Thermodynamic modeling

The selection of high temperature materials for applications in corrosive environments requires careful consideration of various factors, with an emphasis on balancing mechanical performance and oxidation/corrosion resistance. This research topic focuses on the application of thermodynamic modeling techniques to the development of high temperature alloys by predicting phase formation, phase transition and microstructural evolution over different compositions and temperature ranges. This predictive capability enables the development of novel alloy compositions with improved mechanical properties and higher resistance to gas corrosion for high temperature applications.

Corrosion mechanisms and kinetics in various gases

This research topic aims to elucidate the corrosion mechanisms and kinetics of materials exposed to various gases such as air, oxygen, steam, and hydrogen-containing gases at high temperatures.

Thermogravimetric analyses (TGA) are performed to determine the mass changes of the samples during oxidation, providing valuable insights into the corrosion behavior and kinetics of the materials under specific environmental conditions. Isothermal and cyclic oxidation tests are conducted to obtain important parameters for evaluating the long-term durability and reliability of materials in practical applications. In addition, the morphology and microstructure of corroded materials are characterized using advanced spectroscopy and microscopy techniques (XRD, SEM, TEM, etc.). These analyses help to identify corrosion products and mechanisms and contribute to a comprehensive understanding of material degradation under high-temperature conditions.

Recent alloy developments show that the growth of a protective and compact complex CrTaO₄ oxide layer on some refractory CCAs such as TaMoCrTiAl enables excellent oxidation resistance, with oxidation kinetics at high temperatures lower than those of a Cr₂O₃ layer.

Strategies for increasing corrosion resistance

This research topic focuses on analyzing corrosion-related material degradation and developing effective strategies to extend the service life of components and structures at high temperatures. By integrating findings from studies on corrosion mechanisms and kinetics, we aim to identify the most important corrosion-related failure modes and proactive protection approaches in order to further improve the corrosion resistance of newly developed alloys.

Examples of corrosion protection strategies for TaMoCrTiAl-CCAs include doping with silicon or high-valent elements such as tungsten (W) and rhenium (Re) to reduce the oxygen vacancy density in the CrTaO₄ layer, which not only reduces the growth rate of the oxide layer but also the extent of internal oxidation. In addition, physical vapor deposition (PVD) has been used to apply more corrosion-resistant coatings to various alloy systems.

Equipment

In cooperation projects funded by the DFG, HGF, BMWK and others, we are working on the development of novel high-temperature alloys and research into their degradation mechanisms under extreme operating conditions:

•     Development of novel Ti-based alloys with improved thermal-mechanical properties
•     Formation and growth mechanisms of CrTaO4 layers and improvement of their properties on relevant high-temperature materials
•     Refractory metal-based alloys with integrated coatings for aerospace applications
•     Materials Compounds from Composite Materials for Applications in Extreme Conditions (MatCom-ComMat)