Jyh-Wei Lee^1,2,3,4, Bih-Show Lou^5,6
1Ming Chi University of Technology, New Taipei, Taiwan
²Chang Gung University, Taoyuan, Taiwan
³National Tsing Hua University, Hsinchu, Taiwan
⁴National Taiwan University of Science and Technology, Taipei, Taiwan
⁵Chang Gung University, Taoyuan, Taiwan
⁶New Taipei Municipal TuCheng Hospital, Chang Gung Memorial, Taiwan
The pioneering work on bulk high entropy alloys (HEAs) by Prof. Yeh and coworkers in 2004 has opened a new field of material research due to their unique properties, such as high strength, good ductility, excellent wear resistance, good thermal stability, decent corrosion resistance, and anti-radiation ability of HEAs. Meanwhile, the HEA thin films deposited by the magnetron sputtering technique have been widely studied because of their better corrosion resistance, oxidation resistance, mechanical properties, and wear resistance than the traditional alloy substrates. In this study, the TiZrNbTaFeN HEA nitride, AlCrNbSiTiC HEA carbide, and VNbMoTaWO HEA oxide thin films were fabricated by reactive high power impulse magnetron sputtering (HiPIMS) technique, respectively. The relationships between the nitrogen, acetylene, and oxygen gas flow ratios, respectively, and the chemical compositions of TiZrNbTaFeN nitride, AlCrNbSiTiC carbide, and VNbMoTaWO oxide thin films were studied to understand the multicomponent target poisoning effect. Effects of acetylene and oxygen gas flow ratios on the intensities of optical emission spectrometry signals of high entropy alloy elements (AlCrNbSiTi and VNbMoTaW), carbon, and oxygen species were explored. Meanwhile, the influence of nitrogen, acetylene, and oxygen gas flow ratios on the phase structures, microstructures, and mechanical and electrochemical properties of TiZrNbTaFeN nitride, AlCrNbSiTiC carbide, and VNbMoTaWO oxide thin films were further explored. The phase structures of TiZrNbTaFeN films changed from amorphous to FCC when the nitrogen gas flow ratio and the nitrogen content were higher than 10% and 32 at.%, respectively. The hardness of TiZrNbTaFeN thin films was enhanced from 9.8 GPa to 36.2 GPa by adding 32 at.% N due to the formation of metal-nitride phases and solid solution strengthening effect by various elements. The oxygen concentrations of VNbMoTaWO films increased from 73.6 to 77.5 at.% as the oxygen gas flow ratio increased from 33% to 50%. The electrochemical activity of the VNbMoTaWO films increased with increasing oxygen contents. The vanadium redox flow battery (VRFB) equipped with the VNbMoTaWO modified graphite electrode exhibited a superior energy efficiency of 80.50 % at a current density of 100 mA cm^-2, outperforming the VRFB with the unmodified graphite electrode by 9.49 %. For the AlCrNbSiTiC carbide films, the hardness increased from 16.5 to 18.2 GPa and then decreased to 11.6 GPa as the acetylene gas flow rate increased, and carbon content increased from 42.6 to 55.7 and then 78.4 at.%. The corrosion resistance of AlCrNbSiTiC film against the 0.5 M sulfuric acid increased with increasing carbon content. We can conclude that by properly controlling chemical compositions and reactive gas flow ratios, we can produce functional high entropy alloy thin films with good performance and specific properties, which can be further applied in various environments.