Fundamental characterization of novel Mo-Si-B-Ti-alloys at ultra-high temperatures

• Applicants: Professor Dr.-Ing. Hans Jürgen Christ; Professor Dr.-Ing. Martin Heilmaier
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Synthesis and Properties of Functional Materials ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 236295902

The aim of the intended research project is the development of new, structural Mo-Si-B-based alloys with improved properties for application temperatures up to 1300°C. In the course of the first funding period we succeeded in the alloy development to broaden significantly the ternary Moss-T1-T2 phase field in the Mo-Si-B-Ti system with small amounts of Fe. We produced for the first time ternary alloys containing the (Mo,Ti)5Si3 phase with excellent oxidation resistance at 750-1300°C. The catastrophically oxidizing (Mo,Ti)3Si phase could be avoided utilizing the arc-metallurgical processing route. It was found that Mo-Si-B-Ti-alloys outplay both the Mo-Si-B alloys and the Ni-based singly crystal alloys with respect to mechanical, i.e. creep, properties. Regarding the high temperature oxidation behaviour fundamental knowledge for the specific adjustment of a protective SiO2-TiO2-duplex layer has been gained due to the fruitful cooperation of the both institutions KIT and USiegen. In addition, sufficient experimental data have been collected for a sound, realistic simulation of inner and outer oxidation processes which will serve as an important tool for the exploitation of the existing potential of Mo-Si-B-Ti-Fe alloys. Greatest endeavor of the present proposal will be the determination of the chemical composition of technically applicable Mo-Si-B-Ti-Fe alloys. Main emphasis will be placed on the impact of the observed Ti-silicides on the already excellent mechanical properties and the intrinsic oxidation resistance. This implies the extensive characterization of the microstructure, the nature/effect of the Ti-silicide precipitates on the deformation behaviour of the solid solution phase and the isothermal/cyclic oxidation resistance of Mo-Si-B-Ti-Fe alloys. To enable an efficient development cycle, the evaluation of the alloy compositions with an improved balance of mechanical and oxidative properties should occur by the interplay between mechanism-based simulation and experimental results. The assessment of the oxidation process of different Mo-Si-B-Ti-Fe alloys has to be performed dependent on the temperature, the microstructure and the chemical composition using a FEM model considering the real microstructure by embedding spatially- and time-resolved kinetic calculations as well as local thermodynamic equilibrium calculations. Selected compositions with simulation based predicted property improvement shall be produced and investigated to verify the simulation model.

• DFG Programme: Research Grants