Project

Discipline

Lead
Lay summary
At the frontier of research in novel engineering materials is the understanding of the relationship between microstructure and materials properties. It is well known that the dynamics of dislocation and other defect structures play an important role in the mechanism of metals plasticity and failure under stress. Diffraction is very sensitive to the strain fields related to the defect structures and is therefore the method of choice to study the evolution of dislocation densities. Experimental methods based on x-ray and neutron diffraction at synchrotron and neutron sources have made giant steps forward in terms of instrumentation and available intensities. It is now possible to acquire high quality data sets in situ at or below the millisecond scale. On the other hand, for interpreting this wealth of data, theoretical methods have not been significantly advanced since the ‘70s - with the outstanding (but nowadays too limited) works of Krivoglaz and Wilkens. The aim of this project is to break new ground in the interpretation of diffraction data (both powder diffraction and polychromatic Laue diffraction) by improving the understanding of the link between the parameterization of the diffraction profile and the underlying microstructure. Bottom-up approaches are aimed for in which a set of advanced tools for fast calculation of diffraction profiles will be developed.

Direct link to Lay Summary

Last update: 21.02.2013

Number	Title	Start	Funding scheme

At the frontier of research in novel engineering materials is the understanding of the relationship between microstructure and materials properties. In order to design improved structural materials we need to understand what happens on the atomic scale when the material is pushed into extreme conditions (temperature, stress, pressure, corrosion). It is well known that the dynamics of dislocation and other defect structures play an important role in the mechanism of metals plasticity and failure under stress. Diffraction (x-ray, neutron) is very sensitive to the strain fields related to the defect structures and is therefore the method of choice to study the evolution of dislocation densities. Experimental methods based on x-ray diffraction at synchrotron sources have made giant steps, so that it is currently possible to acquire excellent data sets in situ at or below the millisecond scale. On the opposite, for interpreting this wealth of data, theoretical methods have not been significantly advanced since the ‘70s - with the outstanding (but nowadays too limited) works of Krivoglaz and Wilkens. The aim of this project is to break new ground in the interpretation of diffraction data (either powder diffraction or polychromatic Laue diffraction). Firstly, we shall hone and develop a set of advanced tools (Debye function methods, finite elements decomposition) for fast calculation of diffraction. These will enable us to evaluate diffraction patterns of specimens under complex strain fields with much faster computation times than currently possible. Thereby we aim to provide a link between theoretical calculations and diffraction experiments. A second, more ambitious and extensive aim is to use atomic scale computational results in order to extend and refine current macroscopic theories of Krivoglaz and Wilkens, now quite limited, to include more complex and realistic cases. Finally, as a far-field target, we aim to improve the understanding of the link between macroscopic parameterization and the atomic scale. The new methods developed will be validated by suitable, dedicated test experiments performed at the Swiss Light Source synchrotron and elsewhere, exploiting also planned collaborations. The current proposal requests the financial support during 2 years of a post-doc position to develop new theoretical/computational tools that can then be used for the interpretation of experiments performed at 3 beamlines that are frequently used to explore dislocation densities/distributions in metallic materials and this often by performing in-situ testing.