Oxidation post-treatment of hard AlTiN coating for machining of hardened steels

In this study, cemented carbide ball nose end mills with nano-crystalline Al_0.67Ti_0.33N hard PVD coatings deposited by cathodic arc evaporation were annealed at 700 °C during 2 h in a controlled atmosphere environment (argon + oxygen mixture) and in vacuum. The changes of structure and properties of the treated coating surfaces have been analyzed using both cross-sectional scanning electron microscopy (SEM) and x-ray absorption spectroscopy (XAS) of the N-K and O-K edges. Cutting tools have been run through ball nose end milling of hardened H13 steel (HRC 50) where temperature or stress dominating phenomena control tool life. The data obtained indicate that an AlTiN coated cutting tool can be modified upon annealing at low temperature conditions and should be considered as a composite surface engineered material. It is shown that increased tool life could be achieved if annealing of AlTiN is performed in an oxygen-containing atmosphere. A variety of different characteristics should be optimized to achieve better wear resistance of the cutting tools with annealed Al_0.67Ti_0.33N coating under high temperature and stress cutting conditions.