Quantitative electron microscopy for microstructural characterisation

Development of materials for high-performance applications requires accurate and useful analysis tools. In parallel with advances in electron microscopy hardware, we require analysis approaches to better understand microstructural behaviour. Such improvements in characterisation capability permit informed alloy design. New approaches to the characterisation of metallic materials are presented, primarily using signals collected from electron microscopy experiments. Electron backscatter diffraction is regularly used to investigate crystallography in the scanning electron microscope, and combined with energy-dispersive X-ray spectroscopy to simultaneusly investigate chemistry. New algorithms and analysis pipelines are developed to permit accurate and routine microstructural evaluation, leveraging a variety of machine learning approaches. This thesis investigates the structure and behaviour of Co/Ni-base superalloys, derived from V208C. Use of the presently developed techniques permits informed development of a new generation of advanced gas turbine engine materials.Open Acces

Processing-Structure-Property Relationships in Ni-based Superalloy René 41

The cast and wrought Nickel based superalloy René 41 combines excellent strength, toughness, and corrosion properties. Its mechanical properties outperform all similar competitor aerospace alloys such as Waspaloy and Haynes 282. However, processing of René 41 remains challenging due to cracking and inhomogeneous grain size distributions, resulting in poor yield, limiting more wide-spread application. Therefore, despite having been developed in the 1950s, René 41 is not yet widely applied, and published research is limited. However, trends towards higher efficiency aircraft engines have now reignited interest in René 41 as a candidate material in next generation engines due to its excellent property profile. This necessitates new research to reduce the knowledge gaps in the processing-microstructure-property relationships of René 41. Correlative high-resolution microscopy is successfully applied to identify previously ambiguous secondary phases in René 41. This approach reveals complete space group, as well as high quality compositional information. These insights are applied to the development of an experimental precipitation study, and to update a current thermodynamic database for superalloys. The updated database has improved predictive quality regarding phase stability and composition of the grain boundary carbides M6C and M23C6. Applying these results to kinetic simulations also demonstrates higher predictive power. Such improved simulations are required to optimize the precipitation behaviour and predict material properties after processing. Comparison to literature data shows that the updated database yields improvements for other alloys besides René 41 as well, such as Haynes 282, Waspaloy and alloys in the Nimonic series. Further, dynamic restoration processes are studied based on laboratory scale hot-working experiments. Targeted design of the temperature profiles, allows the effect of nm scale γ’ precipitates on microstructural evolution to be isolated. Implementing the gained insights in simulations and phenomenological models advances the capabilities of modern software tools, providing better insights into microstructural processes. The results presented in this thesis will thus advance the understanding of the microstructural evolution in René 41 and the descriptive capabilities of modern thermodynamic simulation packages. This will facilitate higher yield in processing and enable future alloy design for next generation aerospace applications

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2021 (MC 2021) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2021"