Deposition of arc TiAlN coatings with pulsed bias

Abstract

It is a well-known fact that the aluminium content of TiAlN coatings deposited with the arc physical vapour deposition (PVD) process depends mainly on substrate potential and source-to-substrate distance. To achieve good results in cutting operations with TiAlN-coated tools with a low aluminium content in the film, it is necessary to deposit TiAlN with a relatively high bias voltage which raises the substrate temperature to a level which can cause some damage to the structure of even high speed steel substrates. For high performance cutting operations with TiAlN thin films a high and homogeneous aluminium content in the films, especially on cutting edges, is necessary. Higher aluminium content in arc PVD thin films is achieved with lower bias voltage during deposition which in turn lowers the deposition temperature and consequently enables heat-sensitive substrates to be coated; however, for good adhesion of the deposited films a high bias voltage is required. The application of a pulse bias generator instead of a d.c. bias offers the possibility to decrease the deposition temperature and to obtain more aluminium in the coating. In this paper we compare coating properties of TiAlN deposited with d.c. and pulsed bias source. With pulsed bias it is possible to achieve higher aluminium content in the coating, especially on cutting edges. Analysis of increase in aluminium on cutting edges was carried out by energy-dispersive X-ray analysis.