We demonstrate a systematic study optimizing the properties of CoCrFeNi medium entropy alloy (MEA) thin films by tuning the deposition parameters of the pulsed direct current (DC) magnetron sputtering process. The chemical composition and microstructure of thin films were studied with energy dispersive X-ray spectroscopy (EDS), an X-ray diffractometer (XRD) and a transmission electron microscope (TEM). Abundant nanotwins and the dual face-centered cubic-hexagonal close-packed (FCC-HCP) phases were formed in some specimens. The Taguchi experimental method and analysis of variance (ANOVA) were applied to find the optimized parameters. The control factors are five deposition parameters: substrate bias, substrate temperature, working pressure, rotation speed and pulsed frequency. According to the signal-to-noise ratio results, the optimized parameters for low electrical resistivity (98.2 ± 0.8 μΩ·cm), low surface roughness (0.5 ± 0.1 nm) and high hardness (9.3 ± 0.2 GPa) were achieved and verified with confirmed experiments.
Keywords: CoCrFeNi thin films; Taguchi method; magnetron sputtering; medium entropy alloys; nanotwinned structure.