Synchrotron High-Energy X-ray & Neutron Diffraction, and Laser-Scanning Confocal Microscopy: <i>In-Situ</i> Characterization Techniques for Bulk Nanocrystalline Metals

Abstract

This report is aimed at giving an overview of the significance of the novel and innovative microstructural and microscopic characterization techniques for bulk nanostructured metals processed by severe plastic deformation, specifically high-pressure torsion (HPT). In practice, the microstructural relaxation behavior upon heating of nanostructured 316L stainless steel and CoCrFeNi high-entropy alloy was characterized by in-situ heating neutron diffraction measurements; the heterogeneous phase distribution of an HPT-bonded hetero-nanostructured AlMg alloy was examined using synchrotron high-energy X-ray diffraction; and the microstructural evolution upon heating of a nanostructured CoCrFeNiMn high-entropy alloy was examined by laser-scanning confocal microscopy. These novel techniques are complementary to each other and any other in-or ex-situ testing methods, especially when nanocrystalline metals are transforming microstructurally and compositionally with temperature and time in a hierarchical manner. The outcomes of the studies emphasize the importance of the methodologies and the development of characterization techniques for further in-depth exploration in the research field of severe plastic deformation.

The Cold Angular Rolling Process of Copper Sheets: Unraveling Plastic Deformation Behavior and Unveiling Microstructural Transformations

“…A recent report provides an overview of synchrotron X-ray and neutron diffraction techniques applied to HPT-processed nanocrystalline materials to characterize their microstructural heterogeneity and in situ heating relaxation behavior. [128] A preliminary result shows the regional and hierarchical phase transformation upon heating over a wide sample surface of the HPT-processed alloy using high-temperature laser-scanning confocal microscopy. Regarding bulk mechanical properties, micro-and nanoscale indentation methods have been used to characterize samples with small volumes, [15,129] and hardness mapping as Figure 3b reveals the inhomogeneity of hardness distributions over the large areas.…”

In-situ neutron and synchrotron methods for the investigation of plastic deformation and annealing in metals

“…A comprehensive table has been published by Kawasaki et alii, listing both neutron and synchrotron studies on specimens after severe plastic deformation and their conditions of investigation [24]. An early study combining both synchrotron and neutron diffraction on highpressure torsion processed material has been undertaken on a twinning-induced-plasticity steel, revealing the local and global stress induced martensitic transformation from α-Fe to ε-Fe phase, retained in the ultrafine-grained microstructure, alongside a texture analysis [25].…”

“…Altogether, this Xray and neutron combined study distinguishes local and global structural evolution, revealing that there exist higher plastically strained zones in the surface-near region of a high-pressure torsion specimen than in the bulk. Further inhomogeneities and their thermal evolution have been imaged by laser scanning confocal microscopy by Kawasaki et alii on high-entropy alloy specimens [24]. Reproduced from [28].…”

In-situ heating observations on microstructure relaxation of ultrafine-grained high-entropy alloys using neutron diffraction and laser-scanning confocal microscopy

“…The in-situ neutron diffraction experiments provide a knowledge base to minutely design crystalline microstructures and improve the desired properties of a UFG material by an accurate post-processing heating treatment. A recent report summarized currently available examples of SPD-processed nanostructured materials which are characterized by synchrotron X-ray and neutron diffraction techniques [17].…”