Project 8: Development of creep- and oxidation-resistant Cr-Mo-Si alloys

Doctoral researchers 

Dr.-Ing. Frauke Hinrichs (1st cohort)
M. Sc. Gabriely Falcão (2nd cohort) 
M. Sc. Sophie Hurst-Fraunhofer (3rd cohort)

 

Supervisors 

Prof. Martin Heilmaier,
Prof. Astrid Pundt

Project 

To improve the energy efficiency of turbine jet engines, a significant increase in operating temperatures is needed to replace the current state-of-the-art Ni-based superalloys (operated at around 1500 °C with the benefit of cooling). However, two major requirements, namely oxidation and creep resistance, are typically limited in all high-temperature alloy systems. 

During the two previous cohorts, a series of Cr-Mo-Si alloys has been investigated in order to determine a Cr/Mo ratio that can guarantee oxidation resistance in conjunction with adequate plasticity to perform at room and high temperatures. Among all tested alloys, the Cr-36-1Mo-3Si at.% has exhibited outstanding properties, including a high solidus temperature of around 1784 °C, extended plasticity even at room temperature, along with pesting and oxidation resistance up to 1100 °C. The addition of a new element to the reference alloy (Cr-36.1Mo-3Si at.%) has the potential to improve the creep performance by including a strengthening phase [1-4]. 

The third cohort of project 8 aims to answer the following questions: 

  1. Which element can promote the formation of a secondary strengthening phase without deteriorating the oxidation properties presented by the reference alloy?
  2. If a secondary phase is present, what is its morphology and spatial distribution within the microstructure? Is it located at grain boundaries, within grains, or at specific microstructural features? 
  3. What is the respective creep resistance and creep mechanism for the new alloy by comparing it to the reference alloy? 

 

Fig. 1: Data on the Cr-36.1Mo-3Si at.% alloy. (a) homogenized microstructure prior to testing. (b) SEM-EDS elemental maps and SEM-BSE micrographs of the oxide scales after 100 h of cyclic oxidation at 800 °C. (c) Samples after testing at 1, 10 and 100 h. (d) Compression test data at room temperature up to failure. (e) Twinning presence is indicated by the arrows. Figures taken from Ref. [1]. 

 

References 

[1]    F. Hinrichs et al., “A ductile chromium–molybdenum alloy resistant to high-temperature oxidation”, Nature 646 (2025), pp. 331-337, doi:10.1038/s41586-025-09516-8.
[2]    S. Obert, A. Kauffmann, and M. Heilmaier, “Characterisation of the oxidation and creep behaviour of novel Mo-Si-Ti alloys”, Acta Mater. 184 (2020), pp. 132-142, doi:10.1016/j.actamat.2019.11.045.
[3]    F. Hinrichs, “Gefüge und Oxidationsbeständigkeit einphasiger und mehrphasiger Cr-Mo-Si-Legierungen”, doctoral thesis, KIT (2024), doi:10.5445/IR/1000172819.  
[4]    F. Hinrichs et al., “A novel nitridation- and pesting-resistant Cr-Si-Mo alloy”, Corros. Sci. 207 (2022), 110566, doi:10.1016/j.corsci.2022.110566.