Microstructural characterization of refractory high entropy alloys

• Grant number: 18/13776-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2018
• End date: September 30, 2019
• Field of knowledge: Engineering - Materials and Metallurgical Engineering
• Principal Investigator: Marcelo Falcão de Oliveira
• Grantee: João Henrique Mazo
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

High entropy alloys has been a recent target of interest to the industrial and technological area, mostly for being materials that have superior properties than traditional alloys and that still have a vast area yet to be explored inside its possibilities. Some of its properties noticed until now are: superconductivity, elevated tenacity and high corrosion resistance, properties that can be combined with refractory properties in order that alloys with the desired characteristics can be formed. Recent researches in the area have shown that HEAs (High Entropy Alloys) have a high tendency to form solid solutions instead of intermetallic, which is due to the high configurational entropy of the alloy, since the alloys have at least five elements in a minimum proportion of 5%. Because of the prioritary forming of solid solutions, the great majority of the structures formed in these alloys are well known, such as body centered cubic (BCC) and face centered cubic(FCC).However, some difficulties have been noticed referent to the HEAs, those difficulties include the lack of methods to manipulate the alloy composition according to the desired structure and properties of the material, since that its phase diagram is hyperdimensional and its not easy to predict what happens in its center. Besides that, sample production also have difficulties that need to be overcome trough the creation of efficient methods so that the alloy composition its as precise as possible. The objective of this project is to characterize refractory high entropy phases with different compositions, having a fixed Al and Cr composition (since Al have a low density and the both metals have a high solubility to one another in high temperatures and have a low solubility with the other alloy elements) together with refractory metals like Nb, Zr, Mo, Ta and W. After the production by arc melting in inert atmosphere, the samples will be sanded, polished and attacked in order that they are properly prepared to an analysis of the microstructure trough an optic microscope. The investigation of those phases will be complemented trough Energy Dispersion Spectrometry (EDS) in a scanning electron microscope(SEM) to identify the elements that compose the phases of interest.