纳米结构铁素体合金中氦捕获的第一性原理研究

First principles study of helium trapping in nano-structured ferritic alloys

基于第一性原理计算研究纳米结构铁素体合金(NFAs)对中子辐照引发的氦的选择性捕获能力。结果表明与铁基体中的空位相比,氦更容易被NFAs中Y_2Ti_2O_7的八面体间隙和Y_2TiO_5沿b轴方向的中空通道捕获;被氧化物捕获的氦相互间存在排斥作用,说明氦在NFAs中的分散度将在很大程度上取决于氧化物的析出分数和弥散度;通过计算界面相图推断,铁素体/Y_2Ti_2O_7界面应为富Y/Ti型,与实验观测到的Y_2Ti_2O_7析出相的非化学计量比特性吻合;氦对Fe/Y_2Ti_2O_7界面有较强的偏聚倾向,且可能对氧化物颗粒尺寸敏感。较大尺度的Y_2Ti_2O_7能够将氦捕获在界面和体内,而低纳米尺度的Y_2Ti_2O_7更倾向于将氦捕获在界面。

First principles was studied for assessing the relative stabilities of transmutant helium trapping in Y2Ti2O7,Y2TiO5 and the ferrite matrix in nano-structured ferritic alloys（NFAs）.The results suggest that,helium in NFAs prefers to occupy individual octa-interstitial sites of Y2Ti2O7 and the open channels along the b axis of Y2TiO5.The helium self-interaction in Y2Ti2O7 is essentially repulsive,suggesting that the dispersion of helium in NFAs might,to a large extent,depend on the number and dispersion of Y2Ti2O7 in the iron matrix.The calculated interface phase diagram predicts the ferritic/Y2Ti2O7 interfaces in NFAs as Y/Ti-rich,in agreement with the experimentally observed non-stoichiometric nature of Y2Ti2O7 precipitates in NFAs.Segregation tendency of helium to the ferritic/Y2Ti2O7interface can be sensitive to the size of Y2Ti2O7.