Kavli Institute of Nanoscience, Delft University of Technology, 2628, CJ, Delft, The Netherlands.
Center for High Resolution Electron Microscopy, College of Materials Science and Engineering, Hunan University, 410082, Changsha, China.
Sci Rep. 2017 May 19;7(1):2184. doi: 10.1038/s41598-017-02081-9.
Age-hardening in Al alloys has been used for over a century to improve its mechanical properties. However, the lack of direct observation limits our understanding of the dynamic nature of the evolution of nanoprecipitates during age-hardening. Using in-situ (scanning) transmission electron microscopy (S/TEM) while heating an Al-Cu alloy, we were able to follow the growth of individual nanoprecipitates at atomic scale. The heat treatments carried out at 140, 160, 180 and 200 °C reveal a temperature dependence on the kinetics of precipitation and three kinds of interactions of nano-precipitates. These are precipitate-matrix, precipitate-dislocation, and precipitate-precipitate interactions. The diffusion of Cu and Al during these interactions, results in diffusion-controlled individual precipitate growth, an accelerated growth when interactions with dislocations occur and a size dependent precipitate-precipitate interaction: growth and shrinkage. Precipitates can grow and shrink at opposite ends at the same time resulting in an effective displacement. Furthermore, the evolution of the crystal structure within an individual nanoprecipiate, specifically the mechanism of formation of the strengthening phase, θ', during heat-treatment is elucidated by following the same precipitate through its intermediate stages for the first time using in-situ S/TEM studies.
铝合金属时效硬化的应用已经超过一个世纪，旨在提高其机械性能。然而，由于缺乏直接观察，我们对时效硬化过程中纳米沉淀物动态演变的理解仍然有限。本研究通过原位（扫描）透射电子显微镜（S/TEM）加热 Al-Cu 合金，能够在原子尺度上跟踪单个纳米沉淀物的生长。在 140、160、180 和 200°C 进行的热处理揭示了沉淀动力学与纳米沉淀物的三种相互作用（沉淀-基体、沉淀-位错和沉淀-沉淀相互作用）之间的温度依赖性。在这些相互作用中，Cu 和 Al 的扩散导致了扩散控制的单个沉淀物生长，当与位错发生相互作用时会加速生长，并且沉淀-沉淀相互作用具有尺寸依赖性：生长和收缩。沉淀物可以在同一时间的相反两端生长和收缩，从而导致有效位移。此外，通过首次使用原位 S/TEM 研究，跟踪同一沉淀物的中间阶段，阐明了单个纳米沉淀物内晶体结构的演变，特别是强化相 θ'的形成机制。
