Mechanical, tribological and anti-corrosion properties of AlCrNbSiTi high entropy coatings with various nitrogen fluxes and application to nickel-based alloy milling

(AlCrNbSiTi)N high entropy alloy coatings were prepared by reactive radio-frequency magnetron sputtering with nitrogen fluxes in the range of 0–20 sccm. The effects of the nitrogen flux on the microstructure, mechanical properties, phase composition, chemical bonds, tribological properties, corrosion resistance, and machining performance of the coatings were systematically examined and compared. All of the coatings exhibited an amorphous structure due to the high mixing entropy effect and large atomic-size difference of the coating elements. The coating hardness increased with an increasing nitrogen flux and reached a value of 43.7 GPa at a flux of 15 sccm. However, a significant reduction in the adhesion strength occurred at a nitrogen flux of 20 sccm as the result of a high residual compressive stress within the coating. The coating deposited with a nitrogen flux of 15 sccm showed the lowest wear rate (0.4 × 10⁻⁶ mm³/N·m) and corrosion current density (0.27 × 10⁻⁷A/cm²) of the tested coatings. The superior tribological performance of the coating was attributed to its high hardness-to-elastic modulus ratio, high hardness cubed-to-elastic modulus squared ratio, and low friction coefficient. Moreover, the improved anti-corrosion performance was the result of a large number of strong chemical bonds within the coating and the high adhesion strength. Finally, the milling test results showed that the addition of nitrogen with a flux of 15 sccm during the deposition process provided an effective reduction in the tool wear when machining Inconel 718 nickel-based alloy.