Abstract: Corrosion resistance has become an important factor to consider in integrated computational materials engineering, yet generating science-based indicators of corrosion resistance for hypothetical materials remains challenging. We explore the quantitative relations between work function and corrosion potential, taking a theoretical approach that considers the relation between these thermodynamic and kinetically-determined variables. The work function is a fundamental thermodynamic property of a metallic surface in isolation, whereas the corrosion potential is kinetically determined as the potential at which the rates of anodic and cathodic processes active on the metal surface are equal. The latter quantity is therefore time dependent, as well as dependent on the material, surface preparation, ageing/history and the environment. Reasoning from Mixed Potential Theory, we develop a rationale for the correlation between the corrosion potential and the electronic work function. Two distinct Born-Haber cycles for the anodic dissolution reaction are analyzed to allow calculation of a related quantity, the ionic work function, which embodies the energy of desorption for metal cations from an electrode. The ionic work function is not only highly correlated with, but of similar magnitude to the cation hydration energy. The theoretical analysis provided herein establishes the significance of not only the electronic work function, but also the ionic work function, cation hydration energy, cohesive energy and the ionization potential as co-descriptors for the corrosion resistance of candidate corrosion resistant metal alloys, with the role of the environment to be considered in future work.

Abstract: In this talk, first principles density functional theory (DFT) implemented in the Vienna Ab-initio Package (VASP) 1,2 is employed to compile a reproducible and high-fidelity adsorption energy database to lend insights into searching and designing for corrosion resistant alloys (CRAs) on the atomic scale 3–6 . The current compilation and theory development begin with the high entropy alloy (HEA). Since the independent investigation of HEA by Yeh 7 and Cantor 8 , this class of alloy has shown a range of desirable features, such as good mechanical properties, phase stability at high temperature, and excellent corrosion resistance 7,9,10 . For these reasons, HEA has drawn attentions as possible candidate to supersede stainless steel for naval applications. One of the outstanding challenges to investigate HEA at the atomic scale, however, is the manifestation of randomness in the individual atoms that occupy the lattice sites. Two popular schools of theories have emerged over the years to tackle this issue. One is to overlay the potential fields of constituent atoms on top of the same lattice site, thereby ensuring “true” randomness 11 . The other is to score correlation function between first, second, third and so on nearest neighbor atoms with an Ising model approach to explicitly represent atoms within reasonable number for DFT computation 12 . Upon surveying the literature, both theories have been employed to mainly investigate the mechanical behavior of HEA 13,14 , while comparatively less has been adapted to study the corrosion resistant properties 15 . Herein, we propose a local bonding model to aid high throughput calculations that is necessary for both establishing a database and the subsequent screening of beneficial dopant elements in the design of CRAs. Our local bonding model is derived from the observation that the outer most layer atoms that come into contact with environment contribute the most to the computed adsorption energies. For HEA that has face-center-cubic (fcc) lattice, the local bonding model reduces to account for the most frequently occurring low-index fcc (111) surface, and the adsorption position on the three-fold fcc site. We will show that within this approach, the total number of DFT calculations become much more manageable and tractable. Furthermore, we expand upon the previously established concepts of aqueous species surface coverage 16 and chloride susceptibility index 17 , and include the alloy surface affinity for hydron and oxygen atoms. Altogether, we believe that the surface competition amongst chloride, hydrogen, and oxygen species can lend useful insights into re-passivation potential framework 18–22 for the CRAs of interest by establishing an unforeseen correlation. Reference G. Kresse and J. 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Zhang, Eds., High-Entropy Alloys: Fundamentals and Applications , Springer, (2016). T. Li et al., Electrochim. Acta , 306 , 71–84 (2019) https://doi.org/10.1016/j.electacta.2019.03.104. E. Materials, The EMTO-CPA Method , p. 83–94, (2007). S. Wei, L. G. Ferreira, J. E. Bernard, and A. Zunger, 42 (1990). C. Niu, C. R. LaRosa, J. Miao, M. J. Mills, and M. Ghazisaeidi, Nat. Commun. , 9 , 1–9 (2018) http://dx.doi.org/10.1038/s41467-018-03846-0. C. Niu, A. J. Zaddach, C. C. Koch, and D. L. Irving, J. Alloys Compd. , 672 , 510–520 (2016) http://dx.doi.org/10.1016/j.jallcom.2016.02.108. A. J. Samin and C. D. Taylor, Corros. Sci. , 134 , 103–111 (2018) https://doi.org/10.1016/j.corsci.2018.02.017. C. D. Taylor, S. Li, and A. J. Samin, Electrochim. Acta , 269 , 93–101 (2018) https://doi.org/10.1016/j.electacta.2018.02.150. H. Ke, T. Li, P. Lu, G. S. Frankel, and C. D. Taylor, SSRN Electron. J. (2020). G. S. Frankel, T. Li, and J. R. Scully, J. Electrochem. Soc. , 164 , C180–C181 (2017) http://jes.ecsdl.org/lookup/doi/10.1149/2.1381704jes. T. Li, J. R. Scully, and G. S. Frankel, J. Electrochem. Soc. , 165 , C484–C491 (2018). T. Li, J. R. Scully, and G. S. Frankel, J. Electrochem. Soc. , 165 , C762–C770 (2018). T. Li, J. R. Scully, and G. S. Frankel, J. Electrochem. Soc. , 166 , C115–C124 (2019). T. Li, J. R. Scully, and G. S. Frankel, J. Electrochem. Soc. , 166 , C3341–C3354 (2019).

