First-principles analysis of the grain boundary segregation of transition metal alloying elements in γFe

Abstract

In this study, first-principles calculations were carried out for the first time to systematically investigate the grain boundary segregation of transition metal alloying elements (Ti, V, Cr, Mn, Co, Ni, Cu, Nb, and Mo) in paramagnetic γFe and its dependence on the grain boundary character. The segregation energies of each element and site were comprehensively calculated for nine [001] symmetric tilt grain boundary models with Σ values from 5 to 41; the paramagnetic state was simulated by the antiferromagnetic double-layer (AFMD). By calculating the effective segregation energy for each grain boundary model from the obtained segregation energies, the grain boundary segregation behavior for each alloying element and its dependence on the grain boundary character were investigated. The segregation energy of transition metal elements is dominated by the Voronoi volume of Fe at the segregation site and arises from the elastic energy derived from the difference in atomic radii between the host and solute metals. Ti, Cu, Nb, and Mo have negative effective segregation energies (indicating a tendency toward segregation) at all investigated grain boundaries, and the absolute values of the effective segregation energy increase in the order of Cu < Mo < Ti < Nb in all of the grain boundary models. In contrast, the sign of the effective segregation energies for V, Ni, and Co changes depending on the grain boundary, and the effective segregation energies for Cr and Mn are positive at all grain boundaries. These results corresponded well with the experimental results. The results obtained in this study provide important basic data for the material design of high-strength steels and are useful for understanding the effects of alloying elements in γFe.