Accelerated Development of High-Performance Mo-Si-B-X Alloys via an Approach of Integrating Thermodynamic Modeling with Experimental Study

The proposed study aims at accelerated development of Mo-Si-B-X (X=Ti, Zr, Hf, Re, Mn) alloys with an optimized balance of properties, via an approach of integrating thermodynamic modeling with experimental study.   On the basis of the Mo-Si-B-X (X=Ti, Zr, Hf) database developed in Phase I, a thermodynamic database of the Mo-Si-B-O-X (X=Ti, Zr, Hf, Re, Mn) system will be developed using the Calphad approach. Critical experimental studies will be carried out to validate and optimize this database. A viscosity database for assessing the glass scale formation on the surface during oxidation will be developed in the same manner as the thermodynamic database development. Capabilities of the current software for multicomponent, multiphase equilibrium calculations will be extended to complex systems containing metal, oxide, liquid/glass, and gas phases. Functions for calculating the viscosities of the liquid/glass phase will be implemented. A range of alloy compositions with potentially improved overall performance will be identified with the aid of computational modeling and fabricated via powder metallurgy to obtain optimized microstructures. Their mechanical properties and oxidation resistance will be screened. Alloys with optimum properties will be selected for fabrication on a large scale, followed by full characterization of mechanical properties and oxidation resistance. BENEFIT: The proposed Phase II work will have broad impact on accelerated development of high-temperature, high-performance Mo-Si-B-X (X=Ti, Zr, Hf, Re, Mn) alloys. First, the thermodynamic database developed for the Mo-Si-B-O-X system is an important self-consistent knowledge bank. For example, it addresses the chemical driving forces for phase transformations and thermochemical stability of condensed metal and oxide phases. In combination with the Pandat software, this database can be used to calculate thermodynamic and phase equilibrium related properties of this system, such as phases formed, phase amounts, and phase compositions given alloy chemistry and temperature. Such information, critically needed for understanding the microstructure developed at different conditions, provides guidance in identifying Mo-Si-B-X alloys with potentially good oxidation resistance and mechanical properties. Second, the extended version of the Pandat software can be used to deal with complicated systems involving metals, oxides, liquid/glass, and gas phases. This will greatly enhance its current capability and broaden its applications in many other areas, such as metal-slag reaction in metallurgy, chemical vapor deposition (CVD), nitridation, and other metal-gas reactions. Third, and most importantly, the optimized Mo-Si-B-X alloys identified in this study will make a great impact for applications at higher temperatures where current Ni-based superalloys are not suitable.