Abstract
• AlCrN/Cu coatings were deposited combining cathodic arc evaporation and magnetron sputtering. • Epitaxial growth of Cu sublayers on AlCrN achieves a hardness greater than 30 GPa. • Excessive Cu-incorporation causes the disintegration of the multilayered structure. • Temperate CuO oxide with fine grain size contributes to decreased friction coefficients. • Severe oxidation related to Cu-content leads to inferior tribological properties. Achieving high hardness and low friction at elevated temperatures for nitride-based hard coatings has substantial scientific interest and application significance. In this study, AlCrN/Cu coatings were deposited by a hybrid PVD technique combining arc evaporation from an Al 60 Cr 40 target and magnetron sputtering from a Cu target in a mixed Ar and N 2 atmosphere. The microstructure, oxidation behavior, and tribological properties of the coatings were investigated. AlCrN/Cu coatings show a dual-phase structure of (Al, Cr)N solid solution and Cu metallic phase. Excessive sputtering power of the Cu target induces the disintegration of interlayer interfaces of the nano-multilayered geometry, accompanied by a decline in hardness from above 30 GPa to 22.7 GPa. Moreover, the formation of fine CuO grains on the coating surface is conducive to reducing the friction coefficient of AlCrN/Cu when exposed to air at high temperatures. The AlCrN/Cu coating with a sputtering power of 0.5 kW obtains a friction coefficient of 0.39 ± 0.05 after pre-oxidation at 800 °C, distinctly lower than that of AlCrN, which exhibits a friction coefficient of ∼0.65. The further transformation of CuO to cubic Cu(Al, Cr) 2 O 4 , which stems from the solid-state reaction of CuO, Al 2 O 3 , and Cr 2 O 3 , would cause a rise in friction coefficient and wear loss. The mechanism of oxidation and tribological behavior of the AlCrN/Cu coatings related to the temperature and Cu content was discussed.
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