Microstructure rearrangements in metals upon thermo mechanical processing followed by advanced in situ diffraction measurements

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Xiaojing Liu – PhD Candidate




In the early years of studying microstructure evolution, induced by thermo-mechanical processing, the most common approach was to measure quenched specimens after applying an appropriate temperature or mechanical load. Note that conventional post-processing characterization methods are sensitive to structural characteristics only in a thin near-surface layer and, generally, cannot be used to probe physical properties in the specimen’s bulk. Our research focuses on the application of advanced quantum beam techniques to in-situ studies of the heat- and pressure-assisted atomic and microstructure transformations in various metal alloys.

In-situ temperature-dependent neutron diffraction experiments were conducted to investigate the microstructural evolution of additively and conventionally manufactured CoCrFeNi high-entropy alloys, as-received and after grain refinement through high-pressure torsion conditions. Comparison between conventional and modified Williamson-Hall analysis revealed that the major contribution of micro-stress stems from a high dislocation density. Besides, the fully recrystallized nano-structured material shows the lowest dislocation density, which renders a recipe for stress release in additively manufactured materials.

In-situ temperature-dependent synchrotron diffraction experiments were performed on rolled sheet Mg alloys. The scattering-vector-time plots (QT plots) and azimuth-time plots (AT plots) have been collected in a wide temperature range. Dissolution of intermetallic phase Al12Mg17 was observed in AZ91.

Supervisors: Prof. Emil Zolotoyabko, Prof. Klaus Dieter-Liss