Evaluation of grain boundary segregation based on atomistic/electronic nonempirical analysis

用Bragg-Williams近似结合第一性原理密度泛函理论计算了杂质的偏析。考虑了反应堆压力容器中各元素的偏析倾向，并用平均场近似估计了-Fe与各杂质元素的相互作用特征。随后选择稳定的N原子杂质团簇来评价团簇自由能的变化。这些计算表明，嵌入在-Fe中的铜和锰杂质在偏析状态下更稳定。相反，Nb和Ta在分离溶质状态下是稳定的。目前的估计为偏析特征提供了可靠的建议。

The segregation of impurities were investigated by Bragg-Williams approximation combined with first principle density functional theory calculations. The segregation tendencies of various elements observed in reactor pressure vessels were considered and the interaction characteristics between □-Fe and each impurity element were estimated by mean field approximation. Stable N-atom impurity clusters were subsequently chosen to evaluate the changes in free energy for clustering. These calculations show that Cu and Mn impurities embedded in □-Fe are more stable when they are in the segregated state. Conversely, Nb and Ta are stable in the separately solute state. The present estimates provide reliable suggestions for the segregation characteristics.