Mechanical properties and impact resistance of multilayered TiAlN/ZrN coatings

Transition metal nitrides, such as ZrN and TiAlN, have been used as protective hard coatings due to their excellent tribological properties. In this study, ZrN, TiAlN and multilayered TiAlN/ZrN coatings were synthesized by cathodicarc evaporation with plasma enhanced duct equipment. Zirconium and TiAl (50 at% of Al) alloy cathodes were used for the deposition of TiAlN/ZrN coatings. During the coating process of multilayered TiAlN/ZrN, ZrN was deposited as an interlayer. With different cathode current ratios (I-[TiAl]/I-[Zr]) of 0.75, 1.0, and 133, the deposited multilayered TiAlN/ZrN coatings possessed different chemical contents and modulation periods. The nanolayer thickness and alloy content of the deposited coating were correlated with the evaporation rate of cathode materials. Modulation period and layer thickness ratio of TiAlN/ZrN increased with increasing I-[TiAl]/I-[Zr] cathode current ratio. The multilayered TiAlN/ZrN coatings possessed higher hardness of 33-38 GPa than that of the monolayered ZrN(30 GPa) and TiAlN(31 GPa) coatings. To study the correlation between impact fracture resistance and hardness/modulus ratio, an impact test was conducted using a tungsten carbide ball as an impact indenter. The multilayered TiAlN/ZrN coating with the lowest modulation period (25 nm) and the highest layer thickness ratio of TiAlN/ZrN (0.92) exhibited the best impact resistance (higher than 1x10(5) impacts) and the highest H-3/E-*2 ratio value of 0.443 GPa, indicating the best resistance to plastic deformation, among the studied TiAlN, ZrN and multilayered TiAlN/ZrN coatings. (C) 2012 Elsevier B.V. All rights reserved.