辐照损伤对钨晶格热导率影响的分子动力学研究

Molecular dynamics study on the effect of radiation damage on the lattice thermal conductivity of tungsten

钨是最具应用前景的面向等离子体候选材料,但核聚变堆内强烈的辐照环境会使钨的近表面区域产生辐照损伤,进而影响其关键的导热性能.本文构建了包含辐照损伤相关缺陷的晶体钨模型,并采用非平衡分子动力学的方法定量研究了这些缺陷对钨导热性能的影响.结果表明,随中子辐射能量的增加,晶体内部留下的Frenkel缺陷数目增多进而导致钨的晶格热导率降低;间隙原子比空位更易于向晶界偏聚,且钨中的间隙钨原子与空位相比,使晶格热导率下降程度更大.纳米级氦气泡导致晶格热导率的显著降低,气孔率为2.1%时晶格热导率降至完美晶体的约25%.这些不同的缺陷造成不同程度的周围晶格扭曲,增加了声子散射几率,是导致晶格热导率下降的根源.

Tungsten(W) has been considered as candidate plasma facing material(PFM) in nuclear fusion reactor. However, the severe work environment will cause radiation damage of W, which will affect its thermal energy transport. We constructed the structural model of undamaged and damaged W, and used the non-equilibrium molecular dynamics(NEMD) simulations to quantitatively study the thermal conductivity of W. The results show a decrease in lattice thermal conductivity with the increase of neutron radiation energy. Interstitial atoms trend to segregate at grain boundary, and the interstitial W atoms have a greater effect on lattice thermal conductivity than vacancies. Nanoscale-sized He bubbles cause a significant decrease in the lattice thermal conductivity of W, which down to ~25% of its perfect crystal value when the porosity is 2.1%. These different defects cause different degrees of lattice deformation, which increase the phonon scattering and result in the decrease of lattice thermal conductivity.