Dry cutting performance of partially filtered arc deposited titanium aluminium nitride coatings with various metal nitride base coatings

PVD titanium aluminium nitride coatings are known to improve the performance of cutting tools in aggressive machining applications, such as high-speed dry machining. This is generally acknowledged to be due to the fact that these coatings are able to maintain high hardness and resistance to oxidation at the elevated temperatures typically experienced in such metal cutting applications. In this investigation, the performance of single layer coatings of TiN and CrN, and double layer coatings of TiN/TiAlN and CrN/TiAlN were assessed on Co-HSS drills used to machine grey cast iron. It was found that the CrN coatings performed as well as the TiN coatings when drilling grey cast iron. In addition, the double layer coatings outperformed the single layer coatings with the CrN/TiAlN coatings having a 20% improvement in tool life compared with the TiN/TiAlN-coated drills. This result is particularly interesting since the Daimler–Benz indentation test suggested that the TiN/TiAlN had much lower adhesion than the CrN/TiAlN. These results are discussed in terms of an analysis of the physical and mechanical properties of the coatings but it highlights the need for meaningful measurement of critical coating properties which might relate to their performance in metal cutting.