Ab-initio calculation and thermodynamic modeling of Mo-Si-B ternary system

• Grant number: 21/06318-9
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): August 01, 2021
• Effective date (End): July 31, 2022
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Luiz Tadeu Fernandes Eleno
• Grantee: Pedro Luís Rodrigues de Almeida
• Host Institution: Escola de Engenharia de Lorena (EEL). Universidade de São Paulo (USP). Lorena , SP, Brazil

Abstract

Alloys for high-temperature applications are generally based on binary or ternary systems containing refractory metals, such as Nb or Mo, often modified by Si or B. Such multiphase, multicomponent materials show a good resistance to corrosion, but, to ensure structural stability at high temperatures during the long life cycle, one or more protective layers are required. Usually a bonding layer (Fe, Cr, Al, Ru) is applied between the substrate (Nb- or Mo-based alloys) and anti-oxidation coatings (Fe, Cr, Si, B). The knowledge of the existing phases and thermodynamic equilibria among them are of the utmost importance, as the reactivity between the layers is very sensitive to temperature. Among the most promising systems are the Mo-Si-B ternary alloys. In particular, the T2 phase, of composition Mo5SiB2, has an excellent balance between resistance to oxidation and mechanical properties at high temperatures. Despite the extensive literature available on Mo-Si-B properties, the existing thermodynamic descriptions are all based only on experimental data from the binary and ternary systems. The present undergraduate project aims, therefore, to update the thermodynamic description of the Mo-Si-B ternary system using experimental and ab-initio data, following the Compound Energy Formalism (CEF) models within the scope of the CALPHAD for the phase diagram calculation, and the Density Functional Theory (DFT) for the estimation of formation energies that can be used directly in the thermodynamic description. (AU)