Article

Metallurgical and Materials Transactions A

, Volume 38, Issue 10, pp 2464-2478

First online:

Oxidation Behavior and Mechanisms of TiAlN/VN Coatings

  • Z. ZhouAffiliated withDepartment of Engineering Materials, University of Sheffield
  • , W.M. RainforthAffiliated withDepartment of Engineering Materials, University of Sheffield Email author 
  • , C. RodenburgAffiliated withDepartment of Engineering Materials, University of Sheffield
  • , N.C. HyattAffiliated withDepartment of Engineering Materials, University of Sheffield
  • , D.B. LewisAffiliated withMaterials Engineering Research Institute, Sheffield Hallam University
  • , P.E. HovsepianAffiliated withMaterials Engineering Research Institute, Sheffield Hallam University

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Abstract

Hard wear-resistant coatings require excellent oxidation resistance for high-speed machining operations. Moreover, the oxide formed is integral to the frictional behavior and therefore the success of the coating. The oxidation behavior of TiAlN/VN nanoscale multilayer coatings was investigated using high-resolution techniques and was compared with TiN and TiAlN coatings. Static oxidation of TiAlN/VN films was studied in the range 550 °C to 700 °C, and characterized by high-temperature in-situ X-ray diffraction (XRD) and scanning transmission electron microscopy/energy-dispersive X-ray/electron energy loss spectroscopy (STEM/EDX/EELS) of selected surface cross sections. The oxidation resistance of TiAlN/VN was found to be controlled by the VN layers, and consequently, oxidation was initiated at a lower temperature than TiN and TiAlN coatings. The onset of oxidation of the TiAlN/VN coating was found to be ≥550 °C with the VN being the first component to oxidize. At temperatures >600 °C, a duplex oxide structure was formed; the inner layer comprised a porous region of Ti-rich and V-rich nanocrystallites, while several phases were observed in the outer region, including V2O5, TiO2, and AlVO4. V2O5 was the dominant oxide at the outer layer at ≥638 °C. The outward diffusion of V depended on the species present; in the inner layer, V was present as V3+, V4+, whereas a significant V5+ was dominant in the outer layer of oxide at ≥638 °C. An Au marker study suggested roughly equal diffusivity of cations outward, and oxygen inward diffusion occurred during oxidation.