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 performanc e of cutting tools in aggressive machining applications, such as high-speed dry machining. This is generally acknowledged to be due to the fact that t hese coatings are able to maintain high hardness and resistance to oxidatio n at the elevated temperatures typically experienced in such metal cutting applications. In this investigation, the performance of single layer coatin gs of TiN and CrN, and double layer coatings of TiN/TiAlN and CrN/TiAlN wer e assessed on Co-HSS drills used to machine grey cast iron. It was found th at the CrN coatings performed as well as the TiN coatings when drilling gre y cast iron. In addition, the double layer coatings outperformed the single layer coatings with the CrN/TiAlN coatings having a 20% improvement in too l life compared with the TiN/TiAlN-coated drills. This result is particular ly interesting since the Daimler-Benz indentation test suggested that the T iN/TiAlN had much lower adhesion than the CrN/TiAlN. These results are disc ussed in terms of an analysis of the physical and mechanical properties of the coatings but it highlights the need for meaningful measurement of criti cal coating properties which might relate to their performance in metal cut ting. (C) 2001 Elsevier Science B.V. All rights reserved.