Theoretical Prediction of Grain Boundary Segregation Using Nano-Polycrystalline Grain Boundary Model

Abstract

The importance of controlling grain boundary (GB) segregation is increasing, especially with the strengthening of steel nowadays. In this study, a theoretical prediction method for the amount of GB segregation for a solute element in polycrystals is established. This prediction method entails the development of a nano-polycrystalline GB model for simulating GBs in polycrystals, and the segregation energy of a solute element is comprehensively calculated for all atomic sites constituting the GB model by using an interatomic potential. From the obtained segregation energies, the segregation amount of the solute element at each atomic site is determined. Subsequently, each atomic site is classified based on its distance from the GB center and averaged to determine the segregation profile of the solute element for that distance from the GB center. By applying this method to the GB segregation of P in bcc-Fe and comparing the results with experimental findings, it is determined that this prediction method can deliver excellent prediction accuracies.

Application of Grain Boundary Segregation Prediction Using a Nano-Polycrystalline Grain Boundary Model to Transition Metal Solute Elements: Prediction of Grain Boundary Segregation of Mn and Cr in bcc-Fe Polycrystals

“…5 for all GBs. These results are similar to the behavior of P segregation in the nanopolycrystalline GB model, 29) which suggests that the nano-polycrystalline GB model used in this study contained a sufficient number of GBs to obtain the average amount of GB segregation of Cr and Mn in polycrystals. The average amounts of segregation in the polycrystal obtained as the average of the segregation amount at each GB were 1.11 at% and 3.11 at% for Cr and Mn, respectively.…”

“…For a more detailed discussion of the construction and validity of the prediction method, please refer to our previous report. 29) 2.1 Method for prediction of segregation amount and segregation energy in polycrystalline GBs using a nano-polycrystalline GB model Experimentally, the amount of GB segregation in a polycrystal is calculated as the average of the segregation amounts at several dozen different GBs, and the segregation energy in the polycrystal is determined from the amount of GB segregation. 32) When measuring the amount of segregation at each GB, the distance from the GB center to be measured depends on the analysis method.…”

“…The calculation conditions described below are the same as those used in the analysis of P segregation in bcc-Fe polycrystals, and they are known to predict well at least the amount of P GB segregation. 29) The Voronoi tessellation 34,35) was used to create the initial structure of the nano-polycrystalline GB model. First, we randomly place a number of points that form the source of the grains in the calculation cell.…”

“…To address this issue, we proposed a prediction method for GB segregation using a nano-polycrystalline GB model to improve the prediction accuracy of the amount of GB segregation in polycrystals. 29,30) In this prediction method, focusing on the fact that the atomic structure of GBs is almost independent of grain size, 31) GBs of polycrystals with grain sizes on the order of micrometers are modeled as GBs of nano-polycrystals, for which structural relaxation calculations by molecular dynamics calculations are possible. For this GB model, the segregation energy of a solute element is calculated comprehensively for all atomic sites constituting the GB model using an interatomic potential.…”

“…The developed prediction method was applied to the GB segregation of P in bcc-Fe polycrystals, and it was shown that the amount of GB segregation corresponding to the measurement region obtained by the prediction reproduced the experimental results well. 29) However, it is unclear whether the prediction method described above is valid for solute elements other than P. For example, many alloying elements are transition metal alloying elements, and it is necessary to investigate whether the experimental results can be well reproduced for these elements. The bonding between Fe and the transition metal solute elements in bcc-Fe is primarily metallic bonding between d-orbital electrons.…”