Dislocation climb driven by lattice diffusion and core diffusion
Dislocation climb driven by lattice diffusion and core diffusion
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晶格扩散和核扩散驱动的位错攀爬
DOI：
10.1016/j.jmps.2023.105300
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发表时间：
2023
影响因子：
5.3
通讯作者：
Liu F
中科院分区：
文献类型：
--
作者：
Liu F
材料的扩散对位错运动有着至关重要的影响，特别是在高温下。通常认为，在单晶中，当温度高时，晶格扩散占主导地位，而在相对低的温度下，芯扩散占主导地位。由于芯和晶格扩散之间的耦合建模的复杂性，一个给定的物理问题往往被简化为两个极端，其中只考虑两个扩散制度之一。然而，在何种条件下，每个扩散机制是占主导地位的定量定义仍然缺乏。在目前的工作中，我们采用变分原理的微观结构演变的分析，我们展示了如何有限元（FE）为基础的分析可以从它，其中核心扩散和晶格扩散之间的竞争和协同作用，可以自然地考虑。位错攀移模型进一步发展，将有限元分析的节点为基础的三维位错动力学框架，它也考虑滑移和交叉滑移过程。基于所提出的方法，对不同条件下棱柱形位错环（PDL）的合并过程进行了系统的研究;结合由核心扩散和晶格扩散控制的圆形PDL运动的解析解，构建了扩散机制图，为确定给定位错环尺寸、间距和温度下的主导扩散机制提供了有益的指导。结果表明，在实际的环粗化过程中，核心扩散为局部原子重排提供了快速短路，因此当环尺寸或环之间的距离较小时，特别是在温度低于0. 5 Tm（Tm是给定材料的熔点）。然而，在高温下，当环之间的距离大或当环尺寸大时，晶格扩散变得更有效。目前的研究结果表明，同时考虑核心和晶格扩散对于定量了解与位错攀爬相关的物理过程（例如蠕变和辐照后退火）的微观结构演变是必要的。
Diffusion of material has a crucial influence on dislocation motion, particularly at elevated temperatures. It is generally believed that, in a single crystal, lattice diffusion prevails when the temperature is high and core diffusion dominates at relatively low temperatures. Due to the complexity of modeling the coupling between core and lattice diffusion, a given physical problem is often simplified into two extremes where only one of the two diffusion regimes is considered. However, a quantitative definition of the conditions under which each of the diffusion mechanisms is dominant is still lacking. In the present work, we employ a variational principle for the analysis of microstructure evolution; we demonstrated how finite element (FE) based analysis can be developed from it, in which the competition and synergy between core diffusion and lattice diffusion can be naturally taken into consideration. A dislocation climb model is further developed by incorporating the FE analysis into the nodal based three-dimensional dislocation dynamics framework, which also considers glide and cross-slip processes. A systematic study of the coalescence of prismatic dislocation loops (PDLs) at various conditions is conducted based on the proposed method; together with the analytical solutions of the motion of a circular PDL controlled by core and lattice diffusion, a diffusion mechanism map is constructed, which provides useful guidance on determining the dominant diffusion mechanism for given loop sizes, spacing, and temperature. The results show that, in a practical loop coarsening process, core diffusion provides a fast short circuit for local atomic rearrangement, so that it is dominant when loop size or the distance between loops is small, particularly at temperatures lower than 0. 5 T m (T m is the melting point of a given material). While, at high temperatures, when the distance between loops is large or when the loop size is large, lattice diffusion becomes more efficient. The present findings indicate that simultaneous consideration of both core and lattice diffusion is necessary to quantitatively understand the microstructure evolution for dislocation climb related physical processes, such as creep and post-irradiation annealing.