Oxidation-resistant Mo-base alloys by application of oxidation protection coatings of ternary Zn-Mo oxides

• Applicants: Dr. Ulf Betke; Professorin Dr.-Ing. Manja Krüger
• Subject Area: Coating and Surface Technology ; Solid State and Surface Chemistry, Material Synthesis ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 579835459

Mo-base alloys show promising mechanical properties and high-temperature stability. However, they are prone to catastrophic oxidation in oxidizing atmosphere at temperatures above 250 °C due to evaporation of MoO3. These oxidation reactions can be hindered by ü protective coatings in order to stabilize the material in oxidizing environment at elevated temperature. The project aims on an unprecedented approach of applying a zinc oxide based oxidation protection coating onto Mo-base alloys. TZM (Mo with < 1 % Ti/Zr) will be used as a model system as it has superior (thermo)mechanics properties compared to pure Mo, but the same oxidation problem. Zinc oxide, ZnO is capable of reacting with Mo oxides into stable ternary compounds like ZnMoO4 or Zn2Mo3O8. The proposal is based on the hypothesis, that these ternary Zn-Mo oxides form a stable and oxygen-impermeable coating on the TZM substrate and protect the material against oxidation. Preliminary studies on ZnO-Mo pellets suggested validity of this hypothesis and identified the compound Zn2Mo3O8 as phase with the highest potential for oxidation protection. The project is structured into several sub-tasks: At first, the solid-state reactions and process parameters for synthesis of the phase Zn2Mo3O8 from ZnO, Mo and MoO2 will be investigated. Based on this, a suitable procedure for coating TZM with Zn2Mo3O8 is developed and applied. Here, a reactive coating process using a ZnO powder bed - similar to pack cementation - is intended. The applied coatings are to be investigated with respect to their microstructure and interface to the substrate. Based on this, a suitable set of process parameters for Zn2Mo3O8 coating of TZM is derived. The obtained TZM substrates with Zn2Mo3O8 coating are then subjected to isothermal and cyclic oxidation tests at temperatures up to 1000 °C and 500 hours. Based on these experiments, the oxidation protection potential of the coatings and the oxidation kinetics will be derived. All obtained results will be summarized in an empirical model, which allows a qualitative evaluation of the oxidation resistance of TZM with Zn2Mo3O8 coating.

• DFG Programme: Research Grants