Stored energy in plastically deformed metals

Physical properties of metals and alloys are influenced by lattice defects present in the crystal, which generally are surrounded by an elastic strain field. Accurate determination of the corresponding strain energy is extremely important in practice since it serves as reference for checking the existing theories linking the microstructure to macroscopic physical properties. For example the stored energy is considered as the driving force for recrystallization, a very old, but still unsolved problem in materials science. The reason is the lack of a general theory/model that captures the complex microscopic processes acting during metal forming and heat treatment. For single-phase materials, the main mechanisms are plastic deformation, recovery, and finally the germination and growth of new grains. Many studies show that several factors contribute, to varying degrees, to recrystallization but, without exception, all emphasize the importance of the plasticity induced stored energy.

During this thesis we will study the recrystallization of a model Fe-3%Si alloy. The alloy will be first cold-rolled and then the deformed state characterized by electron microscopy (EBSD) and X-ray diffraction. The dislocation density and the stored energy will be determined from the data obtained with two methods. Finally, the comparison of the results obtained with the two techniques will be performed and the description of the heterogeneity of the plastic deformation will be obtained. The latter expresses the variation of the dislocation density as a function of grain crystallographic orientation. In the second part of the PhD in situ experiments will be performed at ESRF using the scanning 3DXRD method. This will allow determining the strain at the intragranular level.

Data evaluation will be performed with already existing scientific software, but basic knowledge of Python is necessary.

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The candidate should have a good background in materials science or physics

The knowledge of Python programming language is necessary