In situ observations of nano precipitate growth
Dispersion strengthening is a common phenomenon used to enhance the strength of engineering materials. In commonly used structural alloys for automobile and aerospace applications like aluminum and nickel based alloys, this is achieved by the formation of precipitates upon heat-treatment, a process called precipitation hardening. The difference in the solid solubilities of alloying elements makes it possible to precipitate fine particles of a secondary phase by heat-treatment. This is called aging.
DENSsolutions’ single tilt (70 degrees) sample heating system (Wildfire S5) provides the opportunity to optimize this process by directly imaging the growth of nano precipitates during the heat treatment. Fig. 1 gives an example of the application of the system in the study of precipitate growth in Al2024-T3.
The Wildfire S5 can heat specimens from room temperature to 1300 °C in a (S)TEM. Its large tilt range of ±70° enables the acquisition of tomography tilt series of the growing precipitates. Depending on the recorded image intensities, it might be possible to reconstruct and visualize the three-dimensional density distribution of the sample. Fig. 2b shows a 3D network of nano-precipitates in Al2024-T3 reconstructed from a series of HAADF-STEM images.
Images from Sairam Malladi, National Center for HREM, TU Delft.