CCS and Power Systems

Crosscutting Research - University Training and Research

Computational Studies of Physical Properties of Nb-Si Alloy

Project No: FE0003798

Project Description

Niobium-silicon based alloys are highly promising materials for use in next generation turbines operating at the elevated temperatures required for advanced power generation systems. Niobium has an array of attractive properties for high-temperature applications, but it suffers from low oxidation resistance and modest high-temperature mechanical properties. Alloying Nb with Si introduces intermetallic phases that significantly improve its high-temperature mechanical properties. The intermetallic phases have a high melting point, but are brittle at room temperature. However, by incorporating a ductile Nb solid solution phase, the resulting composite can be strengthened. Some roadblocks to their eventual industry acceptance remain. Alloying with a third element has been shown to improve oxidation resistance. The evolution of Nb-Si alloy development is very complex with the alloy often being composed of more than seven elements.

In an effort to manage this complexity and further the development of a suitable Nb-Si based alloy, the project team will provide physical properties data supplementing experiments for thermodynamic modeling, phase field simulation for microstructure, and continuum simulations for mechanical properties of these alloys. The project team will further develop their Gibbs free energy package to support free energy calculations of structure types. The project team will then develop an interface between the Gibbs free energy package G(P,T) and the popular Calculation of Phases Diagram (CALPHAD) software Thermo-Calc®. The integrated tool will be utilized to study thermodynamic properties of various phases found in Nb-Si-based alloy with a focus on the quaternary system Nb-Si-chromium (Cr)-X—where X is some other metal, such as titanium (Ti), aluminum (Al), hafnium (Hf), or molybdenum (Mo).

The project will also study interfaces found in the Nb-Si based alloys. Structural models for the interfaces among the main bulk phases, the Nb solid solution, and Nb silicides will be developed. Formation energies of the undoped and doped Nb-Si-Cr will be calculated and compared. Interfacial mechanical properties will be evaluated using similar approaches developed for ceramic interfaces.

Project Details