Development and oxidation behaviour of refractory containing bcc high entropy alloys for high-temperature application

Abstract

This thesis focuses on the design,development and oxidation behaviour of refractory materials containing single BCC phasehigh entropy alloys (HEAs) for high-temperature applications. HEAs, characterized by their unique composition and microstructure, have garnered a recent surge in popularity due to exceptional mechanical and thermal properties. The study aims to understand the microstructure evolution and oxidation behaviour study of Cr-Mn-V-W and Cr- Mn-Ta-V-Wrefractory containing high entropy alloys (HEAs). These alloys were designed by following thermodynamic simulation which was used to understand the evolution of phases using the ThermoCalc software followed by CALPHAD approach.HEAs were developed by two routes (a) mechanical alloying route with the help of ball milling consolidated by SPS(Spark Plasma Sintering) and (b) Vacuum Arc melted route with the help of vacuum arc melting (VAM) unit. The ball-milled powders were taken out for analysis after ball milling for 30min, 5hr, 10hr, 15hr, 20hr, 25hr, 30hr, 35hr, and 40hr, respectively, at a speed of 200 rpm. Microstructures of ball-milled samples were observed by Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS) for chemical composition analysis and XRD was done to confirm the BCC phase. The thermal stability of the SPSed HEAs with respect to temperature has been investigated using two techniques: a Differential Thermal Analyzer (DTA) and a Thermal Gravimetric Analyzer (TGA). The DTA analysis was performed at a temperature of 1400°C, while the TGA analysis was conducted at 900°C (both isothermal and non-isothermal).