First-principles study of corrosion behavior of iron-base alloys

Haitao Wang ^1,2*, Xiaoran Yin¹, En-Hou Han^1,2*

¹ CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

² Institute of Corrosion Science and Technology, Guangzhou 510530, China

EXTENDED ABSTRACT: Iron-based alloys have a wide range of applications for theirs good mechanical and processing performance, along with excellent oxidation and corrosion resistance. The corrosion resistance of alloys is highly dependent on the passive layer formed on the surface which protects the surface from ion transport, metal dissolution, and degradation. We systematically investigated the adsorption characteristics of environmental particles on the alloyed surface and theirs effects during the initial stage of oxidation, and explored the inherent mechanism of Cl-induced degradation in the oxide film. This provides a theory foundation for designing of corrosion-resistant alloys at the atomic scale. The results show that the presence of electrolyte has little effect on the surface energy and adsorption energy but apparently reduces the work function. Under a positive potential, the adsorption becomes stronger, whereas under a negative potential, the adsorption is weaker. The competition relationship between the O and Cl species can inhibit the oxidation process on the metal surface, which is consistent with the adsorption theory of passivation. The alloying elements such as Cr, Mn, W, Mo, and Nb would significantly decrease the negative effect caused by Cl. Those alloying elements are supposed to be the qualified candidates for corrosion-resistance elements under corrosive environment containing Cl. In the Fe2O3 and α-Cr2O3 oxide films, the formation of an O vacancy is found to be more favorable than the formation of a cation vacancy. Cl ingress into perfect surfaces via unoccupied octahedral interstitial site is endothermic, whereas Cl ingress into O vacancy is thermodynamically favorable with a negative value of insertion energy, which is consistent with the ion exchange model. This demonstrates that Cl can transport across O vacancy. The diffusion barrier is the highest in α-Cr2O3, followed by α-Fe2O3, and is the lowest at the interface region. The interface offers a favorable channel for Cl ion and O vacancy diffusion, which can lead to accumulation of Cl at the interface and finally result in the local breakdown.