ABSTRACT

In the literature, the volume of a cluster (i.e. a fluctuation of the solid solution or a precipitate) is identified as the volume of a sample of the bulk precipitate phase containing the same number of solute atoms (i.e. of the same size). This approximation is suitable for macroscopic precipitates but is debatable for a rigorous description of microscopic clusters, especially during the nucleation and growth stages. To go beyond this simplification, this work focuses on the notion of ‘exclusion volume’, a volume which accounts for real cluster configurations in a given 3D lattice. The exclusion volume normalised by the cluster size is a complex function of the cluster size, which, like the cluster free energy, evolves during precipitation kinetics and converges toward an asymptote in the long-time limit. Furthermore, this asymptote exhibits a bifurcation which clearly separates fluctuations from precipitates, for a cluster size which is found equal to the minimum value of the critical size for nucleation. With the help of Atomistic Kinetic Monte Carlo (AKMC) simulations, it is shown that the evolution of cluster volume during precipitation can be accurately predicted.

摘要

在文献中，团簇的体积（即，固溶体或沉淀物的波动）被识别为包含相同数量的溶质原子（即，具有相同大小）的本体沉淀相的样品的体积。该近似值适用于宏观沉淀，但对于微观团簇的严格描述是有争议的，尤其是在成核和生长阶段。为了超越这种简化，本文将重点放在“排除体积”的概念上，该体积考虑了给定3D晶格中的实际群集配置。由团簇尺寸归一化的排阻体积是团簇尺寸的复杂函数，像团簇自由能一样，它在降水动力学过程中演化并在长期极限内收敛于渐近线。此外，该渐近线表现出分叉，该分叉清楚地将波动与沉淀物分离开，对于簇大小，该簇大小等于成核的临界大小的最小值。借助原子动力学蒙特卡洛（AKMC）模拟，表明可以准确预测降水过程中团簇体积的演变。