One of the key challenges in alloys development is the quest for a deeper understanding of fundamental processes happening on the micro- and nanoscale, triggered either by minuscule changes of composition or by different types of treatments.
During the last decade, high-resolution scanning transmission electron microscopy (HR-STEM) received significant improvements for high-speed chemical analysis based on advanced spectroscopic techniques like direct-electron-detection based electron energy-loss spectroscopy (EELS) and large efficiency energy dispersive x-ray spectroscopy. In addition, STEM also offers the possibility of in situ experiments (e.g. heating, biasing) for the microscopic insight into dynamic processes like precipitate growth, and 3D reconstruction techniques for obtaining the structure and composition in three dimensions. The overall combination of these methods makes HR-STEM an indispensable tool in modern alloy design.
In this study, we use atomic resolution imaging and powerful local chemical analysis to illustrate the structure, composition and evolution of precipitates in various aluminum alloys (e.g. AlCu4, AlSi10MnMg). We track temperature-triggered growth processes with nanoscale resolution during in situ heating experiments as well as capture and describe the changes of the system during different stages of precipitate formation using fast EELS techniques to examine the chemical composition.
HR-STEM is capable of providing detailed insight into various stages of the precipitation process that is crucial for the alloy's properties. This in-depth knowledge is essential for the material design procedure as it provides guidelines for optimization based not only on macroscopic characteristics, but also on the microstructural features that are the driving forces behind the materials properties.