辐照镍中自间隙原子团簇的形貌与动力学

中文摘要 AI 辅助

自间隙原子（SIA）团簇是面心立方（FCC）金属中辐射损伤演化的关键早期步骤，决定缺陷输运、复合以及辐照合金的长期微观结构响应。我们结合分子动力学（MD）模拟与高速（>1000帧/秒）原位透射电子显微镜（TEM），研究FCC镍中SIA团簇的结构、能量学及迁移动力学。MD模拟显示，间隙原子最初形成无序哑铃型团簇，随后演变为不可动的弗兰克（Frank）环或可动的完整（棱柱）环；后者随迁移率增加逐步重组为致密有序构型。对宽尺寸范围内两类环的直接构建（经MD弛豫结构验证）表明，当SIA数量N≥14时，完整环在热力学上比弗兰克环更具优势，且能量优势随团簇尺寸增大而提升；不过，显著的动力学势垒使弗兰克环能作为亚稳态缺陷持续存在。针对N=16至400的完整环，计算得到的扩散系数显示其迁移势垒几乎与尺寸无关，约为0.02 eV，而扩散前置因子近似按N^(-0.54)减小。轨迹分析揭示了非刚性的逐行接力机制，其中参与原子数随环尺寸系统增加，这解释了大部分观测到的前置因子标度关系。亚毫秒级原位TEM观测显示，环的运动呈间歇性，其速度高于此前观测值，但仍比MD预测的本征迁移率低数个数量级，表明环通过由可动态与钉扎态构成的异性能量景观发生迁移。

英文摘要

Self-interstitial atom (SIA) clustering is a key early step in radiation damage evolution in face-centered cubic (FCC) metals, governing defect transport, recombination, and the long-term microstructural response of irradiated alloys. We combine molecular dynamics (MD) simulations and high-speed (>1000 frames/s) in situ transmission electron microscopy (TEM) to investigate the structure, energetics, and migration dynamics of SIA clusters in FCC Ni. MD simulations show that interstitials initially form disordered dumbbell clusters that evolve into either sessile Frank loops or glissile perfect (prismatic) loops; the latter progressively reorganize into compact ordered configurations with increasing mobility. Direct construction of both loop types over a wide size range, validated against MD-relaxed structures, shows that perfect loops are thermodynamically favored over Frank loops for cluster sizes N greater than or equal to 14, where N is the number of SIAs, with the energetic advantage increasing with cluster size. Nevertheless, substantial kinetic barriers allow Frank loops to persist as metastable defects. For perfect loops, diffusion coefficients computed over N = 16 to 400 reveal a nearly size-independent migration barrier of approximately 0.02 eV, while the diffusion prefactor decreases approximately as N^(-0.54). Trajectory analysis reveals a non-rigid, row-wise relay mechanism in which the number of participating atoms increases systematically with loop size, accounting for much of the observed prefactor scaling. Sub-millisecond in situ TEM observations reveal intermittent loop motion at velocities higher than previously observed but still several orders of magnitude below the intrinsic mobilities predicted by MD, indicating migration through a heterogeneous energy landscape of mobile and pinned states.

发表机构

• University of Wisconsin-Madison（威斯康星大学麦迪逊分校）
• University of Michigan（密歇根大学）

机构由 AI 辅助整理，请以论文原文为准。