Colloquia Series on Sustainable Metallurgy

Challenges and Perspectives for the Development of
High Temperature Materials

Speaker: Prof. Alexander Kauffmann, Materials Science
and Engineering, Ruhr University Bochum

Host: on invitation of Prof. Erik Bitzek

Abstract

Kauffmann, A.; Obert, S.; Schliephake, D.; Hinrichs, F.; Winkens, G.; Falcão, G.; Eusterholz, M.; Tirunilai, A. S.; Gombola, C.; Thota, H.; Cong, X.; Beichert, B.; Kramer, L. K.; Gorr, B.; Christ, H.-J.; Eggeler, Y.; Galetz, M. C.; Inui, H.; Heilmaier, M.

Despite the rapid advancement of renewable energy sources, enhancing the efficiency of energy conversion from fossil or synthetic fuels remains crucial for achieving climate goals, as some technologies—such as aircraft propulsion—may not transition to full electric power within the next few decades. Consequently, further efficiency improvements are necessary, for instance, through enhanced high-temperature capabilities. Although refractory element-based alloys have long been considered promising candidates to overcome the limitations of Ni-based superalloys, fundamental barriers to their application have often not been addressed in materials development.

This presentation will discuss recent advancements in addressing the most challenging barriers to the application of refractory metals and alloys: catastrophic oxidation and limited ductility. As these aspects are related to fundamental mechanisms operating at different length scales, their prediction through simulations remains elusive. Therefore, materials development relies on metallurgical design strategies and experiments. Over the past decade, phase and microstructure design have enabled the suppression of critical volatile or voluminous oxide formation by strategically selecting and distributing passivating elements to protect the alloys effectively. While these materials exhibit in some cases impressive oxidation resistance, they often lack sufficient ductility. Recently, this challenge has been addressed through the successful synthesis of ternary Cr-Mo-Si solid solutions that combine high strength, decent oxidation/nitridation resistance, and compression ductility. This achievement is attributed to the unexpected activation of deformation twinning alongside dislocation-mediated plasticity over a broad temperature range.

The presentation will introduce relevant strategies to protect refractory element-based alloys from catastrophic and high-temperature oxidation, culminating in the recent observation of oxidation-resistant solid solutions that exhibit unusual deformation mechanisms. The sustainability of these novel alloys will briefly be assessed.

 After working at the Leibniz Institute for
 Solid State and Materials Research
 Dresden and the Karlsruhe Institute of
 Technology (KIT), Professor Kaufmann
 received an assignment at the Ruhr
 University this year. In 2024, the German
 Materials Research Society awarded him
 the Masing Memorial Prize.