Thermodynamic modeling and critical experiments in the Al-Nb-V system

Abstract

High entropy alloys are multicomponent alloys that, unlike classic alloys such as nickel steels and superalloys, do not have a principal element, each of its components composing the alloys in contents between 5 and 35 at.%. One of the possible branches of application for these alloys is the aeronautical industry, particularly those made of high melting point and low density metals, where they may complement the nickel superalloys in applications at high temperatures. The Al-Nb-Ti-V-Zr system is one of the systems of interest in the Phase Diagram and Computational Thermodynamics Group of Demar-EEL-USP. Among the 10 ternary subsystems, the Al-Nb-V ternary is one of the least studied, with only one complete isothermal section at 1000 °C reported in the literature. The objective of this project is to develop a thermodynamical modeling of the Al-Nb-V ternary system and to perform critical experiments in order to better understand the phase relations in the system. Based on the modeling of the Al-Nb, Al-V and Nb-V binaries reported in the literature, an extrapolation will be made for the ternary that should point out the alloys to be made for the study of its liquidus projection. Based on the 1000 °C isothermal section reported in the literature, samples will be produced with compositions inside the three-phase equilibrium triangles to confirm available information. Samples for the study of the isothermal section will be treated at 1200 °C in order to achieve thermodynamic equilibrium at reasonable times. The samples will be produced by arc melting pure elements, under argon atmosphere in a water cooled copper crucible. The samples will be treated at 1200 °C, wrapped in niobium sheets and encapsulated in quartz tubes under agon atmosphere. The microstructures of the samples will be characterized by X-ray diffraction and scanning electron microscopy and the compositions of the present phases will be measured by electronic microanalysis (EDS / WDS). The experimental results will serve as input for thermodynamic modeling of the ternary. (AU)