Effect of Nitrogen Pressure on the Fabrication of AlCrFeCoNiCu0.5 High Entropy Nitride Thin Films via Cathodic Arc Deposition

Abstract

High entropy alloys (HEAs), consisting of five or more than five elements in equal or nearly equal proportions, usually exhibit superior mechanical properties, outstanding corrosion & oxidation resistance, and exceptionally high thermal stability compared to traditional alloys. HEA thin films possess further improved mechanical properties due to their nanocrystalline microstructure. Compared to HEA thin films, high entropy nitrides (HENs) have even higher mechanical strength and chemical inertness. AlCrFeCoNiCu0.5 HEN thin film is reported to be an extraordinarily hard material that possesses high levels of surface protective nitrides layer, while limited work of AlCrFeCoNiCu0.5 HEN thin film deposited by cathodic arc has been done. In this work, AlCrFeCoNiCu0.5 HEN thin films were deposited on (100) Si wafer using a filtered cathodic arc. The nitrogen concentration for each thin film was regulated by changing pressure during depositions, tuning the distortion energy and mechanical properties. STEM-EDS revealed increased aluminium concentration as pressure increased. X-ray photoelectron spectra revealed that AlN was the preferred nitride formed. Interstitial solid solution of nitrogen enhanced the lattice distortion in the HEN films, while stronger covalent bonds contracted the crystal lattice according to XRD and HRTEM images. Amorphization was observed in the thin film with increased pressure. The mechanical properties of the cathodic arc deposited AlCrFeCoNiCu0.5 HEN thin films were found to improve when pressure increased with the highest hardness of 12.4  0.6 GPa and elastic modulus of 347.3  17.7 GPa found at the highest pressure of 0.05 Pa. These mechanical properties were significantly enhanced compared to those of similar films fabricated by RF magnetron sputtering.