Project 14: Analysis of structure-property relationships in molybdenum-based high-temperature alloys by advanced electron microscopy
Doctoral researchers
Dr. Hemanth Thota (1st cohort)
M. Sc. Mareike Dortmund (2nd cohort)
Supervisors
TT-Prof. Yolita Eggeler,
Prof. Astrid Pundt
Project
Modern high temperature structural components demand a fundamental understanding how atomic and microstructural features influence macroscopic material properties. Defects, phase boundaries and chemical heterogeneities play a key role in determining mechanical and functional behaviour. [1]
Electron microscopy provides powerful tools to study these relationships across multiple length scales. Techniques such as high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) enable detailed characterisation of structure, composition and functionality.
Molybdenum based silicide alloys (e.g. MoSiTi and MoCrSi) are promising high temperature material, due to their high melting point, oxidation resistance and strength. However, their performance is strongly affected by microstructural evolution, including twinning, precipitation and segregation. [2,3]
Previous studies have revealed unexpected twin formation in MoCrSi alloys at elevated temperatures, challenging established assumptions regarding deformation and defect mechanisms, indicating previously unexplored mechanisms of microstructural evolution. [4] The analysis of this twin formation is a central aspect of this project. It offers the opportunity to critically question and further develop existing models of high temperature deformation. The project addresses how micro- and nanoscale structures and local chemical variations control the properties of Mo-based alloys. It focusses on (i) the conditions triggering twinning in MoCrSi at high temperatures, (ii) the role of chemical segregation and phase boundaries stabilising twins and (iii) the impact of twinned microstructures on mechanical properties.
References
[1] Reed, R.C., Tao, T., Warnken, N., Alloys-By-Design: Application to nickel-based single crystal superalloys, Acta Mater. 57, 5898-5913 (2009), DOI: 10.1016/j.actamat.2009.08.018.
[2] Hinrichs, F., Kauffmann, A. et al., A novel nitridation- and pesting-resistant Cr-Si-Mo alloy, Corrosion Science 207, (2022). DOI: 10.1016/j.corsci.2022.110566.
[3] Schliephake, D., Kauffmann, A., et al., Constitution, oxidation and creep of eutectic and eutectoid Mo-Si-Ti alloys, Intermetallics 104, 133-142 (2019), DOI: 10.1016/j.intermet.2018.10.028.
[4] Hinrichs, F., Winkens, G., Kramer, L.K., et al., A ductile chromium–molybdenum alloy resistant to high-temperature oxidation. Nature 646, 331-337 (2025). DOI: 10.1038/s41586-025-09516-8.
During its 1st doctoral cohort, the project was named "Elementary nanoscale mechanisms which govern nucleation, growth, oxidation and deformation processes in the high temperature Mo-Si-Ti system: Advanced in situ and ex situ TEM analysis" and focused on the identification of elementary deformation processes on the nano scale, which govern creep of Mo-Si-Ti alloys. Creep/oxidation interaction phenomena received special attention. Interrupted creep experiments were analyzed in terms of deformation structures and regarding oxidation products. An effort was made to single out the dominant deformation mechanism. Investigations were performed on series of interrupted specimens which were creep exposed at different temperatures. Changes in local alloy chemistry during high temperature exposure were analyzed and efforts made to quantify atomic fluxes associated with microstructural evolution and high temperature oxidation.
Publications
[5] Thota, H., Schliephake, D., Kauffmann, A., Wu, H., Pundt, A., Heilmaier, M. and Eggeler, Y. M. (2024), The Creep-Induced Micro- and Nanostructural Evolution of a Eutectic Mo–Si–Ti Alloy at 1200 °C. Adv. Eng. Mater. 26, 2301909. DOI: 10.1002/adem.202301909.
[6] Schliephake, D., Ramdoss, S. R., Vikram, R. J. et al., Microstructure and mechanical properties of a laser-based directed energy deposited Mo-Si-Ti alloy. J. Mater. Sci. 60, 18246-18260 (2025). DOI: 10.1007/s10853-025-11158-0.
[7] Thota, H., Schliephake, D., Kauffmann, A., Wu, H., Pundt, A., Heilmaier, M., Eggeler, Y. M., Creep-induced microstructural evolution of the eutectic Mo-Si-Ti alloy by correlative electron microscopy, BIO Web Conf. 129, 23022 (2024), DOI: 10.1051/bioconf/202412923022.