First-principles study of chromium diffusion in the ferritic Fe-Cr alloy

Ferritic Fe-Cr alloy is an important interconnect material for solid oxide fuel cell (SOFC) stacking. The Cr2O3 scale growth and Cr-induced cathode poisoning both related to the Cr diffusion have become the main concerns affecting the efficiency and life of the interconnect. In this study, a systematic theoretical study on the point defects and Cr diffusion process in the ferritic Fe-Cr alloy is performed by first-principles calculations. The different crystal models with vacancy or impurity Cr atoms are set up and optimized. The formation energies of two types of Fe vacancy and one type of Cr vacancy are obtained and compared. The adsorption of an impurity Cr atom in the Fe-Cr alloy is investigated and one type of stable tetrahedral interstitial and two types of metastable octahedral interstitials are found. Different diffusion pathways are explored including the vacancy diffusion and the interstitial Cr atom diffusion in the pure Fe layer and in the Fe-Cr mixed layer of the crystal, respectively. It is found that the interstitial Cr atom is easier to diffuse in the pure Fe layer in the studied Fe-Cr alloy. The activation energy and the diffusion coefficient of each diffusion pathway is obtained and the magnitude of Cr diffusion coefficient mainly varies from 10(-15) to 10(-12) m(2)/s under the realistic SOFC working temperature of 600 degrees C-800 degrees C. Our results provide a profound understanding of the microscopic diffusion mechanism of Cr atom in the ferritic Fe-Cr alloy, which could give theoretical guidance for the inhibition of Cr poisoning in the application of SOFC interconnect.