Development and Characterization of Eutectic V-Si-B Alloys with Advanced Specific Mechanical Properties for High Temperature Applications: Role of the New V8SiB4 Phase

• Applicants: Professorin Dr.-Ing. Bronislava Gorr; Dr.-Ing. Georg Hasemann; Professorin Dr. Ruth Schwaiger
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins ; Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410338871

V-Si-B alloys have great potential for high-temperature structural applications. In the first funding period the phase diagram including the liquidus projection and the isothermal section at 1400 °C were developed and investigated for the V-rich V-Si-B system. In these investigations, a new ternary phase, V8SiB4, was discovered, whose crystal structure was determined by combining experimental results and density functional theory calculations. According to the literature and the current status of our own results, the formation temperature of the V8SiB4 phase can be assumed to be in the range between 1400 °C and 1600 °C from the V5SiB2 phase. This appears to be a transformation from the V5SiB2 phase. Furthermore, the mechanical properties of the Vss−V3Si−V5SiB2 and the Vss−V5SiB2 eutectic alloys were investigated in the temperature range from 25 °C to 1000 °C. The primary objective of this follow-up proposal is to investigate the phase stability of the new V8SiB4 phase depending on the temperature and the alloy composition. A monolithic V8SiB4 phase will be produced using powder metallurgy (PM), i.e. mechanical alloying and sintering (FAST). The postulated solid-solid transformation behavior will be investigated via DSC measurements in combination with purposefully selected heat treatment experiments.To determine the solubility range of the V8SiB4 phase, 2-3 variants with slight variations in the stoichiometry of the new phase will be prepared and investigated. In addition, EDX and/or WDX measurements will be performed to narrow down the solubility range. Subsequently, the V-Si-B database (FactSage) created in the previous project period will be expanded to include the latest findings. As a second focus of the proposed project, the mechanical behavior of the V8SiB4 phase will be investigated on the micro- and macroscales. V8SiB4 and V5SiB2 phases will be studied by nanoindentation and electron microscopy to characterize the deformation mechanisms and mechanical properties as a function of crystal orientation. On the macroscale, the compressive yield strength and the creep resistance of polycrystalline V8SiB4 and V5SiB2 phases will be tested at 900 °C and 1000 °C. The determined mechanical parameters of the two intermetallic phases will then be applied in a model to describe the deformation parameters of an alloy from the first funding period.

• DFG Programme: Research Grants
• Co-Investigator: Professorin Dr.-Ing. Manja Krüger