Oxidation Behavior of AlTiN/TiN Nanolayer Hard Coating at High Temperatures

Hard machining and high speed cutting are challenging machining processes demanded for high productivity for several decades. Hard coatings are mostly used for protection of the tool materials from severe tribological conditions in which excessive cutting temperatures and forces take place during these processes. Oxidation resistance is an important property of the hard coatings in hard machining operations due to high temperatures up to 1000C at the cutting edge. Improvement of oxidation resistance provides longer tool life at dry cutting conditions. TiAlN-based coatings are known to have high oxidation resistance. In this paper, nanolayer AlTiN/TiN coating was deposited on cemented carbide substrates by industrial magnetron sputtering system. The need to understand the effect of nanolayered structure on the oxidation behavior of protective coatings in machining industry in terms of high temperature oxidation tests is the motivation of this investigation. The deposited coating was annealed at 1000C with different durations. Before and after the oxidation tests, the composition, structure and phases of the coating were determined by scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively. It was found that nanolayered structure improves oxidation resistance, and thereby, it provides longer tool life.