In situ mapping of chemical segregation using synchrotron x-ray imaging

Abstract

Synchrotron x-rays are a powerful tool to probe real-time changes in the microstructure of materials as they respond to an external stimulus, such as phase transformations that take place in response to a change in temperature. X-ray imaging techniques include radiography and tomography, and have been steadily improved over the last decades so that they can now resolve micrometer-scale or even finer structural changes in bulk specimens over time scales of a second or less. Under certain conditions, these imaging approaches can also give spatially resolved chemical information. In this article, we focus on the liquid to solid transformation of metallic alloys and the temporal and spatial resolution of the accompanying segregation of alloying elements. The solidification of alloys provides an excellent case study for x-ray imaging because it is usually accompanied by the progressive, preferential segregation of one or more of the alloying elements to either the solid or the liquid, and gives rise to surprisingly complex chemical segregation patterns. We describe chemical mapping investigations of binary and quasi-binary alloys using radiography and tomography, and recent developments in x-ray fluorescence imaging that offer the prospect of a more general, multielement mapping technique. Future developments for synchrotron-based chemical mapping are also considered.

Acknowledgments

Shikang Feng is a postdoctoral research assistant in the Department of Materials at the University of Oxford, UK. He obtained his BSc degree in materials science and engineering from The University of Manchester, UK, and his doctorate in materials from the University of Oxford in 2020. His research focuses on using x-ray imaging to understand fundamental dynamics and kinetics involved in metal solidification processes, with a particular interest in second-phase intermetallic compounds. Feng can be reached by email at shikang.feng@materials.ox.ac.uk.

Enzo Liotti is a departmental lecturer in the Department of Materials at the University of Oxford, UK. He obtained his BSc and MSc degrees in materials engineering from the Politecnico di Milano, Italy, and his PhD degree in materials science in 2011 from the Loughborough University, UK. His research includes using and developing x-ray synchrotron techniques for the investigation of fundamental dynamic phenomena in metal processing and materials science, with a focus on the solidification of metal alloys and elemental segregation. Liotti can be reached by email at enzo.liotti@materials.ox.ac.uk.

Matt Wilson is the head of the Detector Development Group in the Technology Department at the Rutherford Appleton Laboratory, UK. He has 14 years of experience and more than 50 publications in detector technology. He has delivered scintillator and solid-state x-ray detector systems for a range of scientific applications from astrophysics to synchrotron science. He developed the HEXITEC detector systems, and led the academic and commercial uptake of the technology. Wilson can be reached by email at matt.wilson@stfc.ac.uk.

Lydia Jowitt is a graduate detector scientist in the Detector Development Group at the Science and Technology Facilities Council at Rutherford Appleton Laboratory, UK. She received her MPhys degree from the University of Oxford, UK, in 2019. Her research focuses on developing a lens-coupled scintillator detector system, characterizing HEXITEC detectors, and analyzing data from synchrotron experiments. Jowitt can be reached by email at lydia.jowitt@stfc.ac.uk.

Patrick Grant is a Vesuvius Chair of Materials and Pro-Vice-Chancellor for Research at Oxford University, UK. His research includes developing and understanding novel methods of materials manufacture, especially the evolution of material microstructures across a range of length scales. His current research focuses on the manufacture of supercapacitors and batteries, three-dimensional printing, and new alloys and processes for more tolerant materials recirculation. Grant can be reached by email at patrick.grant@materials.ox.ac.uk.