A modified analytic embedded atom method (MAEAM) potential is constructed for fcc δ-Pu.Molecular dynamics (MD) simulations with the potential are performed to investigate the interactions between two symmetrical tilt grain boundaries (GBs) and point defects such as He atom,vacancy and self-interstitial atom (SIA) in Pu.The calculated results show that point defect formation energies are on average lower than those in the lattice but variations from site to site along the GBs are very remarkable.Both substitutional and interstitial He atoms are trapped at GBs.Interstitial He atom is more strongly bound at the GB core than the substitutional He atom.The binding energy of SIA at GB core is higher than those of He atom and vacancy.GB core can bind many He atoms and SIAs due mainly to the fact that it contains many vacancies.Compared with He atom and SIA,the vacancy far from GB core is difficult to diffuse into the core.The GBs can act as sinks and sources of He atoms and SIAs,which may be a reason for the swelling of Pu after a period of self-irradiation because of the higher concentration of vacancy in the bulk.
Due to a radioactive decay Pu is vulnerable to aging.The behavior of He in Pu is the foundation for understanding Pu self-radiation damage aging.Molecular dynamics technique is performed to investigate the behavior of defects,the interaction between He and defects,the processes of initial nucleation and growth of He bubble and the dependence of He bubble on the macroscopical properties of Pu.Modified embedded atom method,Morse pair potential and the Lennard-Jones pair potential are used for describing the interactions of Pu-Pu,Pu-He and He-He,respectively.The main calculated results show that He atoms can combine with vacancies to form Hevacancy cluster(i.e.,the precursor of He bubble)during the process of self-radiation as a result of high binding energy of an interstitial He atom to vacancy;He bubble’s growth can be dominated by the mechanism of punching out of dislocation loop;the swelling induced by He bubble is very small;grain boundaries give rise to an energetically more favorable zone for the interstitial He atom and self-interstitial atom accumulation than for vacancy accumulation;the process of He release can be identified as the formation of release channel induced by the cracking of He bubble and surface structure.
Bingyun AoPiheng ChenPeng ShiXiaolin WangWangyu HuLiang Wang
钚因放射性衰变而出现自辐照老化效应。钚中氦行为是理解钚自辐照老化效应的一个基础和前提。运用分子动力学模拟技术,计算研究了钚中缺陷行为、氦与缺陷的相互作用、氦泡的初始形核过程、氦泡的长大过程以及氦泡对钚材料宏观性能的影响等。其中,钚-钚、钚-氦和氦-氦相互作用势分别采用修正嵌入原子多体势(modified embedded atom method,MEAM)、Morse对势和Lennard-Jones对势。主要的计算结果表明,氦原子与空位的结合能较大,在钚的自辐照过程中,两者易于结合并形成氦-空位团簇,成为氦泡的前驱体;氦泡可通过冲出位错环的机制而长大;氦泡的压力在GPa量级,且氦泡引起的基体膨胀很小。
温度对bcc铁中的He行为有重要的影响,基于bcc晶格的晶格动力学蒙特卡罗(Lattice Kinetic Monte Carlo,LKMC)方法,模拟研究了298—1298K范围内温度对bcc铁中He行为的影响.结果表明:温度对bcc铁中He行为的影响可以分为4个阶段:(1)298—598K,(2)598—798K,(3)798—998K,(4)998—1298K.第一阶段随着温度的增加,晶粒内He原子浓度略有降低,但He泡中平均He原子个数迅速增加;第二阶段随着温度的增加,晶粒内的He原子浓度迅速降低,但He泡中平均He原子个数几乎不变;第三阶段随着温度的增加,晶粒内的He原子浓度和He泡中平均He原子个数均迅速减少;第四阶段随着温度的增加,晶粒内He原子浓度以及He泡中平均He原子个数均有所增加,到1298K时,晶粒内He原子浓度与室温时相近,几乎没有He原子从铁晶粒内逃逸出.模拟结果与文献正电子湮灭实验结果有很好的吻合.
