Small-angle scattering

Résumé

Small-angle scattering (SAS) is a scattering technique based on deflection of collimated radiation away from the straight trajectory after it interacts with structures that are much larger than the wavelength of the radiation. The deflection is small (0.1-10°) hence the name small-angle. SAS techniques can give information about the size, shape and orientation of structures in a sample. SAS is a powerful technique for investigating large-scale structures from 10 Å up to thousands and even several tens of thousands of angstroms. The most important feature of the SAS method is its potential for analyzing the inner structure of disordered systems, and frequently the application of this method is a unique way to obtain direct structural information on systems with random arrangement of density inhomogeneities in such large-scales. Currently, the SAS technique, with its well-developed experimental and theoretical procedures and wide range of studied objects, is a self-contained branch of

Source officielle

https://en.wikipedia.org/wiki/Small-angle_scattering

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La diffusion des rayons X aux petits angles (SAXS de l’anglais : Small Angle X-rays Scattering) est une technique expérimentale qui permet d’étudier les propriétés structurelles des matériaux à une éc

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Beam-based additive manufacturing (AM) typically involves high cooling rates in a range of 10(3)-10(4) K/s. Therefore, new techniques are required to understand the non-equilibrium evolution of materials at appropriate time scales. Most technical alloys have not been optimized for such rapid solidification, and microstructural, phase, and elemental solubility behavior can be very different. In this work, the combination of complementary in situ synchrotron micro-x-ray diffraction (microXRD) and small angle x-ray scattering (SAXS) studies with laser-based heating and rapid cooling is presented as an approach to study alloy behavior under processing conditions similar to AM techniques. In rapidly solidified Ti-48Al, the full solidification and phase transformation sequences are observed using microXRD with high temporal resolution. The high cooling rates are achieved by fast heat extraction. Further, the temperature- and cooling rate-dependent precipitation of sub-nanometer clusters in an Al-Cu-Mg alloy can be studied by SAXS. The sensitivity of SAXS on the length scales of the newly formed phases allows their size and fraction to be determined. These techniques are unique tools to help provide a deeper understanding of underlying alloy behavior and its influence on resulting microstructures and properties after AM. Their availability to materials scientists is crucial for both in-depth investigations of novel alloys and also future production of high-quality parts using AM.

Springer2016

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Early precipitation during cooling of an Al-Zn-Mg-Cu alloy revealed by in situ small angle X-ray scattering

Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven

Early subnanometre cluster formation during quenching of a high-strength AA7449 aluminium alloy was investigated using in situ small angle X-ray scattering. Fast quench cooling was obtained by using a laser-based heating system. The size and number density of homogeneous nucleated clusters were found to be strongly dependent on the cooling rate, while the volume fraction of cluster formation is independent of the cooling rate. Heterogeneous larger precipitation starts at higher temperatures in volume fractions that depend on the cooling rate. (C) 2014 AIP Publishing LLC.

American Institute of Physics2014

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Early cluster formation during rapid cooling of an Al-Cu-Mg alloy: In situ small-angle X-ray scattering

Jean-Marie Drezet, Patrick Schloth, Helena Van Swygenhoven

The formation of Cu-Mg clusters in an Al-Cu-Mg aluminum alloy is observed by small-angle X-ray scattering during cooling. Cooling rates are choosen to mimic the different conditions obtained at the surface and in the center of large forgings. Clusters of 0.45 nm start to form at 250 degrees C. Their volume fraction depends strongly on the cooling rate and the amount of excess vacancies. The difference in cluster kinetics explains the difference in rapid hardening across large forgings. (C) 2015 Acts Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Elsevier2015

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