Fe-Cr合金气泡演化动力学的相场法模拟

Phase Field Simulation of Bubble Evolution Dynamics in Fe-Cr Alloys

Fe-Cr系合金是反应堆堆芯关键部件用材,辐照缺陷和不溶解嬗变He气等簇聚形成气泡,是该类材料不可逆辐照肿胀和脆性根源。本工作利用介观尺度的相场模型耦合辐照、温度和弹性应力场,研究了合金成分和位错应力场对Fe-Cr合金气泡演化的影响。结果表明,当体系中的气体和空位过饱和时,气体原子优先在空位团簇和位错等异质形核位点处聚集,并吸收空位和气体原子而长大。当气泡长大到一定尺寸时,其气体含量不再增加,主要通过吸收空位来进一步生长,此时气泡内的压力低于相同尺寸气泡的平衡压力,气泡内的空位饱和度较高,气泡主要表现为空洞的性质。Cr元素的加入会降低空位和气体原子的扩散速率,随着合金中Cr含量的增加,气泡的形核孕期延长,延缓气泡的形核和长大。位错应力场通过与空位和气体原子的相互作用,促进气泡优先在刃型位错的拉应力区形核,加速了气泡局域择优形核长大。本工作阐明了影响气泡生长的关键动力学因素,如微结构、扩散等,为辐照气泡组织调控和稳定力学性能提供了重要依据。

Fe-Cr alloys are essential materials for core reactor components.The long-term in-core service of these components under intense radiation,thermal,and stress coupling conditions may potentially expedite the degradation of their mechanical properties.Radiation defects and insoluble helium gas molecules are generally trapped in voids or grain boundaries,forming intra-or intergranular fission gas bubbles.These bubbles cause irreversible radiation volumetric swelling and brittleness.However,a comprehensive understanding of the bubble formation process,particularly the effects of Cr content and dislocation stress field on the formation,remains unclear.As a mesoscale simulation approach,the phase field model coupled with irradiation,temperature,and elastic stress has been employed to study bubble evolution influenced by alloy composition and dislocation configuration.This approach offers advantages when addressing bubble-formation-related issues on different spatial and temporal scales.In this work,the phase field method is employed to investigate bubble growth kinetics and the effects of Cr content and dislocation stress field on bubble formation and evolution in Fe-Cr alloy under radiation.The simulations reveal that in an oversaturated gas and vacancy system,gas atoms tend to cluster at heterogeneous nucleation sites,such as vacancy clusters and dislocations,and grow by absorbing vacancy and gas atoms.The bubbles maintain a constant gas concentration up to a certain size as they continue to grow by absorbing vacancies.However,when the vacancy saturation is high,a bubble will behave as a void if its outward pressure is lower than the equilibrium pressure of a bubble of the same size.Cr additives reduce the diffusion rate of gas atoms and vacancies,extending the nucleation period of bubbles and decelerating their growth and coarsening.Dislocations cause vacancies and gaseous atoms to aggregate in the tension stress regions of the edge dislocation,enhancing the bubbles preferential heterogeneous nucleation in that area.This work discusses key kinetic elements affecting bubble evolution,including intrinsic microstructures and diffusivity.Further,it provides inspiration for future material designs for improving irradiation resistance and long-term service stability.