"Application of X-ray imaging to the study of metal alloy solidification: how in situ visualization changed our way of looking at microstructure formation"
Structural material properties are directly related to their solidification microstructure, so that a precise control of the growth process is crucial in engineering. The most common microstructure is the dendrite (as with snowflakes), which can be either columnar or equiaxed. The dendritic grain structure is called columnar if the growth is preferentially oriented in a direction close to the heat flux, whereas equiaxed grains are growing in all space directions, leading to a material with more isotropic macroscopic mechanical properties and a more homogeneous composition field than with columnar microstructures. Depending on the application, one type of grain structure is usually preferred, e.g. equiaxed grains in car engines and columnar grains in turbine blades. In addition to its industrial relevance, the development of the complex dendritic morphology is a typical example of out-of-equilibrium pattern formation, so that the prediction and control of solidification microstructures in alloys actively stimulates abundant laboratory research, linking fundamental and applied sciences.
The advancement of in situ experimental methods for real-time observation of the propagating solid-liquid interface during solidification is essential to improve the understanding of this process and to test analytical models and numerical simulations. Major theoretical breakthroughs have been achieved by studying organic materials that solidifies like metals and are transparent to visible light. During the last decade, in situ and real-time visualization by using X-ray imaging has become a method of choice for unveiling the dynamical formation of the solidification microstructures and grain structure directly in metal alloys. This lecture will show how X-ray imaging techniques (radiography, topography also called diffraction imaging, tomography) can be applied to the study of microstructure formation in metal alloys, and the complementary information they can provide for comparison with models. Particular emphasis will be placed on the progress obtained at synchrotron sources as well as on recently developed laboratory devices.
Faculty Host: Dr. Hani Henein
After a PhD in materials science (2006) at Aix-Marseille University and a post-doc at both ESRF (European Synchrotron Radiation Facility) and ILL (Institut Laue-Langevin neutron source) as an ESA (European Space Agency) fellowship, Guillaume Reinhart was nominated assistant professor in 2009 at Aix-Marseille University and joined the IM2NP (Institut Matériaux Microélectronique Nanoscience de Provence) laboratory.
The main axis of his research is the investigation of microstructure formation in metal alloys by using in situ observation techniques. He actively participated in the application of X-ray imaging techniques to the study of the solidification of Aluminum-based alloys and received the C.H. Mathewson award of TMS in 2010 for the experimental results obtained by combining the synchrotron radiography and topography observation techniques.