High entropy alloy thin films of AlCoCrCu0.5FeNi with controlled microstructure

Abstract High entropy alloys in the form of thin films have been of growing interest in the past few years due to their unique properties such as high corrosion resistance, superior hardness, and high electrical resistivity. We used RF magnetron sputtering to fabricate high entropy alloy thin films of AlCoCrCu0.5FeNi. To tune the microstructure and mechanical properties of the films, three different working pressures of 5, 10, and 15 mTorr were utilized. The films grown at 10 mTorr had the largest grain size with highest surface roughness measured by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. Energy dispersive spectroscopy (EDS) results show that films grown at lower pressure (5 mTorr) are X-ray amorphous and have significantly higher concentration of aluminium (over 35%) due to the reduced scattering of Al atoms on route to the substrate. The films deposited at 10 mTorr are composed of a mixture of FCC and BCC crystal structures as determined using X-ray diffraction (XRD); have protective surface oxide layers of Al2O3 and Cr2O3, as observed by X-ray photoelectron spectroscopy (XPS); and have high electrical resistivity (over 4500 μΩ-cm) and high hardness (over 13 GPa). This work shows that the deposition pressure is a critical growth parameter that can be used to tune the microstructure and the properties of sputter deposited HEA thin films with potential applications as protective and hard coatings for aerospace and energy applications.