Fabrication and Microscopic Characterization of AlCoCrCu0.5FeNi High Entropy Alloy Thin Films

Abstract

The high entropy alloy (HEA) was first discovered and reported in 2004. It was also called multi-principal element alloys (MPEAs). Generally, it is consisted of at least five elements in equimolar or near equimolar ratios, and the concentration of each element is varied in between 5% and 35%. HEAs have many useful properties like thermal stability, excellent mechanical properties and high corrosion resistance which can all be applied in practice for various applications, such as high temperature, heat resistant coatings and diffusion barriers. They can also be used as the raw materials for soft magnetic films. This thesis is focused on fabrication, microscopic structural characterization and property measurements of AlCoCrCu0.5FeNi high entropy alloy thin film fabricated at temperatures, from room temperature up to 350 oC by using Radio Frequency (RF) magnetron sputtering. The RF magnetron sputtering experiments were conducted in the School of Physics at the University of Sydney. Surface energy tests, Scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Energy dispersive x-ray spectroscopy (EDS) were used to study the surface contact angles, the surface morphologies, the crystal structures, and the atomic concentrations of the high entropy alloy thin films. In this study, FCC, BCC and the mixtures of both were found by using XPS and XRD. Thin films fabricated under higher temperatures was found to have the surface morphology with high roughness and large grain size by using SEM and EDS. With higher residual gases, the films presented with high density, hardness, and with higher Aluminum atomic concentration, the crystalline structures trended from FCC (111) to BCC (110). In conclusion, the mobility/energy of HEA atoms or ions, the Aluminum atomic concentration and the residual gases concentration, those three factors played important roles in fabricating different films. Thus, temperature was proved to be a key aspect in exploring new fabricating methods.