Influence of Si, Mn, Cr, and C Doping Impurities on Grain Boundary Segregation of Phosphorus in α-Iron

This paper first uses ab initio calculations for a systematic study of an influence of Cr, Mn, C, and P alloying elements on the grain boundary segregation of phosphorus in ferromagnetic α-Fe and its dependence on the nature of grain boundaries. Segregation energies of each element and site are fully calculated for two special grain boundaries of the types Σ3(111) and Σ5(310). We study the effect of grain boundary type on the segregation process of alloying elements. The estimate of effective segregation energy for each model of grain boundaries from the obtained segregation energies and analysis of the alloying element distribution at various boundary points are carried out. The paper shows that the Voronoi volume of a Fe site at the segregation point determines the segregation energy of the elements under study. The segregation energies of various pairs of impurities on the boundary are calculated. The effect of substitutional impurities on the change in the segregation energy of phosphorous atoms at the interstitial and substitutional sites and the effect of the phosphorous atom on the change in the impurity segregation energy at various boundary points are studied. The results obtained in this study correspond closely to the available experimental data and provide important base data for the design of high strength steel materials, and are useful for understanding the effect of alloying elements on bcc Fe.