Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.
Nat Commun. 2013;4:2288. doi: 10.1038/ncomms3288.
The formation of voids in an irradiated material significantly degrades its physical and mechanical properties. Void nucleation and growth involve discrete atomic-scale processes that, unfortunately, are not yet well understood due to the lack of direct experimental examination. Here we report an in-situ atomic-scale observation of the nucleation and growth of voids in hexagonal close-packed magnesium under electron irradiation. The voids are found to first grow into a plate-like shape, followed by a gradual transition to a nearly equiaxial geometry. Using atomistic simulations, we show that the initial growth in length is controlled by slow nucleation kinetics of vacancy layers on basal facets and anisotropic vacancy diffusivity. The subsequent thickness growth is driven by thermodynamics to reduce surface energy. These experiments represent unprecedented resolution and characterization of void nucleation and growth under irradiation, and might help with understanding the irradiation damage of other hexagonal close-packed materials.
辐照材料中空隙的形成会显著降低其物理和机械性能。空隙的成核和生长涉及离散的原子尺度过程，但由于缺乏直接的实验研究，这些过程目前还没有得到很好的理解。在这里，我们报告了在电子辐照下六方密堆积镁中空隙成核和生长的原子尺度原位观察。结果表明，空隙首先生长成板状，然后逐渐过渡到近等轴几何形状。通过原子模拟，我们表明初始长度的增长受到基底面上空位层的缓慢成核动力学和各向异性空位扩散的控制。随后的厚度增长则是由热力学驱动，以降低表面能。这些实验代表了在辐照下对空隙成核和生长的前所未有的分辨率和特性描述，有助于理解其他六方密堆积材料的辐照损伤。