Abstract: In this poster presentation, first principle density functional theory (DFT) implemented in the Vienna Ab-initio Simulation Package (VASP) is coupled with Chlorine Susceptibility Index (CSI) to guide the design of high entropy alloys (HEA) for materials employed in marine environment. On the atomic scale, elements within HEAs are randomly distributed throughout the alloy. This disordered crystalline state renders the investigation of all possible combinations impossible for DFT calculations. The CSI methodology developed by Dr. Huibin Ke in the Taylor group can be applied here to circumvent this issue [1]. The first successful CSI model for alloy systems was derived based on the special quasi-random structure approach[2] utilized for the study of Ni-Cr 22 alloy[3] and uses the first-principles thermodynamics approximation that allows the prediction of preferred chemisorption states in mixed media as a function of pH, electrochemical potential and chloride concentration[4] . Herein, we apply this method in search for combinations of elements that can provide the best corrosion resistance, under constraints of satisfying the high entropy alloy predictors of configurational entropy, valence electron concentration, atomic size difference[5] as well as cost efficiency (cost should be on par with Stainless Steel 304). Performance predictions will be compared with a parallel experimental program involving alloy synthesis, structural characterization and electrochemical characterization of the corrosion performance [6] . Reference: [1] H. Ke and C.D. Taylor, Chloride Susceptibility Index (CSI): An ab initio based corrosion resistance indicator, Research in Progress, NACE (2019), Nashville, TN [2] S. Wei, L.G. Ferreira, J.E. Bernard, A. Zunger, Electronic properties of random alloys: Special quasirandom structures, 42 (1990). [3] A.J. Samin, C.D. Taylor, First-principles investigation of surface properties and adsorption of oxygen on Ni-22Cr and the role of molybdenum, Corros. Sci. 134 (2018) 103–111. doi:10.1016/j.corsci.2018.02.017. [4] C.D. Taylor, S. Li, A. Samin, S. Li, A. Samin, Oxidation versus salt-film formation: Competitive adsorption on a series of metals from first-principles, Electrochim. Acta. (2018). doi:10.1016/j.electacta.2018.02.150.This. [5] M.C. Gao, J.-W. Yeh, P.K. Liaw, Y. Zhang, eds., High-Entropy Alloys: Fundamentals and Applications, Springer, 2016. doi:10.1007/978-3-319-27013-5_12. [6] A. Panindre, G.B. Viswanathan, S. Li, C. D. Taylor, G.S. Frankel, The effect of intermediate temperature anneal on the corrosion properties of a High Entropy Alloy, NACE Conference 2019, Nashville, TN, USA.

Abstract: 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 Al 7 FeCu 2 , 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 Mg 2 Si and MgZn 2 , 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: [1] C.D. Taylor, S. Li, A. Samin, S. Li, A. Samin, Oxidation versus salt-film formation: Competitive adsorption on a series of metals from first-principles, Electrochim. Acta. (2018). doi:10.1016/j.electacta.2018.02.150.This. [2] J.K. Nørskov, J. Rossmeisl, A. Logadottir, L. Lindqvist, J.R. Kitchin, T. Bligaard, H. Jónsson, Origin of the overpotential for oxygen reduction at a fuel-cell cathode, J. Phys. Chem. B. 108 (2004) 17886–17892. doi:10.1021/jp047349j. [3] H. Ma, X.Q. Chen, R. Li, S. Wang, J. Dong, W. Ke, First-principles modeling of anisotropic anodic dissolution of metals and alloys in corrosive environments, Acta Mater. 130 (2017) 137–146. doi:10.1016/j.actamat.2017.03.027. [4] H.A. Hansen, V. Viswanathan, J.K. Nørskov, Unifying Kinetic and Thermodynamic Anal ysis of 2 e – and 4 e – Reduction of Oxygen on Metal Surfaces, J. Phys. Chem. C. 118 (2014) 6706–6718. doi:10.1021/jp4100608. [5] N. Birbilis, R.G. Buchheit, Electrochemical Characteristics of Intermetallic Phases in Aluminum Alloys, J. Electrochem. Soc. 152 (2005) B140. doi:10.1149/1.1869984. [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.

Abstract: Corrosion is an electrochemical phenomenon. It can occur via different modes of attack, each having its own mechanisms, and therefore there are multiple metrics for evaluating corrosion resistance. In corrosion resistant alloys (CRAs), the rate of localized corrosion can exceed that of uniform corrosion by orders of magnitude. Therefore, instead of uniform corrosion rate, more complex electrochemical parameters are required to capture the salient features of corrosion phenomena. Here, we collect a database with an emphasis on metrics related to localized corrosion. The six sections of the database include data on various metal alloys with measurements of (1) pitting potential, E pit , (2) repassivation potential, E rp , (3) crevice corrosion potential, E crev , (4) pitting temperature, T pit , (5) crevice corrosion temperature, T crev , and (6) corrosion potential, E corr , corrosion current density, i corr , passivation current density, i pass , and corrosion rate. The experimental data were collected from 85 publications and include Al- and Fe-based alloys, high entropy alloys (HEAs), and a Ni-Cr-Mo ternary system. This dataset could be used in the design of highly corrosion resistant alloys.