Mechanical properties and thermal stabilities of multilayered AlCrBN/AlTiSiN hard coatings

Abstract

AlCrN and AlTiN coatings are widely used in cutting tools and forming dies due to their favorable mechanical properties, tribological characteristics, and oxidation resistance achieved by incorporating Al into CrN and TiN. While AlCrN coatings demonstrate good oxidation resistance , AlTiN coatings exhibit high hardness at elevated temperatures. The addition of silicon (Si) into AlTiSiN and boron (B) into AlCrBN coatings is known to improve their mechanical properties. Furthermore, to enhance these coatings even more, multilayer designs have been developed. Leveraging the additions of Si and B, AlCrBN/AlTiSiN multilayer coatings , along with AlCrN and AlTiN monolithic coatings without Si and B additives, were fabricated using a cathodic arc ion plating method. Their thermal stability at 900 °C and 1000 °C in vacuum was investigated to meet the demands of high-temperature applications. In this study, composition-gradient and periodic layering structures were employed for depositing the multilayered AlCrBN/AlTiSiN coatings. The results revealed that the vacuum-annealed AlCrBN/AlTiSiN multilayer structure inhibited the formation of hexagonal Cr 2 N (h-Cr 2 N), which could compromise mechanical properties, while also maintaining the coating hardness due to phase decomposition. In contrast, the hardness of AlCrN coatings decreased consistently at 900 °C, showing the lowest thermal stability of all coatings in this study. The AlCrBN/AlTiSiN coating maintained its hardness at 900 °C and 1000 °C for 1 h and even experienced a slight increase to 28.9 ± 0.6 at 900 °C after 4 h. It demonstrated that it possessed the ability to sustain or even improve its mechanical properties at high temperatures. In addition to maintaining thermal stability, the enhanced oxidation resistance at elevated temperatures makes multilayered AlCrBN/AlTiSiN coatings suitable for use in high-temperature environments.

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