Structure and properties of the TiN and Ti(C,N) coatings deposited in the PVD process on high-speed steels

Abstract

This paper presents investigation results of the influence of substrate type made from the W–Mo–V+Si high-speed steels with addition of Nb or Ti, or else from the Mo–V–Co+Si steel with the economically selected chemical composition, and from the sintered steels of the ASP 23 and ASP 30 types, on structure and properties of the hard, wear resistant, TiN, titanium nitride, and Ti(C,N), titanium carbonitride coatings, put down in the PVD process. It was demonstrated that the high-speed steels containing 9–11% of tungsten, 2% of molybdenum, 0.7% of silicon, in which vanadium was partially substituted by 0.5% of niobium or 0.3% of titanium, covered with the investigated coatings in the PVD process, demonstrate properties comparable to those obtained on the sintered high-speed steels of the ASP 23 and ASP 30 types. It was found out that the investigated TiN and Ti(C,N) coatings display the columnar structure with the clear axial texture {111}, with the solidified titanium drops deposited directly onto the substrate or coating layers developed earlier, and also with pits developed by falling out by some of these drops. The TiN and Ti(C,N) coatings display a good adhesion to the substrates from the investigated high-speed steels, and it is not only the adhesion deciding this but also the diffusion or ion implantation connected mix of elements in the transition zone between the coating and its substrate. The Ti(C,N) coatings display double erosion resistance compared to the TiN ones. The erosion resistance grows along with increasing of the coating hardness, whereas neither the critical load value in the adhesion test, nor the chemical composition do not have any significant effect. This makes it possible to exploit in practice high-speed steels with the relatively low concentration of the alloying elements instead of the high-alloy cobalt steels, provided the substrate’s heat treatment is made so that it ensures its maximum secondary hardness. Moreover, a new methodology was developed for evaluation of the erosion resistance of materials coated in the PVD process, employing the computer image analysis on the scanning electron microscope.