corrosion on/around nm-scale hardening precipitates in Al-Cu-Li alloys, in preparation.