Irradiation induced significant volume fractions of Mn-Ni-Si clusters have been characterized as severe cause for the matrix embrittlement in low-Cu reactor pressure vessel steels (RPV) at high flux. The formation mechanism of these clusters is still unclear, especially when the RPV does not contain Cu. In this work, we perform density functional theory (DFT) calculations to examine the mechanism of the role of specific element species in the local stability of clusters in Fe-Mn-Ni-Si system. The binding energy of different species or configurations for quartets including Mn, Ni, Si, vacancies, and interstitial atoms is presented. Based on the DFT data, we found that point defects are more likely to promote cluster formation, and when Mn is present near the dumbbell interstitials, is favorable for formation of the cluster. Si also plays an important role by forming stable covalent bonds at 1nn to other solutes, but Si atoms cannot be close to each other because this would interfere with the magnetic properties of the surrounding Fe atoms to the extent of reducing the stability of the clusters. These results are helpful for a better understanding of the cluster formation mechanism and can provide fundamental parameters for the solute-cluster evolution with larger scale simulations.

辐照诱导显着体积分数的 Mn-Ni-Si 簇已被表征为高通量下低铜反应堆压力容器钢 (RPV) 中基体脆化的严重原因。这些团簇的形成机制尚不清楚，尤其是当 RPV 不含 Cu 时。在这项工作中，我们进行了密度泛函理论 (DFT) 计算，以研究特定元素种类在 Fe-Mn-Ni-Si 系统中簇的局部稳定性中的作用机制。介绍了四重体（包括 Mn、Ni、Si、空位和间隙原子）的不同种类或构型的结合能。基于 DFT 数据，我们发现点缺陷更有可能促进团簇的形成，当哑铃间隙附近存在 Mn 时，有利于团簇的形成。Si 也通过在 1nn 处与其他溶质形成稳定的共价键而发挥重要作用，但 Si 原子不能彼此靠近，因为这会干扰周围 Fe 原子的磁性，从而降低团簇的稳定性。这些结果有助于更好地理解团簇形成机制，并可以通过更大规模的模拟为溶质团簇演化提供基本参数。