Entwicklung und Erweiterung der thermodynamischen Datenbanken für die Systeme V-Si-B und V-Ti-B

Refractory metals are increasingly becoming the focus of scientific research and development. They present a highly attractive alternative to the current state-of-the-art nickel-based superalloys. Their high melting temperatures and good formability at elevated temperatures align with the required properties for high-temperature applications. Despite their exceptional characteristics, refractory metal-based systems are inadequately explored, particularly regarding their chemical properties, such as corrosion resistance, the formation and composition of oxide layers, thermochemical stability, and similar aspects.
The objective of this study is the development and expansion of a thermodynamic database, intended as a supportive tool for the research of new vanadium-based alloys. Using the FactSage™ software, literature-published datasets for the binary and ternary systems of the elements V, Si, B, Ti, and Cr were consolidated into a unified database. The dataset for the ternary system V-Ti-B was fundamentally newly generated. Microstructural analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), were conducted on eight V-Ti-B alloys to experimentally determine the phase compositions and fractions. The validation of the generated dataset was carried out by comparing the experimentally determined results with those calculated by the software.
The prediction accuracy of the dataset exhibited a deviation range of 0% to 14% for the phase fractions. However, in the range of 34 at.% to 40 at.% titanium and 30 at.% boron, the deviation between experimental and calculated results was significantly higher, ranging from approximately 20% to 60%. The experimentally determined phase fractions indicate an inaccuracy in the calculated phase transition of the β-(V,Ti)bcc + TiB and the β-(V,Ti)bcc + TiB + V3B2 regions. The calculated phase transitions between the three-phase β-(V,Ti)bcc + TiB + V3B2 and the V3B2 + VB region, as well as the β-(V,Ti)bcc + V3B2 region, show good agreement with the experimental results.
The developed V-Si-B-Ti-Cr database enables the calculation of phase diagrams, compositions, and fractions for all binary and ternary subsystems (excluding the V-B-Cr and B-Ti-Cr systems) of these five elements. Further integration of the datasets for the missing ternary systems would allow for the comprehensive calculation and investigation of the quaternary and quinary systems.