反应堆压力容器钢中溶质元素空位型扩散机理研究

Vacancy-mediated Diffusion Mechanism of Solute Element in Reactor Pressure Vessel Steel

辐照或热老化导致元素偏析和沉淀析出是反应堆压力容器(reactor pressure vessel,RPV)钢性能退化的主要影响因素,点缺陷与合金/杂质元素结合与扩散是引起元素偏析和沉淀析出的主要原因。本文利用分子动力学方法研究了反应堆压力容器钢中几种主要合金/杂质元素(Cu、Ni、Mn、P)的空位型扩散机理。研究了空位与合金/杂质元素的结合性能;基于多频模型计算了合金/杂质元素的空位风参数和扩散系数。通过计算发现,Cu、P与第1近邻、第2近邻空位均具有较大的结合能,Ni与第2近邻空位具有较大的结合能;溶质元素的空位风均随着温度的升高而增大,表明在高温下合金/杂质元素均倾向通过与空位互换位置而扩散。

The diffusion of solutes in reactor pressure vessel （RPV） steel, accompanied with point defects, will result in the formation of precipitation and segregation on grain boundary, which will cause the hardening and embrittlement of materials. In order to deepiy understand the performance degradation of RPV steel, the knowledge on solute diffusion mechanism is required. The vacancy-mediated diffusion mechanism of major solutes in RPV steel was studied by molecular dynamics method. Firstly, solute-vacancy interactions were studied. Subsequently, based on multi-frequency model, the vacancy drag factor and diffusion coefficient were calculated. The results show that Cu and P have strong binding energies with vacancies both in the first nearest neighbor （Inn） and the second nearest neighbor （2nn）, and Ni has stronger binding energy with 2nn vacancy than 1nn vacancy. The vacancy drag factor increases with temperature, which means that solutes diffuse by exchanging with vacancy at high temperature.