Dr. Sairam K. Malladi

Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands. Authors | Sairam K. Malladi, Qiang Xu, Marijn A. van Huis, Frans D. Tichelaar, K. Joost Batenburg, Emrah Yücelen, Beata Dubiel, Aleksandra Czyrska-Filemonowicz, and Henny W. Zandbergen. EmailH.W.Zandbergen@tudelft.nl.

ApplicationReal-Time Atomic Scale Imaging of Nanostructural Evolution in Aluminum Alloys
AuthorsSairam K. Malladi, Qiang Xu, Marijn A. van Huis, Frans D. Tichelaar, K. Joost Batenburg, Emrah Yücelen, Beata Dubiel, Aleksandra Czyrska-Filemonowicz, and Henny W. Zandbergen.
JournalNano Lett., 2014, 14 (1), pp 384–389
SampleFIB lamella, Metal
TopicHeat Treatment, Aging, Precipitation
FieldMaterials Science, Micro Electronics
TechniquesHRTEM, EDX mapping
KeywordsIn situ (S)TEM; precipitation; aluminum alloys
PublicationFull Publication Here – DOI 10.1021/nl404565j

Real-Time Atomic Scale Imaging of Nanostructural Evolution in Aluminum Alloys

ABSTRACT: We present a new approach to study the three dimensional alloys during heat treatments such as commonly used for improving overall material properties. It relies on in situ heating in a high-resolution scanning transmission electron microscope (STEM). The approach is demonstrated using a commercial Al alloy AA2024 at 100−240 °C, showing in unparalleled detail where and how precipitates nucleate, grow, or dissolve. The observed size evolution of individual precipitates enables a separation between nucleation and growth phenomena, necessary for the development of refined growth models. We conclude that the in situ heating STEM approach opens a route to a much faster determination of the interplay between local compositions, heat treatments, microstructure, and mechanical properties of new alloys.

FIGURE ABOVE: STEM imaging and EDX maps obtained at each of the intermediate stages of heat-treatment. These maps are obtained with a frame size of 512×512 pixels2 and a frame time of 100 s, averaged over three frames. Notice the Cu redistribution associated with the precipitation at grain boundaries and precipitation in the matrix during the heat-treatment processes. The lath-like nanoprecipitates are enriched with Cu and Mg, suggesting S-phase-type compositions. Throughout the heat-treatment process, the Mn-rich precipitates remained as they are at room temperature.

DENSsolutions Comments:

Most commercial engineering alloys undergo heat treatments to change their intrinsic microstructural properties, such as elemental distribution and precipitate density, to enhance their extrinsic physical properties such as mechanical strength. Despite the key importance of these treatments, studies of the compositional and structural evolution of alloys undergoing heat treatments are fragmented and time consuming as they have been carried out on a set of different samples taken at intermediate stages, which are postmortem data that do not show the evolution of the same area. Achieving in situ TEM observation of heat treatment process at atomic scale enable a full understanding of the relation among process, structure and properties.

The DENSsolutions heating system provides the minimal specimen drift at elevated temperature, allowing a novel in situ method to investigate the aging hardening process that the structural and compositional evolution of alloys can be directly analyzed with time and temperature down to atomic scale.

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