Mechanical and tribological characterization of tools coatings for dry tapping

Abstract: In the past years several efforts have been done to develop techniques for dry machining, at present limited to soft materials, especially in difficult machining operations like tapping. Hard materials like High Speed Steels requires the development of suitable tools surfaces. On the other hand, for reducing time and costs, a reliable forecast over the machining behaviour of the coatings would be desirable. For these purposes, a new developed nanocomposite coating, consisting of nanocrystalline TiN and amorphous Si3N4, was deposited on high speed steel (HSS) taps via Plasma Activated CVD and its performance tested in tapping of HSS workpieces under dry condition. Such behaviour was compared to that of TiN and TiCN coatings, traditionally employed in this field. Mechanical and tribological properties of the coatings were studied and related to machining behaviour. The nanocomposite coated tool showed higher tool life in tapping; this behaviour was explained in terms of good wear resistance and good adhesion between coating and substrate. Analysis of the results indicated characterization tests able to give a reliable forecast over the machining performance of the coatings