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

采用第一性原理密度泛函理论结合Bragg-Williams近似方法研究了杂质的分凝行为。考虑了在反应堆压力容器中观察到的各种元素的偏聚倾向，并利用平均场近似估计了□-Fe与各杂质元素之间的相互作用特性。随后选择稳定的N原子杂质团簇来评估团簇自由能的变化。这些计算表明，嵌入在□-Fe中的Cu和Mn杂质在处于偏聚状态时更稳定。相反，Nb和Ta在单独的溶质状态下是稳定的。目前的估计提供了可靠的建议的离析特征。

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.