Impact of Al and Cr alloying in TiN-based PVD coatings on cutting performance during machining of hard to cut materials

The microstructure and electronic structure of nanodispersed (Al₆₇Ti₃₃N) and (Ti₁₀Al₇₀Cr₂₀N) PVD coatings were investigated by high-resolution transmission electron microscopy (HRTEM) and electron spectroscopy techniques: X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). The grain size measured by HRTEM was 5-20 nm for Al₆₇Ti₃₃N and TiAlCrN type coatings, correspondingly. The spinodal decomposition of Al supersaturated nitrides under its deposition was found. Chromium increases the metastable solubility of h-AlN in c-Ti_{1 - x}Al_xN. The lifetime of the cutting tools with Al-rich coatings has been evaluated under ball nose end milling of hardened tool steel H13 (HRC 50-52) and aerospace materials. TiAlCrN coatings are preferable for steel machining, and AlTiN coatings are better for aerospace material processing. It was found that AlTiN coating has lower hardness but higher plasticity and improved impact fatigue fracture resistance. The TiAlCrN coating has much better hot hardness and oxidation stability at high temperatures, but it is stiffer than AlTiN.