Joint ESRF-ILL colloquia
Monday, 4 July 2022, at 2:00 p.m
Neutron and High Energy X-ray (> 30 keV) diffraction provide the opportunity to quantitatively probe the microstructure of materials at bulk depths under extreme environments. Recent interest in advanced manufacturing techniques have driven coupled experimental/theoretical studies focused on accelerated science-based qualification of materials under manufacturing conditions. Diffraction experiments can be imagined under many different manufacturing conditions, but as metal Additive Manufacture (AM) has garnered so much interest lately, our work and this talk will focus on conditions relevant to AM. In particular, we will focus on designing scattering experiments to extract quantitative microstructural information, e.g., phase fraction, texture, internal stress, solute chemistry and dislocation density during manufacturing processes. The desire for microstructural information, that is phase fraction rather than peak intensity for example, often forces sacrifices either in the fidelity of the experimental environment to the actual process, or in the maximum rate of data collection. Thus, it is necessary to carefully select the probe, X-rays or Neutrons, to match the data rate to the kinetics of the specific process of interest. In this work, we have collected diffraction data during in-situ AM and during post-build processing of several relevant metal alloys to monitor the microstructural evolution of the material, expressly for the purpose of developing and validating microstructure-aware process models. The observed microstructure evolution for each case will be presented, and the necessary assumptions made in extracting the microstructural information from diffraction data will be critically examined.
1Brown, D.W., 1Carpenter, J. S, 1Clausen, B., 2Strantza, M.
2Los Alamos National Laboratory, Los Alamos, NM 87544
3Lawrence Livermore National Laboratory, Livermore, Ca
Monday, 7 March 2022
At DLR research in the field of materials physics under microgravity conditions is devoted to exploration of the fundamental mechanisms that underlie properties of, and solidification processes in metallic liquids in particular, and disordered media in general. Experiments on these systems are often hampered by gravitationally driven phenomena like convection or sedimentation. The challenge is, therefore, to provide experimental techniques under well-defined conditions where accurate and precise measurements of physical quantities become possible. In recent years the measurement of self- and interdiffusion coefficients in liquid metals and alloys has evolved tremendously through the development of new experimental techniques that observe diffusion processes in-situ on ground and under microgravity conditions with X-ray radiography.
This research is complemented with X-ray and neutron diffraction, and quasielastic neutron scattering. The combination with electrostatic levitation of the liquid sample droplets gives access to the measurement of partial structure factors, structural relaxation and atomic diffusion with unequalled accuracy so far. Results are discussed in the context of the relation of self- and interdiffusion (Darken’s equation), of the relation of self-diffusion and viscosity (Stokes-Einstein relation), structure-property relations (Mode-Coupling-Theory), modelling of dendritic growth, and liquid-liquid transitions.
In this presentation the interplay between scientific findings, the development of measurement techniques, and the realization of flight hardware is illustrated with selected flight experiments during parabolic flight, on sounding rockets, and aboard the International Space Station.
Friday, September 24th, 2.00.PM CET
Understanding how and when molecular solid hydrogen may transform into a metal has stimulated many theoretical works since the 30’s.
It is still an opened theoretical question and an experimental challenge. The quest for metal hydrogen has pushed major developments of modern experimental high pressure physics and still various claims of its observation have remained unconfirmed. In 2020, we observed and characterized the transition to metal hydrogen near 425 GPa at 80 K . Very recently, the transition to metal deuterium has also been observed, showing a significant isotopic shift in pressure. In this talk, our experimental strategy will be presented as following three steps namely:
1) Demonstrate the possibility to generate pressures well over 400 GPa ( that is the limit of the conventional Diamond Anvil Cell (DAC)) by loading hydrogen in the recently developed Toroidal-DAC;
2) Exhibit a reliable non-intrusive signature of the insulator-metal phase transition, i.e. total IR absorption by using the IR synchrotron radiation at SOLEIL;
3) Record combined infrared, Raman and visible observation measurements to disclose the physics at stake at the insulator-metal transition.
On-going experimental developments to further characterize the intriguing properties of metal hydrogen will be discussed.
 Synchrotron infra-red spectroscopic evidence of the probable transition to metal hydrogen. P. Loubeyre, F. Occelli and P. Dumas. Nature 577, 631 (2020).
 Toroidal diamond anvil cell for fine measurements under extreme static pressures: data on Al, Ar and Au up to 603 GPa. A. Dewaele, P. Loubeyre, F. Occelli, O. Marie and M. Mezouar. Nature Com. 9, 2913 (2018).